Aircraft System
Aircraft System
Aircraft System
PASCALL’S LAW
“If a force is applied to a liquid in a confined space, then this force will be felt equally
in all directions”.
BRAMAH’S PRESS
a) The smaller the area under load, the greater the pressure generated.
b) The larger the area under pressure, the greater will be the load available.
The ideal properties of a hydraulic fluid are:
a) 2
e relatively incompressible, i.e. up to 2.7.6 MN/m (276 Bar), so ensuring
instantaneous operation.
b) Have good lubricating properties for metal and rubber
c) Have good viscosity with a high boiling point (helps prevent vapour locking and
cavitation) and low freezing point e.g. temperature range +80°C to -70°C.
d) Have a flash point above 100°C.
e) Be non-flammable.
f) Be chemically inert.
g) Be resistant to evaporation.
h) Have freedom from sludging and foaming.
i) Have good storage properties.
BASIC SYSTEM
There are six main components common to all hydraulic systems:
A reservoir of oil, which delivers oil to the pump and receives oil from the
actuators.
A pump, either hand, engine or electrically driven.
A selector or control valve, enabling the operator to select the direction of the flow
of Fluid to the required service and providing a return path for the oil to the
reservoir.
A jack, or set of jacks or actuators, to actuate the component.
A filter, to keep the fluid clean.
A relief valve, as a safety device to relieve excess pressure.
OPEN-CENTRE SYSTEM
The main advantage of this system is that it is simple, the main disadvantage is
that only one service can be operated at a time.
The relief valve will relieve excess pressure if the selected does not return to its
neutral position.
This type of system is popular in many light aircraft which do not require a constant
pressure to be maintained all the time as only items like landing gear and flaps
will be powered for short periods of time each fligh
With this type of system, operating pressure is maintained in that part of the
system which leads to the selector valves, and some method is used to
prevent over-loading the pump. In systems which employ a fixed volume
pump (constant delivery) an automatic cut-out valve is fitted, to divert pump
output to the reservoir when pressure has built up to normal operating
pressure.
● To allow ground servicing to take place without the need for engine running to
operate cargo doors etc.
● So that lines and joints can be pressure tasted.
● For emergency lowering of ldg. gear in some aircraft
1. Liquid boils when its vapour Px is more than Ambiant Px.
2. At high altitudes fluids boils early (evaporate) due to lox Px.
3. This is the reason why all the tanks (Fuel tank, water tank, hydraulic tank should
be pressurized to prevent evaporate at high altitude and also to prevent pump
cavitation by providing fluid at a post Px to the pump inlet.
4. The primary purpose of reservoir is no store fluids to compensate for small balls.
RESERVOIRS
A reservoir provides both storage space for the system fluid, and sufficient air space
to allow for variations of fluid in the system which may be caused by:
● Jack (actuator) ram displacement, since the capacity of the jack is less when
contracted than extended.
● Thermal expansion, since the volume of oil increases with temperature.
● It provides a head of fluid for the pump.
● It compensates for small leaks.
● Most reservoirs are pressurized, to provide a positive fluid pressure at the pump
inlet, and to prevent air bubbles from forming in the fluid at high altitude.
● Air pressure is normally supplied from the compressor section of the engine, of
the cabin pressurization system or by compressed cylinders of N2, Nitrogen.
PUMPS
Draw oil from the reservoir and deliver a supply of fluid to the system. Pumps may
be:
a) Hand Operated
b) Engine Driven
c) Electric Motor Driven
d) Pneumatically (Air Turbine Motor) (ATM)
e) Ram Air Turbine (RAT)
f) Hydraulically (Hyd, Motor Driving A Hyd. Pump) known as a power transfer
unit or PTD. In most cases the ATM, RAT or PTU is used to provide an
alternate supply as part of the redundancy provision for the safe operation of
the aircraft.
Engine driven pumps (EDP) or electrically driven pumps may be classified as
follows:
1. Constant Delivery (Fixed Volume) Type Pump –
i) Output is X RPM
ii) Must have fluid at positive Px at pump inlet, to prevent
cavitation
iii) Constant volume pump has to have on Acav.
This pump supplies fluid at a constant rate and therefore needs an automatic cut-out
or relief valve to return the fluid t the reservoir when the jacks have reached the end
of their travel, and when the system is not operating, it requires an idling circuit.
Axial pump/constant Px pump/variable volume pump upon engine shut-down swash
plates stops at Max. Stroke angle for immediate Px build-up on next start.
HYDRAULIC ACCUMULATORS
An accumulator is fitted:
a) To store hydraulic fluid under pressure.
b) To dampen pressure fluctuations.
c) To allow for thermal expansion
d) To provide an emergency supply of fluid to the system in the event of pump
failure.
e) To prolong the period between cut-out and cut-in time of the ACOV and so
reduce the wear on the pump
f) Provides the initial fluid when a selection is made and the pump is cut-out.
The gas side of the accumulator is charged to predetermined pressure with air
and Nitrogen
Incorrect pre-charge pressure of the main accumulator can cause the ACOV to
cut in and out too frequently.
This may cause rapid fluctuations of system pressure which can be felt and heard
as ‘hammering’ in the system. (Poppat valve is making noise)
The initial gas charge of the accumulator is greater than the pressure required to
operate any service, and the fluid volume is usually sufficiently large to operate
any service once. Gas is compressed until it equalizes the normal system
pressure.
HYDRAULIC LOCK
When fluid is trapped between the piston of the jack and a non-return valve, a
“hydraulic lock” is said to be formed. Because the fluid is incompressible and is
unable to flow through the system, THE PISTON CANNOT MOVE even if a load
is applied to it and is therefore locked in its position.
PRESSURE CONTROL
BALL-TYPE RELIEF VALVE
Hydraulic fuses, which sense increased flow rate are fitted upstream of components
that could be a potential source of an external leak. Under normal conditions, the
piston is held against its stops by combination of fluid pressure and spring force.
If a leak occurs downstream of the fuse, a pressure differential occurs the piston,
resulting in the piston moving across and blocking the flow.
While the service downstream of the fuse is lost, the other services supplied by the
system remain serviceable.
a) SAFETY VALVE (Out flow relief value) A simple mechanical outwards pressure
relief valve fitted to relieve positive pressure in the cabin when the maximum
pressure differential allowed for the aircraft type is exceeded i.e. prevent the
structural max. diff. being exceeded. This valve will open if the pressure rises to
max. Diff. plus 0.25 psi.
b) INWARDS RELIEF (INWARDS VENT) VALVE. A simple mechanical inwards
relief valve is fitted to prevent excessive negative differential pressure which will
open if the pressure outside the aircraft exceeds that inside the aircraft by 0.5 to
1.0 psi.
c) DUMP VALVE. A manually operated component, the Dump Valve, will enable the
crew to reduce the cabin pressure to zero for emergency depressurization. This
valve may also be used as the air outlet during manual operation of the
pressurization system an aircraft fitted with pneumatic discharge valves.
d) DITCHING VALVE – Addition some pressure controllers are fitted with a ditching
control which will close all the discharge valves to reduce the flow of water into
the cabin in the event of a forced landing on water. It helps A/C float on water
due to air inside it.
RATE OF CHANGE
The term rate of change, or ROC, is given to the value by which the cabin altitude is
allowed to ascent or descent. This is normally given in feet per minute or fpm.
However, ROC can also be used as rate of climb and ROD used for rate of descent.
The aircraft also has a rate of change.
The maximum rate of ascent is 500 fpm and 300 fpm for descent respectively.
These rates have been determined by passenger comfort due to the human ear
physiology.
SYSTEM OPERATION
The schematic arrangement of the pressurization control system of a modern
passenger transport aircraft.
INPUTS
The automatic controllers are duplicated and have inputs from the aircraft static
pressure sensing system the cabin pressure and air/ground logic system.
If pre-pressurisation is part of the schedule then inputs will be required from the
thrust lever positions and the door warning system. The cabin altitude control panel
is generally be fitted to overhead panels on the flight deck.
There are two modes of operation, auto (1 & 2) and manual with the outflow valves
being electrically operated by either of the two AC motors under the control of the
automatic controllers or by the DC motor for emergency or manual operation.
Selection of manual will lock out all normal automatic functions and enable the
outflow valve(s) to be positioned by the manual control switch via the DC motor.
The pilot will set the controller to produce the required flight profile.
Taxi. When the aircraft begins to taxi the pressurization GROUNDFLIGHT switch is
selected to FLIGHT and the aircraft is pre-pressurised to a differential pressure of
0.1 psi. This ensures that the transition to pressurized flight will be gradual and that
there will be no surges of pressure on a rotation and ingress of fumes from engines
etc.
Take off and climb. As the aircraft takes off, the ‘ground / air’ logic system will signal
the controller to switch to proportional control. The controller will sense ambient
and cabin pressure and position the outflow valves to control the rate of change of
cabin altitude in proportion to the rate of climb of the aircraft (between 300 and 500
feet per minute).
Cruise. When cruise altitude is reached the controller will switch to ISOBARIC
CONTROL to maintain a constant differential pressure.
Once established in the cruise small changes in altitude (+/-500 – 1000 feet) will be
accommodated without any change in cabin pressure, however if the cruise altitude
has to be increased significantly, then the flight altitude selection will have to be
reset.
If the maximum differential pressure has been reached the controller will not allow
any further increase in differential pressure and the aircraft will now be in Max. Diff.
Control.
Descent and landing. At commencement of the descent the controller will switch
back to proportional control and will give a cabin rate of descent of 300 feet/minute to
produce a diff. pressure of 0.1 psi on touchdown (airfield altitude – 200 feet).
With the ‘ground/air’ logic system now in ground mode, changing the cabin pressure
controller GROUND/FLIGHT switch to GROUND will drive the outflow valves to fully
open to equalize cabin and ambient pressures. And Max. Differential to ZERO.
To summarise:- If the differential pressure is increasing the discharge valves are
closing, if the differential pressure is decreasing then the discharge valves are
opening and if the differential pressure is constant then, since the mass flow in is
constant, the discharge valve will not move.
↳
Bleed air system with air being ducted from two stages of the compressor, a low
The two sources are combined together at the High Pressure Shut-Off valve
(HPSOV). This valve is pressure sensitive and pneumatically operated and is open
when there is insufficient air pressure from the LP system to maintain the required
flow. As the engine speeds up the LP air pressure will increase until it closes the
high pressure shut-off valve so that, in all normal stages of flight, bleed air will come
from the LP stages.
The high pressure shut-off valves are designed to open relatively slowly on engine
start up or when air conditioning is selected to minimize the possibility of a surge of
air pressure. They are also designed to close very quickly to prevent an ingress of
fumes or fire to the cabin in the event of an engine fire.
The bleed air control valve is the separation point between the engine and the
pneumatic system manifold and allows the bleed air to enter the pneumatic system
and is controlled electrically from the flight deck.
**Non-return valves (NRV) are installed in the LP stage ducts to prevent HP air
entering the LP stages of the engine when the high pressure shut-off valve is open.
So won’t back pressure.
Most multi-engine aircraft also keep the supplying engines or sides separate with
each engine supplying its own user services. These are kept independent by
ISOLATION VALVES which are normally closed but which may be opened if an
engine supply is lost to feed the other side’s services.
The system will also be fitted with safety devices to prevent damage to the supply
ducting due to over pressure or overheat.
a) OVER PRESSURE
This is usually caused by failure of the high pressure shut-off valve and a
pressure relief valve is fitted to the engine bleed air ducting.
If the over pressure persists, a sensor bleeds high pressure shut-off valve opening
pressure and forces the valve to close.
b) OVERHEAT
An electrical temperature switch downstream of the bleed air control valve will close
the valve if the temperature of the air reaches a predetermined level.
Both overheat and over pressure conditions will be indicated to the pilots by warning
lights. If an overheat occurrence took place, the bleed valve switch would be
selected ‘OFF’ and the isolation valve opened to restore the lost system.
BASIC PRINCIPLES OF AIRCRAFT AIR CONDITIONING
As aircraft are going to be operated at different flight levels in different temperature
zones around the world, the aircraft’s air conditioning system must be capable of
taking extremely cold air and warning it, or extremely hot humid air and cooling and
dehumidifying it.
REQUIREMENTS OF AIR CONDITIONING SYSTEM
1. Provision of fresh air – Fresh air must be provided at a rate of 1 lb per seat
per minute in normal circumstances, or at not less than 0.5 lb following a
failure of any part of the duplicated air-conditioning system
2. Temperature Cabin air temperature should be maintained within the range
65°F to 75°F, (18°C to 24°C)
3. Relative humidity – The relative humidity of the cabin air must be maintain at
approximately 30% (at 40,000 ft the relative humidity is only 1 to 2%)
4. Contamination – Carbon monoxide contamination of the cabin air must not
exceed 1 part in 20,000.
5. Ventilation – Adequate ventilation must be provided on the ground and
during unpressurised phases off light.
6. Duplication – The air-conditioning system must be duplicated to the extent
that no single component failure will cause the provision of fresh air to fall to
rate which is lower than 0.5 lb per seat per minute.
Hot bleed air is taken from a gas turbine’s compressor. This heated air, often
referred to as charge air, is then split and a proportion cooled, before it is mixed
together to achieve the required temperature.
Cooling the charge air is a major function of the pack. There are two different
methods in which this can be achieved, the use of air as a cooling medium referred
to as Air Cycle, or the use of a Refrigerant referred to as vapour cycle.
AIR CYCLE MACHINES
The component that cools the charge air is termed a Cold Air Unit or CAU. There
are three different designs. Each comes under the heading of air cycle
machines. The types are :
❖ THE BOOTSTRAP
❖ THE BRAKE TURBINE
❖ THE TURBO FAN
BOOTSTRAP IN CONJUNCTION WITH A MECHANICAL BLOWER
This type of system is used on larger piston-engine aircraft and smaller turboprop
aircraft, where the engines are not designed to supply bleed air for the aircraft’s air
condition system.
The functions and location in the system is what DGCA wants you to know
BLOWER
Ambient air is drawn into a blower. The blower consists of two lobes which are
engine driven, and geared to rotate and mesh. This draw a large volume of air in
and forces it into the supply duct. The restriction of the duct raises both air pressure
and temperature.
BBB
Since the blower is mechanical, it requires lubrication.
Failure of the oil seals can result in blue smoke in the aircraft as the oil vaporizes
in the hot air.
The rotation of the lobes creates a pulsing, changing air pressure (whomp-whomp
effect), which is removed by the silencer unit located downstream.
SPILL VALVE AND FLOW CONTROL VALVE
FUNCTION - The spill valve is designed to allow charge air to bleed overboard
(leave the airplane) in different conditions and is linked to the flow control valve.
LIVE SMOKE
During flight, the flow control valve, also referred to as a mass flow controller,
determines the correct mass of air passing through the system to ventilate the
aircraft. This is done by venting charge air to atmosphere.
MASS FLOW CONTORL
As the aircraft climbs and the ambient density decreases, the flow control
valve progressively closes the spill valve ( so more air can get in).
In the event of an engine fire, to prevent contamination of the cabin air, the spill valve
is fully opened when the pilot operates the engine’s fire handle.
A non-return valve (NRV) is fitted downstream of the spill valve to prevent loss of
cabin air pressure in the event that the spill valve is opened or failure of the blower.
DUCT RELIEF VALVE
Location – A duct relief valve is located downstream of the NRV.
Function – The function of this valve is to protect the duct from over pressurization.
There is a real danger that if the duct ruptures, high temperature air could play onto
fuel lines or electrical cables and start a fire.
The relief valve is set to operate at 10 psi above the ducts normal pressure. The
standard used in examination questions is the valve’s vale (10 psi).
CHOKE VALVE AND DUAL PRESSURE SWITCH
The choke valve is fitted as a means of increasing the charge air’s temperature in
certain conditions, by restricting the flow and creating a backpressure. The choke
valve only restricts the airflow when the bypass valve downstream is fully open.
BYPASS VALVES
There are two bypass valves fitted in this system,
Location 1 – one downstream of the choke valve
Location 2 – second downstream of the primary heat exchanger.
They function as temperature control valves.
Function 1 – The first bypass valve can direct all the air through the heat exchanger
or allow a percentage of air to bypass the heat exchanger.
Function 2 – The second valve control the amount of air that enters the CAU.
Both valves are controlled by temperature sensors, either mounted in the
aircraft’s cabin or in the duct leading into the aircraft’s cabin.
PRIMARY HEAT EXCHANGER
The system has two heat exchangers, which act as radiators. Charge air from the
first bypass valve is ducted into the primary heat exchanger, also known as a pre-
cooler. In the heat exchanger, the hot charge air is passed through a matrix of small-
bore pipes, while ram ambient air passes around them. As the heat exchanger is
open ended, this results in adiabatic cooling, where the temperature decreases, but
there is no significant change in the pressure.
BOOTSTRAP
The bootstrap consists of three components in the following order: compressor,
heat exchanger, and turbine.
The compressor and turbine are linked together and form one CAU.
The system is referred to as a bootstrap as it is able to self-start. As soon as there is
air flowing across the turbine, it starts to revolve itself and the compressor.
Due to the compression and work done by the cold air unit and the speed of rotation,
these units must be lubricated. Failure of the oil seals can result in blue smoke
entering the cabin.
Air that has been cooled by the pre-cooler is directed by the second bypass valve
into the eye of the CAU’s centrifugal compressor.
AT COMPRESSOR Here, it is compressed, raising both pressure and temperature.
The output from the compressor is then passed through the secondary heat
exchanger, also referred to as an intercooler, before being ducted on to the edge of a
turbine.
In the turbine, the air is made to work by rotating the turbine and compressor.
The work absorbs pressure energy and, at the same time, the air is able to expand.
The combined effect reduces the temperature of the air, resulting in a stream of cold
air leaving the turbine.
The speed of the CAU is determined by the temperature requirements of the system
and the air’s density. The lower the temp. selected from the flight dock the more is
speed of CAU.
WATER EXTRACTOR
Excess humidity inside the aircraft would manifest itself as condensation or even
water droplets failing from the air conditioning low-pressure ducts. This would lead to
discomfort for the passengers and crew, as well as the possible shorting of electrical
circuits, corrosion, and an increase in mass over time as the insulation blankets
become sodden.
LOCATION – To remove this excess moisture, water extractors, also known as water
separators, are fitted downstream of the cold air unit.
There are different designs of water extractors. However, they all work on the same
basic principle of diffusion, coalition, and extraction. As the air enters the water
extractor, it passes through a diffuser section that slows the airflow and guides it over
a coalesce section.
Here, the moisture is coalesced (merged) into larger droplets.
HUMIDIFIER
In aircraft operating at high altitudes (greater than 40,000 feet) for long periods of
time it may be necessary to increase the moisture content of the conditioning air to
1-2% relative humidity to prevent physical discomfort arising from low relative
humidity. This is the function of the humidifier, a typical example of which is shown
below. The aircraft’s drinking water supply is used and the water is atomized by air
from the air conditioning supply.
Bootstrap used in conjunction with bleed air from a gas turbine engine. Turbine
powered aircraft, where the compressor section can supply more air than the core
engine requires, are able to supply bleed air to the packs.
This air has been heated due to compression. Therefore, in this system, there is no
requirement for a blower and silencer.
In the event of any problem, the bleed air to the air conditioning back can be cut by
closing the bleed air shut off valve (SOV). This isolates the engine, and as the air
entering the engine passes through it, there is no need for a spill valve.
A mass flow controller linked to a flow control valve ensures that the correct mas of
air is supplied to the system as the aircraft changes altitudes and engine rpm
settings.
Restriction creates back pressure on the compressor & put the load on turbine. This
makes RPM self regulating in these machines.
BE
In this system, the bleed air is passed through a pre-cooler to obtain adiabatic
cooling and then to a temperature control valve, or TCV. This directs the precooled
air to the turbine or plenum chamber. To ensure that the air passing across the
turbine loses pressure and temperature, a compressor draws in ambient air at static
pressure by taking its supply from within a vented bay. This air passes across the
compressor and is dumped overboard via a restricted pipe.
The restriction creates a backpressure that acts to slow the compressor and place a
load on the turbine. The speed of these machines is self-regulating and is
determined by the mass of air that passes across the turbine and the air’s density.
They can be turning at 40,000 rpm at high altitude.
In these systems, if hotter air is required in the system, the bleed air can be taken
from latter stages of compression in the engine. As before, the streams of air are
mixed in a plenum chamber before passing into the aircraft cabin.
This system is lighter (only one heat exchanger) and the mass flow/weight
ratio.
FAN TURBINE (TURBO-FAN)
This is a refinement of the brake turbine unit, in which, instead of a compressor, the
turbine is coupled to a fan of sufficient capacity to draw the required volume of
cooling airflow through the primary heat exchanger so that the unit is not dependent
on ram air for its operation and can therefore be operated on the ground.
ok
VAPOUR CYCLE (REFRIGERATION) SYSTEM :
The vapour cycle air conditioning system is similar in operation to the domestic
refrigerator or the galley cart cooling system used on some large aircraft. Its use for
aircraft is now generally limited to small piston engine types.
B
A refrigerant is used to absorb heat from the charge air by changing its state from
liquid to gas. The heat is carried by the refrigerant to a condenser where it is given
up to the atmosphere and the refrigerant returns to its liquid state.
** In the vapour cycle system the refrigerant alternates between the vapour and
liquid phase. It is compressed, cooled, expanded and heated in that order. The
refrigerant is a liquid (Freon) which boils at approx. 3.5°C (38°F) at sea level
atmospheric pressure.
**At higher pressure the boiling point is increased and vice versa.
Working
Refrigerant at low pressure is drawn through the evaporator by the compressor
(which may be electrically or air driven). As it passes through the evaporator the
refrigerant changes state from liquid to gas absorbing heat from the cabin air supply
and therefore cooling the air as it does so.
The COMPRESSOR raises the pressure and therefore the boiling point of the
refrigerant before it enters the condenser.
The CONDENSER is positioned so that cold ram air passes over it and the
refrigerant changes back to its liquid state giving up latent heat to the ram air. The
pressurized liquid then passes to the receiver which acts as a reservoir and then
through an EXPANSION VALVE which reduces its pressure and boiling point before
entering the evaporator to repeat the cycle.
RE-CIRCULATION FANS
These augment the air conditioning packs allowing the packs to be operated at a
reduced rate during the cruise which decreases engine bleed requirements and
maintains a constant ventilation rate throughout the cabin.
The fans draw cabin air from the under floor area through filters then reintroduce the
air into the Mix manifold conditioned distribution system where it is mixed with fresh
air from the packs and resend to the cabin. Air from the region of toilets and galleys
is not re-circulated but is vented directly overboard by the pressurization discharge
valves.
TEMPERATURE CONTROL
RAM AIR MUFFLER TYPE HEAT EXCHANGER
In these systems, which are used in unpressurised piston engine aircraft, ambient
atmospheric air is introduced to the cabin through forward facing air intakes. Some
of this ram air can be heated by exhaust or combustion heaters and then mixed with
the cold ambient air in varying proportions to give a comfortable cabin temperature.
Whenever cabin heat is used it is used in conjunction with the use of fresh air.
A leak in the exhaust pipe may cause pilot incapacitation due to carbon monoxide
poisoning.
BB
The heater muff or exhaust muff is a close fitting cowl around the exhaust pipe which
allows ram air to come into close contact with the hot exhaust pipe to provide hot air
for heating the cabin. Fresh cold air can be allowed into the cabin through the ram
air inlets on the wing leading edge. After use the air is dumped overboard through a
vent on the underside of the aircraft.
COMBUSTION HEATER
More sophisticated light aircraft can use a dedicated combustion heater to heat ram
air. The fuel used in the heater is normally that which is used in the aircraft’s
engines and the heater works by burning a fuel/air mixture within the combustion
chamber. Air for combustion is supplied by a fan or blower and the fuel is supplied
via a solenoid operated fuel valve.
The fuel valve is controlled by duct temperature sensors but can be manually
overridden. The system is designed so that there is no possibility of leaks from
inside the chamber contaminating the cabin air. In addition the system must be
provided with a number of safety devices which must include:
a) Automatic fuel shut-off in the event of any malfunction.
b) Adequate fire protection in the event of failure of the structural integrity of the
combustion chamber.
c) Automatic shut-off if the outlet air temperature becomes too high.
PRESSURISED AIRCRAFT
For larger and faster pressurized aircraft, it is standard to fit two air conditioning units
(referred to as air conditioning packs, abbreviated to ACS packs of just packs) to
serve the system. This allows for redundancy, as one pack is able to maintain the
minimum conditions required by the regulation.
OXYGEN SYSTEM
RAPID DECOMPRESSION
A rapid decompression occurs when the cabin pressure decreases to ambient in a
period of 5 to 7 seconds.
As the pressure drops, air and gases within the body expand and rush to
atmosphere. Normally, air rushes from the mouth and nasal passages, allowing the
lungs and middle ear to equalize.
The main danger is hypoxia. Unless rapid utilization of the aircraft’s supplementary
oxygen system is made, unconsciousness occurs. This is done by the Oxygen
system of the Aircraft.
If the flight crew believe that they are in danger of a decompression (cracked
windscreen, etc.) they must place themselves on oxygen, initiate a let-down, and
raise the cabin altitude to minimize the differential to reduce the effect of any
subsequent decompression.
If an aircraft suffers decompression at high altitude, the maximum rate of descent
that the crew can ever initiate is Vd or dive velocity.
The 10,000 ft audible and visual warning occurs to alert the crew of possible
problems, so that they have time to correct where possible, to minimize passenger
discomfort and possibly to prevent passenger oxygen masks from dropping.
If the problem cannot be solved, the pressure controller signals the outflow valves to
close to minimize the loss of cabin pressure.
If the cabin altitude reaches 14000 ft, the passenger oxygen masks that are stored in
the passengers’ overhead service unit (PSU), are deployed to the half-hung position
by a barostatic controller. This is done at this altitude to ensure that supplementary
oxygen is available before the cabin reaches 15000 ft.
These extra masks are to enable cabin crew or passengers who are away from their
seats to gain immediate access to oxygen. As crew or passengers might be in the
aircraft lavatories when oxygen is required, each aircraft lavatory must have two face
masks.
OXYGEN
In aviation, there are three physical states for three physical states for the
transportation of oxygen:
Liquid
Gaseous
Chemical
Liquid oxygen is not used in the civil aviation industry, as it is very expensive and
poses handling, storage, and safety problems. Flight crew are always supplied with
gaseous oxygen, as this is the most economic and effective way to meet the
regulations.
The continuous flow system is normally used in light un-pressurised aircraft intending
to fly above 10000 ft, or as the passenger supplementary oxygen system for some
pressurized aircraft. The diluter demand system, a more sophisticated and more
expensive system, is used for flight crew of air transport aircraft.
In these systems, gaseous oxygen stored in a cylinder at 1800 psi is passed through
an intermediate pressure regulator, where the pressure is dropped to between 80-
100 psi. It is then fed into a ring main or manifold. A barometric valve prevents the
oxygen from flowing to the passenger masks.
When the cabin altitude exceeds 14000 ft, the barometric valve opens and allows
oxygen to pass into the low-pressure regulator. At the same time, pneumatic
pressure opens a latch allowing the PSU door to open and deploy the masks in the
half-hung condition. The act of pulling the face mask down opens the valve to the
mask, allowing continuous flow of oxygen into a one-size fits-all rubber cup that
covers the mouth and nose and has an elasticized head
The masks are stowed in the passenger service units (PSU), the doors of which will
open automatically by a barometrically controlled release mechanism if the cabin
altitude reaches 14000 ft or by manual selection from the flight by the crew at any
altitude below this.
This release mechanism is actuated electrically for the chemical generator system
and pneumatically for the gaseous system.
When the PSU doors open the masks drop to the “half-hung” position.
Pulling the mask towards the face initiates the oxygen flow by opening a check
valve on the gas supplied system or operating the electrical or percussion cap firing
mechanism on the chemical generator.
The generators are located in each passenger, cabin attendants and lavatory service
units.
The sodium chlorate and iron core is shaped to provide maximum oxygen flow at
starting.
A filter in the generator removes any contaminates and cools the oxygen to a
temperature not exceeding 10°C above cabin ambient temperature.
A relief valve prevents the internal pressure in the generator exceeding 50 psi, the
normal flow pressure is 10psi. Sufficient oxygen is supplied form the generator to
meet the requirements to descent in emergency conditions. (min of 15 mins).
Caution.
Once the chemical reaction has started, it cannot be stopped.
Surface temperatures of the generator can reach 232°C (450°F)
A strip of heat sensitive tape or paint changes colour, usually to black, when the
generator is used and provides visual indication that the cylinder is expanded.
Chemical generators have a shelf life to ten years.
Oxygen is diluted with air and supplied as demanded by the users respiration cycle
and the oxygen regulator.
The differential created biases the diaphragm across to the right. The bow spring,
oxygen pressure acting on the demand valve, and the demand valve’s spring limit its
movement.
It is usually possible to set one of two flow rates depending on requirement. These
are Normal and High which correspond to flow rates of 2 and 4 litres per minute.
SAFETY PRECAUTIONS
The following general safety precautions apply to all oxygen systems.
a. Oxygen is a non-flammable heavier that air gas which supports combustion as
well as life. Any flammable material will burn more fiercely in the presence of
oxygen than in air. Smoking is therefore banned in oxygen rich atmospheres.
b. No oil or grease should be allowed to come into contact with oxygen as there
is the possibility of a severe chemical reaction.
c. Any moisture present will react with gaseous oxygen and can cause corrosion
and the possibility of valves freezing.
d. During replenishment or maintenance of oxygen systems the surrounding
area must be adequately ventilated. Remember that oxygen is heavier than
air and will fill low lying areas such as servicing pits, aircraft bilges, etc.
e. Only lubricants specified in the maintenance manuals may be used. E.g.
graphite.
SUMMARY
Advantage of AC over DC
1. Ease with which AC can stepped up and step down efficiently wing a
transforms,
2. Lighter and thin cable in AC
3. Less arcing and sparking in AC
4. More reliable but high altitude & high RPM
▪ Resistance in parallel :- Is the sum of the reciprocals of individual resistance
▪ Resistance in series :- Sum of the individual resistance.
ELECTRICITY
There are basic means to provide the force which causes electrons to flow:-
a) Friction – static electricity
b) Chemical action – cells and batteries (primary and secondary cells)
c) Magnetism – generators and alternators
d) Heat – thermocouples (junction of two dissimilar metals)
e) Light – photo electric cell
f) Pressure – piezo electric crystals
In the same way that water needs a force (pressure) to make it flow, electricity needs
pressure, Electro Motive Force (EMF), to make it flow.
EMF is measured in units of Voltage. The number of volts is a measure of the EMF
or potential Difference (the difference in electrical potential between the positive and
negative terminal). Voltage is given the symbol V or E.
RESISTANCE
The obstruction in the circuit which opposes the current flow is called resistance.
Different materials have different numbers of free electrons, those with more free
electrons will have a lower resistance than those with few free electrons, so those
with more free electrons are better conductors of electricity.
UNITS OF RESISTANCE
The unit of resistance is the Ohm (symbol n) A material has a resistance of one ohm
if an applied voltage of one volt produces a current flow of one ampere.
RESISTORS
Sometimes resistance is used to adjust the current flow in a circuit by fitting resistors
of known value. Could be of two types fixed and variable resistors.
OHMS law:
V=IR
If the resistance remains the same any increase in voltage will cause an increase in
current and vise versa (Current directly proportional to voltage).
POWER
When a force produces a movement then work is said to have been done, the rate at
which work is done is called power.
● Fuses and CB’s are fitted in both AC and DC Circuits.
● Fuses and CB (Circuits Breaker) are connected in series with the loads.
● Fuses & CB are rated in AMPS.
● CB works as a sweeter as well as a fuse.
● In an open circuit Resistance is Maximum (INFINITE) (Cause its not lefting
any single current to pass).
● Fuse works on a principal of a low melting ALLOY.
● A circuits of 6V and 2Ohms resistance will require a Fuse of
A. 5 AMPS
B. 3 AMPS
C. 1.5 AMPS
= Force × Velocity
= Volt × I
P = IR × I
In an electric circuit work is done by the Voltage causing the current to flow through
A resistance, creating heat, magnetism or chemical action.
The rate at which work is done is called Power and is measured in Watts
Watts(W) = Voltage (V) × Amperes (I)
Fuses are made of a type of wire which has a low melting point, and when it is
placed in series with the electrical load it will melt, blow or rupture when a current of
higher value than its ampere rating is placed upon it. Fuses are rated in ‘amps’.
CURRENT LIMITERS
Current limiters, as the name suggests, are designed to limit the current to some
predetermined amperage value.
They are also thermal devices, but unlike ordinary fuses they have a high melting
point, so that their time/current characteristics permit to carry a considerable
overload current before rupturing.
For the reason their application is confined to the protection of heavy duty power
distribution circuits. The output of a Transformer Rectifier Unit would be a prime
location for a current limiter to be used.
CIRCUIT BREAKERS
Circuit breakers combine the function of fuse and switch and can be used for
switching circuits on and off in certain circumstances.
Circuit breakers are common on the flight deck of modern aircraft and can be
categorized as either:-
a) A Non-Trip Free Circuit Breaker, or
b) A Trip Free Circuit Breaker (image)
The non-trip free circuit breaker may be held in under fault conditions and the circuit
will be made, this is clearly dangerous.
The Trip free circuit breaker if held in under the same circumstances the circuit can
not be made.
CAPACITORS
A capacitor can perform three basic functions:
1. Store an electrical charge by creating an electric field between the plates.
2. Will behave as if it passes Alternating Current
3. Blocks Direct Current flow
Construction:
In its simplest form a capacitor consists of two metal plates separated by an insulator
called a dielectric. Wires connected to the plates allow the capacitor to be
connected into the circuit.
CAPACITANCE
A capacitor (C) of a capacitor measures its ability to store an electrical charge. The
unit of capacitance is the FARAD (F). The farad is subdivided into smaller, more
convenient units.
CAPACITOR
● Capacitor provides initial current flow whenever any electrical service is
selected
● Capacitor’s doing a same job as accumulator in Hydraulics
● Capacitors are used in ignition circuit of a Piston and JET engine.
● JET Engine spark plug works on a principle of capacitor discharge
CAPACITOR IN A DC CIRCUIT
A capacitor in series with a battery and a switch
After a short time the difference in charge between the plates results in a potential
difference existing between the plates. The flow of electrons will reduce and stop
when the potential difference between the plates is equal to the supply voltage. The
capacitor is now fully charged, current has stopped flowing, the plates are said to be
charged and there exists an electric field between the plates. The capacitor is now is
fully charged, current has stopped flowing, the plates are said to be charged and
there exists an electric field between the plates. The capacitor is now blocking DC
flow. The capacitor will only discharge if it is now connected to an external circuit.
CAPACITORS IN PARALLEL
Capacitors connected in parallel are effectively increasing the area of the plates.
The total capacitance Ct can be found by adding the individual capacitance:
CAPACITORS IN SERIES
Capacitors in series have effectively increased the distance between the plates and
therefore the total capacitance has decreased. The total capacitance is found by
using the formula for resistances in parallel:
BATTERIES
A battery is made up of one or more cells which convert chemical energy to electrical
energy
PRIMARY CELLS are of type that is normally used in torches and transistor radios.
A fully charged Primary Cell gives rise to a potential difference of 1.5 Volts. Once
discharged, Primary cells cannot be recharged. A primary cell consists of two
electrodes immersed in a chemical called an electrotype. The electrolyte
encourages electron transfer between the electrodes until there is a potential
difference between them.
The capacity of a cell is a measure of how much current it can provide over a certain
period of time.
In aircraft batteries, cells are usually connected in series with other cells of the same
voltage and capacity. The presentation shows a battery with six cells, connected in
series.
SECONDARY CELLS work on the same principle as primary cells but the chemical
energy in the cell can be restored when the cell has been discharged by passing a
“charging current” through the cell in the reverse direction to that of the discharge
current. The capacity of a cell is a measure of how much current a cell can provide
in a certain time. Capacity is measured in Ampere hours (Ah)
One of the most common types of secondary cell is the Lead Acid Cell.
The active material of the positive plate is lead peroxide and the negative plate is
spongy lead, both plates are immersed in an electrolyte solution of water and
sulphuric acid.
The lead acid battery is the most commonly used in light aircraft. The electrolyte of a
fully charged cell will have a specific gravity of approx. 1.3. The specific gravity of
the electrolyte can be measured with a HYDROMETER.
SUMMARY
▪ Battery are charged at a constant voltage varying current (CVVC)
▪ Overheating of battery may take place due to charging the battery at a constant
current more than capacity
▪ A/c battery are checked every 3 months
▪ Before flight battery capacity should be 80%
▪ Light aircraft battery is normally 24 volts
▪ More than one battery in a/c will be connected in parallel
▪ Cells in a battery are connected in series
▪ Vent in a battery exhaust the gasses out formed while charging
▪ A fully efficient battery 60 amph can give 6 amperes for 10 hours.
▪ Battery voltage is checked on load with all circuits switched on by a voltmeter
▪ S.G. 1.3 charged and S.G. 1.17 discharged checked using hydrometer.
TEMPORARY MAGNETS
Temporary magnets are made from soft iron which is easily magnetized but readily
loses its magnetic properties.
▪ With time and use battery’s voltage and current reduces.
▪ Battery converts chemical energy to electrical energy.
PERMANENT MAGNETS
Permanent magnets are made from hard alloy steels which are difficult to magnetise
but retain their magnetism well.
THE MAGNETIC FIELD OF A SOLENOID
A solenoid (electromagnet) is a coil of a large number of turns of insulated wire.
THE STRENGH OF THE FIELD OF A SOLENOID
The strength of the field of a solenoid can be increased by:
a. Increasing the number of turns on the coil
b. Increasing the current
c. Using a soft iron core.
When the current is switched off the magnetic field collapses leaving a little residual
magnetism in the soft iron core.
attracted armature.
ELECTROMAGNETIC INDUCTION
Batteries are a good source of DC electricity by conversion of chemical energy, but
they are not inexhaustible and will go flat after a period of time and need recharging.
The primary source of electricity in an aircraft is always the generator or alternator.
Magnetism can be used to generate electricity by converting mechanical energy to
electrical energy by Electromagnetic Induction.
If a conductor is moved in a magnetic field the conductor will ‘cut through’ the
invisible lines of flux. When this happens an Electromotive Force EMF (voltage) is
induced into the conductor as long as the conductor keeps moving. If the conductor
stops the induced EMF ceases. It does not matter if the conductor or the magnetic
field is moved as long as there is relative movement between the two.
FARADAY’S LAW
Farady’s law states:-
When the magnetic flux through a coil is made to vary, a voltage is set up. The
magnitude of this induced voltage is proportional to the rate of change of flux.
SIMPLE GENERATOR
The rotating loop is known as the armature.
The magnetic field is termed the field.
In a simple generator the armature rotates in the field.
An EMF is induced in the armature by electromagnetic induction.
The alternator has a much better power to weight ratio, will produce a stable output
at low RPM and does not suffer with the problems of a commutator as it uses a
rectifier to convert AC to DC.
DC GENERATOR ALTERNATOR
DC GENERATOR OUTPUT RATING is in ALTERNATOR OUTPUT RATING.
Kilo Watts (Kw) Alternator is rated in Volt Amperes (VA)
or Kilo Volt Amperes (KVA), the Apparent
Power.
Rotating Armature Stationary Armature
Stationary Field Rotating Field
Converts AC to DC by means of a Converts AC to DC by means of a
commutator rectifier
Suffers from arcing and sparking at the High load current taken from stationary
commutator as the high load current has armature eliminates arcing and sparking.
to flow through the commutator and
brushes
VOLTAGE CONTROL
µ
Most light aircraft DC electrical systems operate at 14 volts and so all the equipment
it designed to operate correctly when supplied with 14 volts. It is therefore
necessary for the output of the generator or alternator to be controlled, or regulated,
to ensure that at all times it supplies 14 volts.
The generator or alternator is driven by a drive belt or an engine accessory gearbox
and therefore the speed of rotation of the armature or field is linked to the speed of
rotation of the engine.
Controlling the output voltage by controlling the speed of the engine is not a practical
solution.
The only practical method of controlling the output voltage of a generator is to control
the strength of the magnetic field by controlling the current flow in a coil wound
around the magnetic pole pieces (field coil or field winding). Control of the current
flow is achieved by a voltage regulator.
A voltage regulator consist of:-
a) A variable resistance in series with the field coil. DC generator
b) A control coil in parallel with the field coil and the armature. AC generator
The voltage regulator senses the output voltage of the generator or alternator and
adjusts the field current to maintain the correct output voltage irrespective of
generator speed or electrical load.
AIRCRAFT ELECTRICAL POWER SYSTEMS
The power system for a single-engine aircraft consists of a generator or alternator
with the control and indication equipment necessary to supply all the electrical power
once the system is on-line.
The term on-line means that the generator or alternator has been switched into the
electrical system and is actually supplying power to the system.
With multi-engine aircraft two or more generators or alternators are installed in
parallel. The ampere capacity of an aircraft electrical system is determined by the
number of power-consuming devices fitted.
DI-POLE OR TWO WIRE SYSTEM
A dipole or two wire system is required where an aircraft is made of a nonconductive
material.
The current needs a complete circuit to flow and therefore needs a negative wire to
connect the load to the negative side of the generator as well as a positive or ‘live
wire’ to connect from the Bus bar (distribution point) to the load.
If, With the engine running, the pointer of the Centre Zero Ammeter is well into the
negative sector of the dial, it must be deduced that the alternator has failed and is
not supplying the electrical loads and the battery is discharging. In this case you
should switch off any unnecessary electrical services.
If during flight the Load Meter reading remains high, this may indicate that the battery
is recharging at too high a rate. This will damage the battery and cause it to
overheat.
If the electrons flowing in a circuit move backwards and forwards about a mean
position then the current produced is known as Alternating current (AC).
This means that to produce constant 400H2 electricity the RPM of the alternator
meant be constant at 8000 RPM.
But how to keep the frequency of an alternator at 400Hz. This is achieved by CSDU
Alternating current (AC) is used in most large modern transport aircraft because of
the following advantages that it holds over direct current.
❖ AC generators are simpler and more robust in construction than DC
❖ The power to weight ratio of AC machines is better than comparable DC
machines.
❖ The supply voltage can be converted to a higher or lower value with almost
100% efficiency using transformers.
❖ Any required DC voltage can be obtained simply and efficiently using
transformer rectifier units. (T.R.U.s)
❖ Three phase AC motors which are simpler, more robust and more efficient
than DC motors, can be operated from a constant frequency source, (AC
generators).
AC machines do not suffer from the commutation problems associated with DC
machines and consequently are more reliable, especially at high altitude.
AC CURRENT TERMINOLOGY
CYCLE – A cycle is one complete series of values.
PHASE – A sine wave can be given an angular notation called phase. One cycle
represents from 0°-360° of phase
FREQUENCY – The number of cycles occurring each second is the frequency of the
supply. The frequency is measured in Hertz (Hz). One cycle per second is equal to
one Hertz. Constant frequency AC supply systems usually have a frequency of 400
Hz. For modern a/c system.
Frequency is dependent upon the number of times a North and a South pole pass
the armature in a given time period.
For example, an 8 pole generator rotating at 6,000 R.P.M. will have an output
frequency of :-
ANS : 400 Hertz
The INDUSTRY STANDARD that has evolved for constant frequency aircraft is:
(DGCA)
115/200v AC, 3 phase, 400 Hz.
The currents and voltages generated in this type of machine will have the same
frequency but be out of phase with each other, the phase windings are mechanically
arranged to be at 120° to each other in the sequence A,B, C so that the outputs are
electrically separated by 120°. It can be seen that “A” phase reaches a peak going
positive before “B” phase reaches a peak going positive before “C” phase reaches a
peak going positive. This is the phase sequence ABC.
The ADVANTAGES of a three phase system are :-
a. They have a greater power/ weight ratio
b. They are easier to work in parallel
•
•
CONSTANT FREQUENCY ALTERNATORS
For A/c Systems to work constant frequency AC is needed but the question is how to
keep the frequency constant?
If the alternator can be driven at a constant speed, then the output frequency will be
constant.
Driving the engine at a constant speed is not a practical proposition so a device is
required to keep the speed of the alternator constant irrespective of the engine
speed.
The output of the hydraulic pump, and therefore the speed of the hydraulic motor,
depends on the angle of a swash plate (constant pressure Pump) within the pump.
The angle of the swash plate is controlled by a device called a speed governor.
The speed governor is controlled by the load controller which senses the output
frequency of the alternator and is responsible for increasing or decreasing the torque
output of the C.S.D.U. to the alternator drive.
Most C.S.D.U. are capable of maintaining the alternator output frequency within 5%
of 400 Hz (380-420 Hz).
The CSDU operates in one of three modes overdrive, straight through drive or under
drive.
Overdrive = engine speed less than generator speed
Straight through drive = engine speed same as generator speed
Under drive = engine speed greater than generator speed
Some constant frequency generators have their CSDU and generator combined in
one unit called an Integrated Drive Unit (IDU) or Integrated Drive Generator (IDG)
DGCA – PLS remember Battery is getting charged through a TRU in Series. And is
parallel to the AC generator
This “load sharing” or “paralleling” requires that two parameters are regulated:-
1. REAL LOAD
Real Load is the actual working load output available for supplying the various
electrical services and it is measured n Kilowatts (real power or true power)
Real Load Sharing is achieved by controlling the Constant Speed Drive Unit
(C.S.D.U.)
2. REACTIVE LOAD
Reactive Load is the so-called Wattless Load which is the vector sum of inductive
and capacitive currents and voltages expressed in KVARs (Kilo Volt-Amperes
Reactive).
Reactive Load Sharing is achieved by controlling the Voltage Output (Exciter Field
Current) of each generator that is connected in parallel.
TRANSFORMERS
One of the biggest advantages that an AC supply has over a DC supply is the ease
with which the value of alternating voltage can be raised or lowered with extreme
efficiency by the use of Transformers.
A simple transformer would consist of two electrically separate coils wound over iron
laminations to form a common core.
B
If the transformation ration is greater than one, then the transformer is a Step Up
transformer. If the ratio is less than one, then the transformer is a Step Down
transformer.
The A.P.U. alternator cannot normally be paralleled with the engine driven
alternators, and will usually only supply power to the bus bars when no other source
is feeding them.
INVERTERS
An inverter converts DC to AC.
The inverter in an constant frequency AC equipped aircraft is used as a source of
emergency supply if the AC generators fail, then the inverter is powered by the
battery. Inverters are invariably “solid state” static inverters, (transistorized), in
modem aircraft providing constant frequency AC for operation of flight instruments
and other essential AC consumers.
BONDING
An aircraft in flight will pick up, or become charged with, static electricity from the
atmosphere.
Bonding will prevent any part of the aircraft from building up a potential so great that
it will create a spark and generate a fire risk.
Each piece – of the metal structure of the aircraft, and each component on the
aircraft, is joined to the other by flexible wire strips.
This process is called bonding, and it provides an easy path for the electrons from
one part of the aircraft to another.
SCREENING
Screening is designed to prevent radio interference by absorbing electrical energy.
Static electrical charges, produced by the operation of certain electrical equipment,
create interference on radio circuits.
STRUCTURE
2. MONOCOQUE CONSTRUCTION
‘Monocoque’ is a French word meaning ‘ single shell’. In a monocoque structure.
All the loads are taken by a stressed skin with just light internal frames or
formers to give the required shape. Formers also help the A/C to withstand hoop
stress which arises because of the pressurization cycle
3. SEMI-MONOCOQUE CONSTRUCTION
q
As aircraft became larger, the pure monocoque was found not to be strong enough.
Longerons run length wise along the fuselage joining the frames together. The light
alloy skin is attached to the frames and longerons by riveting or adhesive bonding.
Remember : Longerons are also called as Stringers (Stiffeners) Function- Stiffens
the skin and assist the sheet materials to carry loads along their length.
Bulkheads isolate different sections of the aircraft, for instance the engine
compartment from the passenger compartment. Bulkheads are of much stronger
construction than fames or formers, as the loads upon them are so much greater.
Construction of Wing
Remember that energy control surface is attached to the rear spar. The front
spar is the main spar.
Lighting Hole in a RIB is lighten the structure wing with fuel cell in it is known as
wet wing.
From star, near spar, ribs & skin forms a torsion box which is highly resistant to
bending and twisting.
Bread monoplane :- wings are supported at more than one points by Fuselage
Cantilever Monoplane – only connected to fuselage at a point via bots and no other
support
BI-PLANE CONSTRUCTION
For biplanes which fly less than 200 kts in level flight, so a truss type design is
adequate. The bracing wire form of great rigidity which is highly resistant to bending
and twisting. Large amounts of drag are produced, hence lower airspeeds.
CANTILEVER MONOPLANE
A cantilever structure would consist of a front and rear spar, with the metal skin
attached to the spars to forma torsion box.
The stringers are spanwise members which give the wing rigidity by stiffening the
skin in compression.
Formers, or ribs, maintain the aerofoil shape of the wings. They support the spars,
stringers and skin against buckling, and pass concentrated loads from engines,
landing gear and control surfaces into the skin and spars.
Tension
A tension, or tensile, load is one which tends to stretch a structural member.
Components designed to resist tensile loads are known as ties.
Compression.
Compressive loads are the opposite of tensile loads and tend to shorten structural
members. Components designed to resist compressive loads are known as Struts.
Shear
Shear is a force which tends to slide one face to the material over an adjacent face.
Rivetted joints are designed to resist shear forces.
COMBINATION LOADINGS
Bending
Torsion
Torsion or twisting forces produce tension at the outer edge, compression in the
centre and shear across the structure.
Stress
Stress is the internal force inside a structural member which resists an externally
applied force and, therefore, a tensile load or force will set up a tensile stress,
compression loads compressive stresses etc.
Strain
When an external force of sufficient magnitude acts on a structure, the structural
dimensions change. This change is known as strain and is the ratio of the change in
length to the original length and is a measure of the deformation of any loaded
structure.
Buckling
Buckling occurs to thin sheet materials when they are subjected to end loads and to
ties if subjected to compressive forces.
COMPOSITE MATERIALS
Composite materials are manufactured from reinforcing fibres embedded in a
bonding resin. As the materials can be moulded, they are described as plastic.
Magnesium alloys are also used, their principal advantage being their weight. This
gives an excellent strength to weight ratio (aluminium is one and a half times
heavier). The elastic properties of magnesium are not very satisfactory so its use in
primary structures is limited.
Aluminium and its alloys are the most widely used metals for structural use due to a
good strength to weight ratio with ‘duralumin’ type alloys predominating due to their
good fatigue resistance.
Steel and its alloys used where strength is vital and weight penalties can be ignored.
When aluminium is alloyed with 4% copper (Al-Cu) the resulting alloy has a lower
strength-to weight ratio, a good fatigue reistance and is easier to use in
manufacturing since it is softer than Al-Zn alloys. This material is often called
Duralumin and is extensively used in Production of Aircraft.
SAFE LIFE
The aircraft structure, as a whole, and components within the aircraft are given a
safe life. This is based on one, several, or all of the following:
● Cumulative flying hours
● Landings
● Pressurisation cycles
● Calendar time
FAIR-SAFE STRUCTURE
Fail-Safe
To achieve a fail-safe structure, no one item within a structure takes the entire load.
It is shared by several components, thus there are multiple load paths. This
redundancy of items allows the structure to continue operating normally up to the
static ultimate for a limited period. These are not preferred due to the fact it is
difficult to find out the damage occurrence are a in the structure. Therefore A
programmed inspection is required.
Speed brakes are devices to increase the drag of an aircraft when it is required to
decelerate quickly or to descent rapidly. To operate them as speed brakes they are
controlled by a separate lever in the cockpit and move symmetrically. Spoilers
functions as a roll control whilst being used as speed brakes, by moving
differentially from the selected brake position.
Oleo-pneumatic Struts. Some fixed main under carriages, and most fixed nose
undercarriages, are fitted with an oleo-pneumatic shock absorber strut.
Spats are an aerodynamic fairing which may be required to minimize the drag of the
landing gear structure.
The outer cylinder is fixed rigidly to the airframe structure by two mounting brackets,
and houses an inner cylinder and a piston assembly, the interior space being
partially filled with hydraulic fluid and inflated with compressed gas (air or nitrogen).
DIFFERENTIAL BREAKING
Is when Pilot apply more break pressure on one side of the wheel & less Px on other
side to turn aircraft in confined spaces.
An undercarriage unit has to withstand varying loads during its life. These loads are
transmitted to the mountings in the aircraft structure, so these too must be very
strong. The loads sustained are;
a. Compressive (Static and on touch down)
b. Rearward bending. Due to forward movement
c. Side (During cross wind landings, take offs, and taxying).
d. Forwards (during push back).
e. Torsional (Ground Manoeuvring).
NOSE UNDERCARRIAGE
A nose undercarriage unit, is usually a lighter structure than a main unit since it
carries less weight and is usually subject only to direct compression loads. Its
design is complicated by several requiremens.
a. Castoring
b. Self centring
c. Steering
d. Anti-shimmy
Castoring is the ability of the nose wheel to tum to either side in response to the
results of differential braking or aerodynamic forces on the rudder.
SELF CENTERING
Automatic self centering of the nose wheel is essential prior to landing gear
retraction. If the nose gear is not in a central position prior to its retraction, the
restricted space available for its stowage will not be sufficient and severe damage
may be caused.
To allow free castoring of the nose undercarriage when required, i.e. towing, a by-
pass is provided in the steering system hydraulics to allow fluid to transfer from one
side to the other.
Cause of Shimmy
1. Broken torque link
2. Over inflated tyre- If air Px is more, then shimmy is more.
3. Wear in the wheel bearing or work shimmy damper.
Steering Operation
Normal nose wheel steering operating pressure is derived from the undercarriage
‘don’ line, and a limited emergency supply is provided by a hydraulic accumulator,
hydraulic pressure passes through a CHANGE-OVER VALVE, which ensures that
the steering system is only in operation when the nose undercarriage is down.
Excessive shimmy, especially at high speeds, can set up vibrations throughout the
aircraft and can be dangerous.
OPERATIONS
FUNCTION OF SEQUENCE VALVE
When the Nose undercarriage is fully retracted it is retained in position by the NLG
Uplock (Hydraulically released-Spring applied).
The one way restrictor (Restricted Flow) which restricts the rate of fluid return acting
as a door speed damper.
LIGHT INDICATIONS
1. Green light is only shown for one reason L.G. Down & Locked
2. Red light shown for many up not locked. Down, not locked, In Transit.
The electrical undercarriage system operates in such a manner that green light is
displayed when the undercarriage is locked down, a red light is displayed when the
undercarriage is in transit, and no lights are visible when the undercarriage is locked
up; bulbs are usually duplicated to avoid the possibility of false indications as a result
of bulb failures.
Note: Restrictor valves are normally fitted to limit the speed of lowering of the main
undercarriage units, which are influenced in this direction by gravity. The nose
undercarriage often lowers against the slipstream and does not need the protection
of a restrictor valve.
AQUAPLANING
The term given to a condition where the aircraft’s tyres are riding on a liquid film and
are not indirect contact with the runway surface is aquaplaning. The resulting effects
are: Wheel skids, which damage or burst the affected Tyre(s), due to the brakes
locking the wheel(s).
Increased landing roll, due to the loss of braking efficiency Loss of directional control.
Dynamic aquaplaning occurs when standing water on a wet runway is greater than
the tread depth of the type.
TERMINOLOGIES
Crown
This area has the tyre tread and is designed to withstand the wear of normal
operation.
Shoulder
This is a change in profile thickness from the crown and is not designed to take
wear.
Sidewall
This is the thinnest and, therefore, weakest section of a tyre and is designed to flex
when loads are applied.
Bead
This is designed to fit against the rim of the wheel, known as the bead seat.
Not seen so frequently now, but still termed the all weather pattern, is the Diamond
tread pattern.
The tube is inflated through an inflation valve, in which the stem is attached to the
rubber base by direct vulcanization, and the rubber is vulcanized to the tube, renewal
of the inflation valve is not permitted.
TUBELESS TYRES
These tyres are similar in construction to that of a conventional cover for use with a
tube, but an extra rubber lining is vulcanized to the inner surface and the underside
of tyre. This lining, which retains the air pressure, forms an airtight seal on the wheel
rim.
The inflation valve is of the usual type, but is fitted with a rubber gasket and situated
in the wheel rim. The advantage of tubeless tyres over conventional tyres include
the following:
a) The air pressure in the tyre is maintained over longer periods because the
lining is unstretched.
b) Penetration by a nail or similar sharp object will not cause rapid loss of
pressure because the unstretched lining clings to the objects and prevents
loss of air.
c) The tyre is more resistant to impact blows and rough treatment because of
the increased thickness of the casing, and the lining distributes the stresses
and prevents them from causing local damage.
d) Lack of an inner tube means an overall saving of approximately 7.5% weight.
e) Inflation valve damage by creep is eliminated.
TYRE PRESSURES
The difference in landing speeds, loading, landing surfaces and landing gear
construction of aircraft make it necessary to provide a wide range of tyre sizes, types
of tyre construction and inflation pressures.
There are four main categories of tyre pressures, which are as follows:
a) Low pressure. Designed to operate at a pressure of 25lb. to 35lb. per sq. in,
used on grass surfaces.
b) Medium Pressure. Operates at a pressure of 35 lb to 70 lb. per sq. in, (2.42-
4.83 bar) and is used on grass surfaces or an medium firm surfaces without a
consolidated base.
c) High Pressure. Operates at a pressure of 70 lb. to 90 lb. per sq. in, (4.83-
6.21 bar) and is suitable for concrete runways.
d) Extra High Pressure. Operates at pressures of over 90 lb. per sq. in (some
tyres of this type are inflated to 350 lb. per sq. in), the tyre is suitable for
concrete runways.
TYRE MARKINGS
The letters ECTA or the symbol are used to indicate a tyre that has extra carbon
added to the rubber compound to make it electrically conducting to provide earthing
(grounding) between the aircraft and ground.
Bg
WHAT ALL INFORMATION IS PRESENT ON THE SIDE OF THE TYRE
The size of a tyre is marked on its sidewall and includes the following information:-
a) The outside diameter in inches
b) The inside diameter in inches
c) The width of the tyre in inches.
Type of tyre
In this case, the tyre is tubeless type H.
Ply Rating
In this case, the tyre has the strength equal to 22 cotton plies.
Note: The ply rating number does not indicate the physical number of plies.
Together with the load rating, it indicates the strength and corresponding inflation
pressures. See AEA No. below.
Load Rating
In this case, the tyre has maximum static load of 30 100 lb.
Part No.
This is a number specific to the company who manufactured the tyre.
Speed rating
In this case, 245 mph is the maximum groundspeed for which the tyre is tested and
approved.
Tyre Pressure
This indicates the tyre pressure at which the tyre is inflated to prior to fitment tot eh
aircraft.
Green or grey dots painted on the sidewall of the tyre indicate the position of the
“awl” vents. Awl vents prevent pressure being trapped between the plies which
would cause disruption of the tyre carcase if it was exposed to the low pressures
experienced during high altitude flight.
BALANCE MARKER
The lightest point of a tyre cover is indicated by a red spot or triangle painted on the
sidewall of the tyre.
CREEP (SLIPPAGE)
When tyres are first fitted to a wheel they tend to move slightly around the rim. This
phenomenon is called ‘creep’ and at this stage it is considered normal. After the
tyres settle down this movement should cease.
In service, the tyre may tend to continue to creep around the wheel. If this creep is
excessive on a tyre fitted with an inner tube, it will tear out the inflation valve and
cause the tyre to burst.
Creep is less of a problem with tubeless tyres, as long as the tyre bead is
undamaged and any pressure drop is within limits.
Creep is less likely to occur if the tyre air pressure is correctly maintained. To assist
in this, tyre manufactures specify a RATED INFLATION PRESSURE for each tyre.
This figure applies to a cold tyre not under load, that is, a tyre not fitted to an aircraft.
Distortion of the tyre cover when the weight of the aircraft is on it will cause the tyre
pressure to rise by 4%. When checking the tyre pressure of a cold tyre fitted to an
aircraft should mentally add 4% to the rated tyre pressure.
TYRE DAMAGE
Inspecting the aircraft on a pre-flight includes checking the tyres. Pilots qualified on
type are able to check and top tyre pressures if the operator and the authority agree.
Some of the common causes of tyre damage include:
FOD
Foreign object damage (FOD) describes items that should not have been there but
were and have subsequently damaged an aircraft or its equipment. FOD also
describes items that can present a hazard to an aircraft due to their location.
Do not attempt to remove any item stuck in a tyre. It could be lethal. The correct
course of action is to report it, so that the aircraft engineers can reduce the type
pressure and replace the wheel. A screw has greater grip and sealing properties
than a nail due to its thread.
These plugs have a threaded insert of low melting point alloy. If the wheel
temperature reaches a point where the fusible insert melts, the tyre infiation medium
(nitrogen) is released at a controlled rate.
This prevents tyre covers from exploding at high temperatures. The common value
for an air transport aircraft fusible plug is 177C. (Set by Green color)
To indicate that the plug is set at this temperature, it is coloured red. (150°C)
Prolonged braking leads to slow tyre deflation.
This works on the principle that prolonged braking generates excessive heat and the
fusible plugs melt.
The friction pads are made of an inorganic friction material and the plates of ‘heavy’
steel with a specially case hardened surface. It is this surface which causes the
plates to explode if doused with liquid fire extinguish and when they are red hot. In
the unfortunate event of a wheel or brake fire, the best extinguishant to use is dry
powder.
If the brakes become too hot, they will not be able to absorb any further energy and
their ability to retard the aircraft diminishes. This phenomenon is termed Brake
Fade.
If the return spring inside the adjuster assembly ceases to function, or if the unit is
wrongly adjusted, then they could be the cause of a brake not releasing correctly.
This is termed Brake drag.
It is important that the thickness of the brake lining material is carefully monitored.
On multiple disc brake systems, the most popular method of gauging the depth of
brake lining material remaining is by checking the amount that the retraction pin (or
the indicator pin, as it is sometimes called) extends from (or intrudes within) the
spring housing with the brakes.
ANTI SYSTEM
As the pilot’s foot pressure is the controller of the brake pressure, it is possible to
apply a pressure great enough to lock the brake and prevent the wheel from turning,
causing the wheel to skid. This damages the tyre to the point where it can burst (see
tyres), reduce the braking efficiency, and lose directional stability. To overcome this,
anti-skid braking systems are used on modern aircraft.
The basic principle of these systems is the use of the inertia of a flywheel as a
sensor of wheel deceleration. A wheel directly driven by the aircraft wheel is coupled
to the flywheel by a spring. Any changes in aircraft wheel velocity cause a relative
displacement between the flywheel and the driven wheel. This relative displacement
is used as a control signal to operate a valve in the hydraulic braking system to
release the brake pressure.
Semi Modulating
These are first generation electronic systems
Fully Modulating
These are the modern electronic systems fitted to air transport aircraft.
Aircraft fitted with an anti-skid system cannot take off unless it is serviceable.
In the event of a loss of normal pressure supply to the brakes when an anti-skid
device would be operating, provisions must occur for sufficient operation of the
brakes to bring the aeroplane to rest when landing under runway surface conditions
for which the aeroplane is certificated.
To enable the pilot to have full control of the brakes for taxying and manoeuvring, the
anti-skid system is deactivated, either manually or automatically, when the aircraft
has slowed down to below approximately 20 m.p.h., it is assumed then that there is
no further danger of skidding.
The antiskid valves received hydraulic pressure from the normal brake metering
valves
Auto brake selections, deceleration rates, and wheel brake pressure selection
Rate of deceleration Hydraulic pressure applied.
Max, 12 ft/sec 2100 psi
Max, 14.7 ft/sec 2100 psi
RTO Uncontrolled rate of deceleration 3000 psi.
During spray of type I or Type 2 fluid – Engine must be switched OFF, APU may be
running (for lights) with bleed Air OFF (otherwise AC can suck the fluid smell inside
aircraft)
Type 2 fluid is thicker & gives more hold over time (15 min is sprayed 100% cold
spray application.
Types of Ice :
a) Hoar Frost
b) Rime Ice
c) Clear or Glaze ice – cause by large super cooled water droplets most
hazardous.
There are a number of avenues which need exploring and these include detection
and warning systems and the methods used to protect the aircraft, which can be any
or all of the following:
1. Pneumatic . i) Expanding rubber boats – mechanical – De-icing
2. Thermal : i) Electrically heated – Anti-Icing /De-icing cycle timer switch
ii) Oil heated
iii) Air heated – Modern A/c / Anti-icing (Hot air)
3. Liquid – i) Freezing point depressant fluids (FPD)
4. Anti-Icing is the application of continuous heat or fluid
5. De-Icing is the intermittent application of fluid, heat or mechanical effort.
MECHANICAL ‘DE-ICING’
Pneumatic de-icing systems are employed in certain types of piston engine aircraft
and twin turbo propeller aircraft.
De-icer Boots. The de-icer boots, or overshoes, consist of layers of natural rubber
and rubberized fabric between which are disposed flat inflatable tubes closed at the
ends.
The tubes are made of rubberized fabric and are volcanised inside the rubber layers.
In some boats the tubes are so arranged that when the boats are in position on a
wing or tailplane leading edge the tubes run parallel to the span; in others they run
parallel to the chord.
Air supplies and Distribution: The tubes in the boot sections are inflated by air from
the pressure side of an engine-driven vacuum pump, from a high -pressure reservoir
or in the case of some types of turbo-propeller aircraft, from a topping at an engine
compressor stage.
THERMAL “ANTI-ICING” AND DE-ICING
Hot air systems on modern aircraft are generally engine bleed air and are said to be
‘anti-icing’.
Other methods of obtaining the hot air will be described, and depending on
the duration of application and the temperature applied, they may be either
de-icing or anti-icing systems.
In this system, the leading edge sections of wings including leading edge slots but
not leading edge flaps, and tail units are usually provided with a second, inner skit
positioned to form a small gap between it and the inside of the leading edge section.
Heated air is ducted to the wings and tail units and passes into the gap, providing
sufficient heat in the outer skin of the leading edge to melt ice already formed and
prevent further ice formation.
There are two thermal system in use for air intake de/icing; a hot air bleed system
and on electrical resistance heating system, and although the latter is usually chosen
for turbo-propeller engines to provide protection for the propeller, there are some
examples where both systems are used in combination.
Air supplies: there are several methods by which the heated air can be supplied
and these include bleeding of air from a turbine engine compressor, heating of ram
air by passing it through a heat exchanger located in an engine exhaust gas system,
and combustion heating of ram air.
The heat exchanger method of supplying warm air is employed generally in aircraft
powered by turbo-propeller engines.
The power supply required for heating is normally three-phase alternating current.
The arrangement adopted in a widely used turbo-propeller engine.
Both anti-icing and de-icing techniques are employed by using continuously heated
and intermittently heated elements respectively.
The power supply is fed directly to the continuously heated elements, and via a
cyclic time switch unit to the intermittently heated elements and to the propeller blade
elements.
The cyclic time switch units control the application of current in selected time
sequences compatible with prevailing outside air temperature conditions and severity
of icing.
FLUID SYSTEMS
This system prevents the formation of ice on surfaces by pumping de-icing fluid to
panels in the leading edge of the aerofoil, and allowing the fluid to be carried over
the surface by air movement.
The fluid is supplied from the storage tank to the pump through an integral filter.
The pump has a single inlet and a number of delivery outlets to feed the distributors
on the area fail leading edges.
To protect the pump and the system from damage due to pipe blockage etc, the
pump incorporates a safety device which relieves abnormal pressure by reducing the
flow. There are two types of distributor for use with the system, i.e. strip
and panel.
WINDSCREN PROTECTION
Windscreen protection is provided by fluid sprays, electrical heating.
Fluid De-icing system: the method employed in this system is to spray the
windscreen panel with a methyl-alcohol based fluid.
The principle components of the system are a fluid storage tank, a pump which may
be a hand operated or electrically operated type, supply pipe lines and spray tube
unit.
Ice formation on a propeller blade produces distortion to the aerofoil section, causing
a loss in efficiency, possible unbalance and destructive vibration. The build up of ice
must be prevented and there are two systems in use.
Effects of ice
Distorts aerofoil
Causes inbalance
Vibration
Loss of efficiency
Protection by
Anti-icing fluid system
Electrical thermal de-icing system
EMERGENCY EQUIPMENTS
SMOKE DETECTION
Smoke detection systems are employed where it is not possible to keep a bay or
compartment e.g. cargo or electrical equipment, under constant physical surveillance
system of detectors are employed in each compartment bay which can give remote
warnings of smoke, can be tested from the flight deck, and can be re-set when a
warning is received in order to verify it.
Smoke and flame detectors operate according to several different prinicples, for
example:-
a. Light detection
b. Light refraction
c. Ionisation
d. Change in resistance of semiconductor.
Under normal conditions, a beam of light, a known value from the light source,
shines on the sensor cell. As the sensor cell is photoelectric, the light creates an
electrical voltage that is measured and compared against a set value.
When smoke enters the detector chamber, it starts to obscure the light (attenuation).
The subsequent reduction in light falling on the sensor drops the voltage output of
the photoelectriccell. The measuring circuit senses the drop in voltage and triggers
the flight deck warning. This type of detector requires a greater volume of the
previous designs.
Ionisation SMOKE DETECTOR
Electrons have a negative charge while the remaining atoms have a positive charge.
Two separate plates are across the chamber; one has a negative voltage, while the
other a positive voltage supplied from the aircraft’s electrical system.
•
•
When power is applied to these plates, they act as electro – magnets, which attract
theionised particles of the opposite charge.
The electronics within the detection circuit sense the small amount of electrical
current that is created by the electrons and ions moving toward the plates. When
smoke particles enter the ionisation chamber, they disrupt the current being created
by attaching themselves to the ions, which neutralizes their potential. In this
situation, the detection circuit senses the drop in current between the plates. This
triggers the warning.
These Fire wire is mounted as a continuous loop in areas where the outbreak
of fire is possible.
•
Any fault within a fire detection system which may give rise to a false fire
warning must be treated as a real fire.
BUILT-IN TEST-BIT
Modern fire detection systems have built-in test circuits. When electrical power is
applied to the systems, they constantly monitor the loops for integrity of the whole
system. If the test circuit detects a fault, an amber “Fault” light illuminates on the
appropriate fire-warning panel. This alerts the pilot to select the serviceable loop.
BCF is a non-corrosive chemical that forms a blanketing mist when released, which
deprives the fire of oxygen and interferes with the combustion process, preventing
re-ignition.
It is stored as a liquefied gas kept under pressure by nitrogen, which also starts the
expulsion of the liquid from the container when the fire extinguisher is operated.
BCF does not cause cold burns or thermally shock heated metals and has a lesser
toxicity than CO.
It also has the advantage of being directed as a stream from a hand-held fire
extinguisher, allowing the user to fight fires from a safe distance.
BROMOTRIFLUOROMETHANE – CF3BR
BTM-Halon1301 has the same fire knock down properties as Halon1211 but is less
toxic than BCF. It is stored as a liquerfied gas kept under pressure by nitrogen,
which also starts the expulsion of the liquid Halon1301 from the container when the
fire extinguisher is operated.
However, Halon 1301 readily converts to a gas as per CO, and is less direct able
than BCF.
WATER-H20
Water filled hand-held fire extinguishers are carried in the passenger cabins to fight
Class A fires. The water is expelled from the extinguisher by nitrogen gas pressure.
METHYL BROMIDE – MB
Methyl Bromide is stored as a liquefied gas kept under pressure by nitrogen, which
also starts the expulsion of the liquid from the container when the fire extinguisher is
operated.
It is an older agent that is highly toxic and corrosive to aluminium alloys, magnesium
alloys, and zinc.
Methyl Bromide is the most harmful of the agents available and is being phased out
of service as many manufacturers fo not supply or service these units. However, be
aware that some aircraft might still have this agent on board.
SAND
Useful for containing metal fires such as magnesium or titanium where liquids will
make matters worse.
CLASSIFICATION OF FIRES
Class A : Fires that involve solid materials, predominantly of an organic kind such as
paper, cotton, and wood also form glowing embers. The means of extinguishing
these fires is to cool them. The use of water also prevents re-ignition by soaking the
fuel.
Class C: Fires that involve gases or liquefied gases such as butane, propane, and
methane, etc., resulting from spillage or leakage.
The means of extinguishing these fires is to smother them with foam or dry Powder
and use water to cool any leaking container.
Class D: Fires that involve metals such as aluminium. The means of extinguishing
these fires is to smother them with a special dry powder.
•
•
● ELECTRICAL FIRE – CO2 AND BCF (WATER GLYCOL SHOULD NEVER
BE USED)
● ENGINE FIRE – HALON, BCF, METHYL BROMIDE
● CABIN FIRE – WATER GLYCOL, BCF
● BRAKE FIRE – DRY POWDER, FOAM, SAND
(CO2 is never used on brake fire since it causes explosion (thermal shock)
Water has no effect on class D fire explosion (thermal shock) engine fire warning
steady red light and common warning bell.
1. Smoke detectors are fitted in cargo bays, toilets, avionics bay (electrical
equipment bays) where it is not possible to keep physical surveillance.
2. Engine fire extinguisher discharged due to overheat or over pressurization will
be indicated to crew by externally mounted discharge indicator showing red.
3. Engine fire extinguisher discharged due to use by crew will be indicated by
the red pin protruding at the head of the bottle.
4. Cut-in area is delineated buy external marking having right angled corners.
5. Emergency exits are outlined externally by a 2 inch band of contrasting colour.
6. Toilet fire extinguisher is the only automatic fire extinguisher fires when temp
is high in the vicinity.
7. Fire detection system can be tested from the flight deck to verify the warning.
8. Emergency lighting has a min period of 10 min. via vital dc bus bar and
powers light deck lighting, cabin internal and external lighting.
9. Emergency torch is flashing at 4 sec interval (serviceable)
10. Escapes lights are inflated through compressed cylinder of nitrogen. It is
armed only from inside the cabin.
Heater
The next component, the fuel heater, completes the warning of the fuel and the
elimination of ice crystals that may occur. It uses compressor delivery air to warm
the fuel and may be automatic, working in conjunction with the FCOC to maintain a
predetermined fuel temperature, or manual, selected by the flight engineer.
Filter
The fuel filter is in the low pressure side of the system and protects the delicate
control components within the H.P. fuel pump and the fuel control unit (F.C.U.) from
any dirt or contamination.
Flowmeter
The Flowmeter measures the instantaneous fuel flow in Gallons/hour or
Kilogram/hour and may also include an integrator to sum the total amount of fuel
used since the engine was started (Totaliser).
Some engine may use a spur gear type HP pump which is simpler but still supply the
pressure and flow required any excess is recycled back to the inlet side of the pump.
ALSO REMEMBER
GAS TURBINE FUELS
Gas turbine engine aircraft use kerosene fuels. The two main types of gas turbine
fuel in common use in civilian aircraft are shown below, together with their
characteristic properties;-
a) JET A1 (AVTUR) (Aviation turbine fuel). This is a kerosene type fuel with a
nominal SG of 0.8 at 15°C. It has a medium flash point 38.7°C and waxing
point -50°C.
b) JET A is a similar type of fuel, but it has a waxing point of -40°C. This fuel is
normally only available in the U.S.A.
c) JET B (A VTAG) (Aviation turbine gasoline). This is a wide-cut gasoline
kerosene mix type fuel with a nominal S.G. of 0.77 at 15°C. It has a low floash
point -20°C, a wider boiling range than JET AI, and a waxing point of -60°C.
This fuel can be used as an alternative to JET A1 but as can be seen, with its low
flash point is a very flammable fuel and for reasons of safety is not generally used in
civilian aircraft.
Electric power failure in capacitive fuel gauging system will straw full scale deflection
low.
A fuel level drop below a pre-determined level than “low level float” switches will shut
off Jettison valve.
HYDRAULIC SYSTEM
3. A hydraulic fuse?
a. Minimises loss of fluid in the event of a hose failure.
b. Prevents excessive fluid flow rates when jacks become unloaded
c. Limits the rate at which services operate
d. Permits gravity lowering of landing gear.
14. An ACOV?
a. Provides on idle circuit for a constant delivery pump
b. Provides an idle circuit for a variable delivery pump
c. Controls pump output pressure
d. Controls pump output flow
17. Thermal expansion, jack ram displacement and small leaks are allowed for by
the?
a. Reservoir
b. Accumulator
c. Check valves
d. Pressure relief valves
18. Hydraulic pressure pulsations and fluctuations when systems are selected, are
smoothed out by?
a. Accumulator
b. Swash plate pumps
c. ACOV
d. Pressure relief valves
30. If the ACOV in a constant delivery hydraulic system fails in the closed position?
a. Pressure will fall to 0
b. Pressure will remain constant
c. Pressure will increase until the relief valve opens
d. Pressure will increase until the pipes burst or the system is shut down
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11
Ans a c b b d c a c c b c
Ques 12 13 14 15 16 17 18 19 20 21 22
Ans c d a d b b a b c b a
Ques 23 24 25 26 27 28 29 30 31 32 33
Ans a a c b c b c c a a c
HYDRAULICS
2. A pre charge pressure of 1000 bar of gas is shown on the accumulator gauge.
The system is then pressurised to 155 bar, so the accumulator will read:
a. 500 bar
b. 1000 bar
c. 1500 bar
d. 2500 bar
4. A shuttle valve:
a. Is used to replace NRVs
b. Allows two supply sources to operate one unit
c. Allows one source to operate two units
d. Acts as a non-return valve
6. A restrictor valve:
a. Is used to restrict the number of services available after loss of system
pressure
b. Controls the rate of movement of a service
c. Controls the rate of build up of pressure in the system
d. Controls the distance ajack moves
22. Hydraulic pressure of 3000Pa is applied to an actuator, the piston area of which
2 2
is 0.02 m and the same pressure is exerted on actuator whose are is 0.04m .
a. Both have the same force.
b. Both jacks will move at the same speed.
c. The smaller jack will exert a force of 600N and the larger 1200N
d. The smaller jack will exert a force of 60N and the larger 120N
24.In an operating hydraulic actuator the pressure of the fluid will be:
a. Greatest near to the actuator due to the load imposed on the jack
b. Greatest at the opposite end to the actuator due to the load imposed on the
actuator
c. High initially, falling as the actuator completes its travel.
d. The same at all points.
25. The contents of the hydraulic fluid reservoir are checked. They indicate that the
reservoir is at the full level. The system is then pressurized. Will the contents
level:
a. Fall below the “full” mark.
b. Fall to a position marked ‘full aces charged’.
c. Remain at the same level
d. Fries above the “full” mark.
26. A pressure maintaining or priority valve:
a. Enables ground operation of services when the engines are off.
b. Is used to ensure available pressure is directed to essential services
c. Is used to control pressure to services requiring less than system pressure.
d. Is used to increase pressure in the sys
32. The specification of hydraulic fluids (mineral, vegetable or ester based) is:
a. Always distinguishable by taste and smell.
b. Generally distinguishable by colour
c. Generally distinguishable by colour only if they are from the same
manufacturer.
d. Not generally distinguishable by colour.
39. The materials used for moving or sliding seals in hydraulic systems are:
a. Synthetic rubber with vegetable oils
b. Natural rubber with man made oils
c. Natural rubber with mineral oils
d. Butyl rubber with chemically made oils
45. Different diameter actuators supplied with the same pressure at same rate:
a. Exert the same force.
b. Will move at different speeds.
c. Will move at the same speed
d. Exert different forces
2
46.A force of 1500 N is applied to a piston of area 0.002m and generates a force of
2
____ (I) _____N on a piston of area 0.003m . The pressure generated is _____
(2) ____ and, if the smaller piston moves 0.025m, the work done is _____ (3)
______.
a. (1) 56.25J (2) 750000Pa (3) 750000N
b. ( 1) 750000N (2) 2250 P (3) 56.25J
c. (1) 225N (2) 75000Pa (3) 562.5 J
d. ( 1) 1250N (2) 750000Pa (3) 37.5 J
48. The seal materials used with hydraulic fluids to DEF/STAN 91-48 and
SKYDROL 700 specification are respectively
a. Natural rubber and neoprene
b. Neoprene and natural rubber
c. Butyl and neoprene
d. Neoprene and butyl
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12 13
Ans b c d b a b c b c c a b b
Ques 14 15 16 17 18 19 20 21 22 23 24 25 26
Ans d c a c b d a a d a d a b
Ques 27 28 29 30 31 32 33 34 35 36 37 38 39
Ans c d d c d d c c a b b c d
Ques 40 41 42 43 44 45 46 47 48 49 50
Ans a c c d b d d d d d a
AIR CONDITIONING AND PRESSURISATION
7. The rate of change of cabin pressure should be kept to the minimum. Is this
more important:
a. In descent
b. In climb
c. In periods when the dehumidifier is in use
d. In cruise
8. Is a cabin humidifier:
a. On the ground in conditions of low relative humidity
b. At high altitude
c. At low altitude
d. On the ground in high ambient temperatures
10. If the forward oil seal in an axial flow compressor fails, will air be:
a. Contaminated
b. Unaffected
c. ‘b’ is only correct if synthetic oil is used
d. ‘a’ will be correct only if the aircraft is inverted
13. On what principle does the vapour cycle cooling system word on:
a. Liquid into vapour
b. Vapour into liquid
c. Vapour into gas
d. Cold gas into hot gas
14. What is the purpose of the duct relief valve:
a. To protect the undercarriage bay
b. To ensure the compressor pressure is regulated
c. To prevent damage to the ducts
d. To relieve excess pressure to compressor return line
28. With the QFE set on the cabin controller, against an altitude of zero:
a. The fuselage will be pressurized on landing
b. A ground pressurization will automatically take place
c. The cabin will be unpressurised on landing
d. The flight deck will be depressurized
29. In the cruise of 30,000ft the cabin altitude is adjusted from 4,000ft to 6,000ft:
a. Cabin differential will increase
b. Cabin differential will not be affected
c. Cabin differential will decrease
d. Nil
30. An aircraft climbs from sea level to 16,000ft at 1,000ft per min, the cabin
pressurization is set to climb at 500ft per min to a cabin altitude of 8,000ft. The
time taken for the cabin to reach 8,000ft is.
a. The same time as it taken the aircraft to reach 16,000ft
b. Half the time is takes the aircraft to reach 16,000ft
c. Twice the time it takes the aircraft to reach 16,000ft
d. Three times the time it takes the aircraft to reach 16,000ft
31. The aircraft inhibiting switch connected to the A/C landing gear:
a. Allows the aircraft to be pressurized on the ground.
b. Stop pressurizing on the ground and ensure that there is no pressure
differential
c. Ensures that the discharge valve is closed
d. Cancels out the safety valve on the ground
40. During a normal pressurized cruise, the discharge valve position is:
a. At a position pre-set before take off
b. Partially open
c. Open until selected altitude is reached
d. Closed until selected altitude is reached
46. If the cabin pressure increases in level flight does the cabin VSI show:
a. Rate of climb
b. No change unless the aircraft climbs
c. Rate of descent
d. Nil
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Ans b a a b b a a b a a a b a c
Ques 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Ans b b a a b c a c c a a c b c
Ques 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Ans c a b b a c b d a b a b b c
Ques 43 44 45 46 47 48 49 50
Ans d b a c a b a b
PRESSURISATION AND CONDITIONING
8. Cabin altitude?
a. Is actual altitude corrected for sea level pressure
b. The pressure altitude at which the pressure in the cabin would occur in the
ISA
c. The altitude at which pressure inside and outside of the cabin are same
d. The pressure altitude equating to that in the cabin when at cruising altitude.
9. Conditioned air?
a. Is bled from the engines
b. Is air that has had its pressure and temperature adjusted to make it suitable
for use in the cabin
c. Is air that has had its humidity, temperature and pressure adjusted to make it
suitable for us in the cabin
d. Is unsuitable for use in the cabin
11. If the maximum operating altitude is limited by the cabin pressure, the limiting
factor will be?
a. Maximum pressure differential that the system can achieve.
b. Maximum pressure differential that the cabin structure can sustain
c. Maximum pressure differential that the passengers can tolerate
d. Power available from the engines.
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Ans a b a a c b d b c d a c b b b
Ques 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Ans a b b d c c a c c d b b d b b
OXYGEN
3. The maximum altitude without oxygen at which flying efficiency is not seriously
impaired is:
a. 10000 ft
b. 17 500 ft
c. 25 000 ft
d. 30 000 ft
6. In a diluter demand system, selection of emergency on this regulator will result in:
a. Air mix supplied at emergency pressure.
b. 100% oxygen supply as called for by the user.
c. 100% oxygen at positive pressure
d. 100% oxygen continuous flow at positive pressure.
7. If the aircraft suffers a decompression passenger oxygen masks:
a. Are released by the passengers
b. Automatically drop to a half hung (ready position).
c. Are handed out by the cabin staff
d. Must be removed from the life jacket storage
16. If the pressurization system fails and the cabin starts to climb, then at 14000’
oxygen will be available to the passengers by:
a. The stewardess who will hand out masks.
b. The passengers grabbing a mask from the overhead lockers
c. Portable oxygen bottles located in the seat backs
d. Masks automatically ejected to a ½ hung position.
18. In an emergency chemically produced oxygen is supplied for a given period by:
a. Sodium chlorate, iron power, an electrical firing system and a filter.
b. Potassium chlorate, iron powder, an electrical firing system and a filter.
c. Sodium chlorate, iron powder which is chemically activated by air and then
filtered.
d. Sodium chlorate and an electrical firing system
21. With the control knob set to high, a 120 litre portable bottle will provide oxygen
for a period of:
a. 60 mins
b. 30 mins
c. 12 mins
d. 3 mins
22. At what altitude will the diluter-demand oxygen regulator provide 100% pure
oxygen
a. 10,000 ft
b. 14,000 ft
c. 24,000 ft
d. 34,000 ft
24. What is the approximate time of useful conciousness when hypoxia develops at
the specified altitudes.
18,000 ft 30,000 ft
a. 2-3 Min 10-15 sec
b. 10 Min 2 Min
c. 30 Min 90-45 secs
d. 40 Min 5 Min
25. What is the effect on cabin temperature of a rapid de-compression at 30,000 ft.
27. What is the approximate cabin altitude above which you must breath 100%
oxygen if you are to maintain an alveolar partial pressure equal to that at sea
level:
a. 26,000 ft
b. 30,000 ft
c. 34,000 ft
d. 38,000 ft
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Ans c a a a a d b c a c c c c d
Ques 15 16 17 18 19 20 21 22 23 24 25 26 27
Ans a d c a d c b d b c a c c
ELECTRICITY
3. In a three phase star connected AC electrical system, the line current is?
a. The same as the phase current
b. Larger than the phase current
c. 1/ phase current
d. × phase current
7. In a three phase start connected AC electrical system, the phase voltage is?
a. The vector sum of all three phase voltages
b. Equal to the line voltage
c. Less than the line voltage
d. Greater than the line voltage
15. If 10 fully charged lead acid cells are connected in parallel the open circuit
voltage will be approximately?
a. 2.2 volts
b. 2.4 volts
c. 22 volts
d. 24 volts
16. If DC is the primary source of electrical power in a a/c, the AC instruments may
be fed from?
a. A TRU
b. An inverter
c. A rectifier
d. A transducer
c. R/ I
d. V×R
25. What is the difference between (1) a fuse and (2) a circuit breaker.
a. 1 operates on current while 2 operates on power
b. 1 can be reset while 2 cannot
c. 1 operates on power while 2 operates on current
d. 1 cannot be reset but 2 can be
26. Poor bonding will be indicated by?
a. Repeated tripping of circuit breakers
b. Corrosion of skin joints
c. Fuse blowing
d. Static interference on radios
27. What must be the RPM of a four pole AC generator to produce a 400 hz
output?
a. 4000 RPM
b. 6000 RPM
c. 8000 RPM
d. 12000 RPM
28. Fuses will blow when?
a. The circuit has become open circuit
b. Too many loads have been switched off, so excessive current flows in the
remaining loads
c. The loads have become connected in series
d. The circuit has become short circuited
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12
Ans b c a a d d c d d b a c
Ques 13 14 15 16 17 18 19 20 21 22 23 24
Ans d b a b a b a c b d d d
Ques 25 26 27 28 29 30 31 32 33
Ans d d d d a d b d b
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10
Ans a b c d b b c b d b
Ques 11 12 13 14 15 16 17 18 19 20
Ans a b b b d c d a c b
STRUCTURES
2. Trim tabs?
a. Reduce manoeuvring forces
b. Trim the aircraft in normal fight
c. Trim the aircraft in low speed flight
d. Reduce or cancel out control hinge moments
6. Flaperons are?
a. Combined rudder and flaps
b. Combined slats and flaps
c. Combined ailerons and flaps
d. Combined elevators and flaps
15. What is the purpose of the mach trim system in a high speed aircraft?
a. To damp out phugoid motion in yaw
b. To prevent pitch up in shock stall
c. To prevent pitch down in shock stall
d. To prevent dutch roll
16. How do ailerons and roll respond if the control wheel is moved to the left?
a. Left aileron down, left spoiler does not move, right aileron and spoiler up
b. Right aileron and spoiler down, left aileron and spoiler up
c. Left aileron and spoiler down, right aileron and spoiler up
d. Left aileron and spoiler up, right aileron down, right aileron remains retracted
23. The main stresses on the upper and lower skins of a wing in flight are?
a. Compression tension
b. Compression c ompression
c. Tension t ension
d. Tension c ompression
ANSWERS
Ques 1 2 3 4 5 6 7 8 9 10 11 12
Ans b d a c c c c a b b c c
Ques 13 14 15 16 17 18 19 20 21 22 23
Ans c b c d a a d c c a a
7. In a manual flying control system the control inputs to the primary control
surfaces
1. Are reversely
2. Are irreversible
3. Are instinctive for the movement required
4. Are opposite for the movement required
5. Are limited in range by flight deck obstructions
a. 1 and 4 only
b. 2 and 4 only
c. 1 and 3 only
d. 1,3 and 5 only
LANDING GEAR
3. A brake accumulator?
a. Permits use to brakes when engines are stopped
b. Allows for thermal contraction of fluid after shutdown
c. Maintain braking effect in the event of small leaks when parked
4. Thermal bugs?
a. Release brake pressure to prevent overheating of brakes
b. Release excessive tyre pressure to prevent wheel/tyre explosions
c. Heat up the hydraulic fluid to working temperature
d. Active brake cooling fans at some pre-determined temperature
8. Anti-skid system?
a. Increase fluid pressure to the slower level
b. Increase fluid pressure to the faster level
c. Decrease fluid pressure to the slower level
d. Decrease fluid pressure to the faster level
15. Power for the landing gear is usually provided by means of?
a. HP pneumatic system
b. DC electrics
c. AC electrics
d. HP hydraulics
16. The majority of modern transport aircraft use ….. brake units?
a. Drum
b. Multi drum
c. Disc
d. Multi disc
18. Shimmy is often prevented in light aircraft with single nose wheels by?
a. A marstrand tyre
b. Shimmy dampers
c. Power steering
d. Non-castoring nose-wheel
21. The device which ensures that gear doors are open before the gear is raised
to?
a. Micro-switch
b. Squat-switch
c. Sequency valve
d. One way restrictor valve
30. Creep?
a. Is rotational movement of the brake discs when pressure is low
b. Is rotational movement of the tyre around the wheel rim
c. Is caused by excessive tyre pressures
d. Does not happen with tubed tyres
31. Shimmy is?
a. Rapid oscillations of the main wheels about their axles
b. Rapid oscillations of the nose wheel about its vertical axis
c. Slow oscillation of the main wheels about their bogies
d. Slow vertical oscillation of the nose wheels
37. Anti-skid?
a. Prevents wheel locking when taking off
b. Prevents wheel locking when landing
c. Prevents wheel locking when landing and brake application during the
approach to land
d. Operates only in contaminated or wet runway conditions
44. If tyre pressure is 225 psi, its aquaplaning speed will be?
a. 105 kts
b. 115 kts
c. 125 kts
d. 135 kts
46. How is the main undercarriage normally locked in the down position?
a. Hydraulic pressure and mechanical lock
b. Hydraulic pressure
c. Hydraulic pressure and geometric lock
d. A geometric lock and a mechanical lock
48. When the main undercarriage is selected DOWN in flight, it is locked down by?
a. Hydraulic down locks
b. Locking pins and warning flags
c. Sequence valves
d. Spring loaded lock jacks imposing a geometric lock on the side stays or drag
struts
55. A fire of aircraft’s wheel or wheel brake will require which of the following types
of portable hand held fire extinguishers to be used?
a. CO or BCF
2
b. CO 2
c. Foam
d. Dry powder
ANSWERS
5. Creep (slippage):-
a. Is not a problem with tubeless tyres
b. Refers to the movement of the aircraft against the brakes
c. Can rip out the inflation valve and deflate the tyre
d. Can be prevented by painting lines on the wheel and tyre
b. Dry powder
c. Freon
d. Water
9. When inflating a tyre fitted to an aircraft, the tyre pressure reading on the gauge
should be modified by:-
a. 10psi
b. 100/0
c. 4psi
d. 4%
11. The pressure needed to operate the wheel brakes on a large aircraft comes
from:-
a. The aircraft main hydraulic system
b. The pilots brake pedals
c. A self contained power pack
d. The hydraulic reservoir
12. Which of the following statements will produce the shortest landing run:-
i. Crossing the threshold at the correct height and speed
ii. Applying full anti-skid braking as quickly as possible after touchdown
iii. Using maximum pedal pressure but releasing the pressure as the wheels
start to skid
iv. The use of cadence braking
v. Use of minimum braking pressure early in the landing run and maximum
pressure towards the end
vi. Application of reverse thrust as early as possible in the landing run
vii. Deployment of the lift dumpers/speed brakes as early as possible in the
landing run
13. The formula which gives the minimum speed (Vp) at which aquaplaning may
occur is:-
2
where P is kg/cm and Vp is in knots
a.
b. where P is psi and Vp is in mph
c. where P is psi and Vp is in knots
2
d. where P is kg! cm and Vp is in mph
14. An aircraft has a tyre pressure of 225 psi, its minimum aquaplaning speed will
be:-
a. 135 mph
b. 135 knots
c. 145 knots
d. 145 mph
22. At an aircraft taxying speed of 10mph the antiskid braking system is:-
a. Inoperative
b. Operative
c. Operative only on the nosewheel brakes
d. Operative only o the main wheel brakes
23. The tyre pressures are checked after a long taxi to the ramp following landing.
The pressures will have:-
a. Fallen by 15% from their rated value
b. Risen by 15% from their rated value
c. Remained constant
d. Risen by 100/0 of their original value
25. When the landing gear is selected UP the sequence of lights is:-
a. Red, green, out
b. Red, out, green
c. Green, red, out
d. Out, red, green
26. The amount of wear on a reinforced, ribbed tread tyre is indicated by:-
a. The offset wear groove
b. Marker tie bars
c. Concentric wear rings
d. Grey cushion rubber
27. In the event of an approach to land being made with the throttle levers retarded
towards idle and the flaps down and the gear up, the warning given to the pilot
will be a :-
a. Continuous bell
b. Hom
c. Buzzer
d. Stick shaker
28. Lowering the gear using the free fall system will result in the main landing gear
doors:-
a. Closing hydraulically
b. Closing mechanically
c. Remaining open
d. Being jettisoned
29. With RTO (rejected take-off) selected and armed the brakes will be
automatically applied if:-
a. V 1 is not reached after a predetermined distance
b. Vr is not reached after a predetermined distance
c. Reverse thrust is selected at any time
d. One of the thrust levers is returned to idle
30. A green fusible plug is designed to deflate the tyre if a temperature of -------- is
reached.
a. 177°C
b. 277°C
c. 155°C
d. 199°C
ANSWERS
ANTI – ICING
10. With a gas turbine engine, should engine anti-icing be selected “ON”.
a. Whenever the igniters are on.
b. Whenever the IOAT is +10°C or below and the air contains visible moisture
c. Whenever the TOAT is +10°C or below and it is raining.
d. Whenever the ice detector system warning light comes on.
ANSWERS
10. An aircraft is to be de-iced and then enter the line up for departure. Which de-
ice fluid will have the best holdover time at 0°C with precipitation:
a. Type I fluid at 100% cold spray
b. A 50%/50% solution of type II fluid hot spray
c. A 50%/50% solution of type I fluid hot spray
d. Type II fluid at 100% cold spray
ANSWERS
1. A Flight deck indication that a fixed fire extinguisher has been fired is:
a. A green coloured bursting disc
b. A protruding indicator pin at the discharge head
c. Low pressure warning lamp
d. Thermal discharge indicator
2. One type of extinguishing agent you would expect to find in an aircraft installed
engine fire protection system is:
a. Carbon dioxide
b. Argon
c. Helium
d. Freon
3. A wheel brake fire should be fought with a:
a. Water/gas fire extinguisher
b. Dry powder extinguisher
c. Carbon dioxide extinguisher
d. Foam fire extinguisher
On receipt of an engine fire warning on the flight deck the correct procedure should
be:
a. Fight the fire with the flight deck BCF fire extinguisher
b. Pull the fire handle, fire the fire extinguisher, shut down the engine
c. Shut down the affected engine, pull the fire handle, fire the first extinguisher
d. Fire the first extinguisher, pull the fire handle, shut down the engine
9. Fire detection systems:
a. Automatically fire the engine extinguishers
b. Can only use AC electricity
c. Are connected to the Vital bus bar
d. Can be tested from the fight deck
10. A toilet fire extinguisher is activated
a. By high temperature in its vicinity
b. By remote control from the flight deck
c. By a switch at the nearest flight attendant station
d. By a smoke detector
11. Emergency exits:
Can only be opened form the inside
a.
Must have an escape slide fitted to them
b.
Are painted yellow
c.
Must be outlined externally by a 2 inch band of contrasting colour.
d.
12. Regulations governing the fitting, marking and use of safety equipment is
contained in:
a. British Civil Airworthiness Requirements
b. Navigation Regulations
c. Joint Airworthiness Requirements
d. Operations Manual
15. The LED indicator light on the emergency torch is flashing at 4 second
intervals. This indicates:
a. the battery is charging
b. the torch is serviceable
c. the battery needs replacing
d. the filament is broken
17. If the emergency lighting system is powered from the aircraft electrical system,
it takes is power supply from
a. AC essential bus-bar
b. DC essential bus-bar
c. Vital DC bus-bar
d. The inverter
ANSWERS
FUEL STSTEMS
7. The effect of the high pressure compressor outlet pressure exceeding its
maximum value would be:
a. pressure sensor input to fuel control unit (FCU) FCU reduce fuel, reduce
RPM
b. pressure sensor input to fuel control unit (FCU) FCU increase fuel,
increase RPM
c. Pressure sensor input to fuel control unit (FCU), Bleed valve open, bleed
off excess volume of air.
D. pressure sensor input to fuel control unit (FCU), Bleed valve open, bleed
off excess pressure
12. Aircraft flying at FL 420. If the booster pumps feeding the engine cease to
work:
a. The engine would close down immediately
b. The LP pump will draw fuel from the tank, but there may be a possibility of
cavitation due to the low pressure and low boiling point of the fuel
c. The LP pump will draw fuel from the tank, but there may be a possibility of
cavitation due to the low pressure and higher boiling point of the fuel
d. The LP pump will draw fuel from the tank, but there may be a possibility of
cavitation due to the higher pressure and higher boiling point of the fuel.
ANSWERS
FUEL SYSTEM
2. A power failure to a capacitive fuel contents system would cause the gauge to:
a. how full scale deflection high
s
b. f luctuate between high and low readings
c. r emain fixed on the last contents noted before failure
d. how full scale deflection low.
s
3. A fuel booster pump, besides pumping fuel to the engine, can also be utilized to:
a. Jettison and transfer fuel
b. Jettison and heat the fuel
c. Transfer and heat the fuel
d. Transfer and recycle the fuel
4. During fuel jettison, the aircraft is protected against running out of fuel by:
a. High level float switches.
b. Preset jettison quantity switches
c. The crew remaining alert
d. Low level float switches
5. To indicate that a refueling bowser carries JET A1 aviation kerosene:
a. Yellow and black stripes are marked on the refueling hose.
b. JET A 1 would be painted in 30cm high symbols on the side of the container
c. JET A 1 is printed in white on a black background label positioned prominently
on the vehicle.
d. The driver wears a straw yellow water and fuel proof jacket.
6. Adjustments may have to made to an aircraft’s engine fuel system if it has been
refueled with JET B instead of its normal JET A1 fuel, these adjustments are to
cater for:
a. The change in the specific gravity of the fuel
b. The change in the calorific value of the fuel
c. The change in the viscosity of the fuel
d. The lack of HITEC lubricant in the fuel.
7. The differences between AVGAS 100 and AVGAS 100LL are: Colour Anti-
knock value
a. Same Same
b. Same Different
c. Different Same
d. Different Different
ANSWERS
FUEL SYSTEM
1. If a fuel sample appears cloudy or hazy, the most probable cause is:
a. ater contamination
w
b. nti-microbiological additives
a
c. ixing different fuel grades
m
d. il in the fuel.
o
3. The exhaust gases from the A.P.U. go into the refueling zone. The A.P.U. :
a. Must be switched OFF throughout the refueling operation
b. Can be started while refueling is carried out.
c. Must be started before fueling is carried out, and can be run throughout the
refueling operation.
d. Can be started only after the refueling has been terminated.
4. De-fuelled fuel:
a. Can only be used in domestic heating systems
b. Can only be used by aircraft from the same operators fleet
c. Must be put back into storage
d. Cannot be re-used until its quality has been verified
5. The background colour scheme for fueling system pipelines carrying the following
fuel is:
a. Red Black
b. Black Red
c. Red Yellow
d. Yellow Red
6. AVGAS:
a. is coloured red for identification purpose
b. is coloured green if it is a leaded fuel and blue if it is a low fuel.
c. has no artificial colouring and appears either clear or a straw yellow
colour
d. can only be used in piston engines if oil is added to improve its anti-
knock properties.
10. While refueling with passengers on board, when a loading bridge is in use:
a. Two sets of extra steps must be provided, one of which must be at the rear of
the aircraft.
b. The rear left or right door must be manned constantly by a cabin attendant
ready for use as an emergency exit using the inflatable escape slide.
c. Ground servicing must not be carried out.
d. Catering and cleaning must not be carried out.
ANSWERS
FUEL SYSTEM
3. Fuel is heated:
a. t o stop cavitation in the High Pressure Fuel Pump
b. t o maintain a constant viscosity
c. t o prevent water contamination
d. t o stop ice blocking the Low Pressure fuel filter.
6. The advantage of a capacitor type fuel contents gauging system is that the
circuit:
a. responds to changes in specific gravity
b. compensates for high altitude flight
c. responds automatically to extremely low temperatures.
d. compensates for aircraft altitude changes
9. IF a fuel tank with a capacitive quantity system was filled with water instead of
fuel, the gauge would indicate:
a. Full scale low (zero)
b. It would indicate the same as if it were filled with fuel
c. Full scale high (max)
d. It would freeze at the last known indication
ANSWERS