Owner'S & Operator'S Guide: 737Ng Family
Owner'S & Operator'S Guide: 737Ng Family
Owner'S & Operator'S Guide: 737Ng Family
Fleet demographics
The 737NG is operated globally, with
3,225 in service. About one-third of the
fleet is based in North America. The Asia
Pacific and Europe account for 28% and
25% of the aircraft, while the Middle
East operates just 2%. South America
and Africa have small fleets.
Southwest Airlines is the largest
operator, with its 343 aircraft accounting
for more than 10% of the entire 737NG
global fleet. Ryanair is the second largest
operator, with 235 737-800s.
The next two largest fleets are with
Continental Airlines (186) and American
Airlines (119), followed by Gol
Transportes Aereos (90), WestJet (88) and
Alaska Airlines (83). Air China and Delta
Air Lines both have 81 NGs, followed by
China Southern airlines (73) and SAS
(66). China Eastern Airlines and Turkish
Airlines (THY) each have 54. The
popularity of the 737NG is reflected in its
operation by 240 airlines.
While the 737NG is in many ways a
new design of aircraft, it has retained
some levels of commonality with the
Classic, including the flightdeck layout
and the basic airframe design. Differences
include the optional addition of winglets,
advanced avionics, 30% increased fuel
capacity and a new engine.
With the addition of more fuel
AIRCRAFT COMMERCE
Flightdeck
The 737NG flightdeck includes, as
standard, six flat-panel liquid-crystal
display (LCD) screens.
In 2002 Boeing introduced a
demonstrator 737-900 to showcase nine
advanced flightdeck technologies for the
aircraft. These are marketed as an
improved flightdeck experience in both
operation and efficiency, as well as
reducing noise and improving safety.
The 737NG was the first commercial
aircraft to use military Head-up Display
(HUD) technology, although this is still
only available as an option. HUD is a
glass display positioned at eye level that
superimposes an image of the runway
over the actual view out of the window
during take-off and landing. It also shows
critical information such as airspeed,
altitude, attitude and flight path. HUD
aims to reduce flight delays and
cancellations by minimising the effect of
poor visibility; it can allow take-off with
as little as 300 feet of visibility, despite
many regulating bodies requiring a
minimum of 600 feet.
Landing can be improved by adding
an Integrated Approach Navigation (IAN)
system and a Global Positioning Landing
System (GLS). IAN integrates 18
approach procedures into one common
operational approach, while GLS
accurately pinpoints an aircrafts position
and enables airports to remain
operational in adverse weather conditions.
Winglets
The 737NGs standard wings use
advanced technology to ensure an
improvement in fuel efficiency and an
increase in fuel capacity, thereby
increasing the aircrafts range. The wing
area of the 737NG is 25% larger than the
737 Classics, which equates to 30%
more fuel volume, or a standard capacity
of 6,875US Gallons (USG) on all the
series, except the 737-900ER, which also
has two auxiliary tanks.
As mentioned, the economy cruise
speed is Mach 0.78, compared to Mach
0.74 for the 737 Classics.
The 737NGs performance is
ISSUE NO. 70 JUNE/JULY 2010
Engine
options
Maximum
take-off
thrust lbs
MTOW
lbs
MLW
lbs
MZFW
lbs
Max. fuel
capacity
USG
737-600
CFM56-7B18E
CFM56-7B20
CFM56-7B22E
18,400
20,600
22,000
124,000
145,500
145,000
120,500
113,500
120,500
114,000
6,875
6,875
6,875
132
132
132
19,700
20,600
26,100
27,300
133,000
154,500
154,500
171,000
128,000
120,500
737-700BBJ
CFM56-7B20E
CFM56-7B20
CFM56-7B26E
CFM56-7B27E-B3
129,200
134,000
121,700
126,000
737-700C
CFM56-7B24E
23,700
154,500
134,000
126,000
6,875
6,875
6,875
10,707
(9 aux. tanks)
6,875
CFM56-7B24
CFM56-7B26E
24,200
26,100
171,000
171,000
134,000
126,000
6,875
6,875
CFM56-7B24E
23,700
154,500
129,200
121,000
6,875
CFM56-7B26E
26,100
171,000
134,000
126,000
CFM56-7B27/B1
27,300
171,000
737-800BBJ
CFM56-7B24
CFM56-7B24
CFM56-7B27/B1E
CFM56-7B27E-B3
24,200
23,700
28,400
27,300
174,200
155,500
174,200
174,000
144,000
146,300
146,300
136,000
138,300
138,300
737-900ER
CFM56-7B26E
26,100
164,000
149,300
141,300
CFM56-7B26/3
26,300
187,700
CFM56-7B27E/B1F
28,400
187,700
157,300
149,300
27,300
187,700
157,300
149,300
737-700
737-700ER
737-800
737-900ERBBJ3 CFM56-27E-B3
Max. range
2-class with
winglets nm
Typical
cruise
speed (M)
Cargo
volume
-cu.ft.
Overall
length
ft.in.
110
110
110
1,310
3,225
3,225
0.785
0.785
0.785
720
720
720
102'6"
102'6"
102'6"
149
149
149
8+
126
126
126
n/a
0.781
0.785
0.781
0.79
126
126
126
48
76
966
966
966
169
(9 aux. tank)
966
3,750
966
966
3,750
966
110'4"
110'4"
110'4"
110'4"
140
140
10,707
48
(9 aux. tanks)
6,875-10,707
48
(depending on aux. tanks)
76
1,580
3,440
3,440
6,235 (1 class,
& no aux. tanks)
2,725 (1 class)
1,775 (cargo)
3,285 (1-class)
3,285 (1-class)
3,000 (cargo)
3,975 (1 class,
& no aux. tanks)
5,775 (1-class
& 9 aux. tanks)
5,775 (1-class
6,875
6,875
6,875
10,442
(9 aux. tanks)
189
189
189
8+
162
162
162
n/a
3,115
1,995
3,115
5,620 (1 class &
7 aux. tanks)
0.785
0.789
0.789
0.79
7,837
(2 aux. tanks)
7,837
(2 aux. tanks)
215
215
180
1,850
0.79
215
180
3,265
0.78
180
3,265
1,585
8+
n/a
0.79
(2 aux. tanks)
5,495 (1 class &
8 aux tanks)
10,966
(9 aux. tanks)
Typical seating
1
2
class class
76
0.78
0.78
0.78
0.777
110'4"
110'4"
110'4"
110'4"
0.78
183
110'4"
(9 aux. tanks)
0.78
165-966
110'4"
(dependant on aux. tanks)
0.79
1,555
1,555
1,555
256+
129'6"
129'6"
129'6"
129'6"
1,827
138'2"
(no aux. tanks)
1,585
138'2"
(2 aux. tanks)
138'2"
(2 aux. tanks)
208+
138'2"
Engines
All 737NGs are equipped with
CFM56-7B engines. There are six thrust
variants of the -7B series, rated at
between 19,500lbs and 27,300lbs thrust.
The engine offers 180-minute
extended-range twin-engine operations
(ETOPs) and full authority digital
electronic control (FADEC). The CFM567B is a high-bypass, two-shaft engine. It is
based on the CFM56-3, but the -7B
incorporates many of the developments
seen on the CFM56-5A/B series, as well
as improvements of its own (see
Operators & Owners Guide: CFM567B, Aircraft Commerce, June/July 2008,
page 10).
There are also two main upgrade
options available: the Tech Insertion
programme, launched in 2004; and the
CFM56-7B Evolution upgrade,
announced in 2009.
The original CFM56-7B low-pressure
shaft consists of a single-stage 61-inch
diameter fan and a three-stage low
pressure compressor (LPC). The number
of fan blades on the -7B is reduced to 24,
from 44 on the CFM56-3 series. The 7Bs 3-D aero design, increased airflow
and wide-chord fan blades, give it higher
bypass ratios than the -3 and -5A/B
series. The -7Bs bypass ratios vary from
5.1, for the highest rated variant, to 5.5
for the lowest thrust rating. This
compares to a bypass ratio of 4.9-5.0:1
ratio for the -3 series.
The fan is powered by a four-stage
low pressure turbine (LPT).
The high pressure shaft of the original
-7B consists of a nine-stage high-pressure
compressor (HPC). The HPC has been
further developed over the years and the
-7B again benefits from 3-D aero design
techniques to improve efficiency and
aerodynamics. The HPC is powered by
the single-stage high-pressure turbine
(HPT). The -7B uses single crystal HPT
blades.
As an option, the engine is available
with a single (SAC) or double annular
combustor (DAC). Engines with a DAC
are denoted with a /2 suffix, but they
have not been as popular as hoped. The
DAC offers a reduction of as much as
40% of NOx emissions compared to the
AIRCRAFT COMMERCE
Africa
Active Parked
Asia Pacific
Active Parked
737-600
13
737-700
34
201
737-700AEW&C
4
737-700C
737-700ER
12
Middle East
Active Parked
North America
Active Parked
36
3
129
737-700BBJ
737-800
Europe
Active Parked
South America
Active Parked
19
1
69
531
111
11
18
27
20
6
1
85
625
91
23
2
1
737-800BBJ
621
35
9
389
1
737-800P-8A
98
1,866
15
737-900
23
24
52
737-900ER
39
30
71
737-900ERBBJ
Geo sub-total
1
137
908
737-600
The 737-600 is the smallest of the NG
family, and has the same fuselage length
as the earlier -500 and -200 variants. The
-600 has 110 seats in a standard US-style
two-class configuration, and 132 in an
all-economy configuration. This makes it
a direct competitor to the A318 and a
replacement for the 737-500.
Only 69 of these aircraft are operated
by just nine airlines, accounting for just
2% of the fleet. Two large operators are
SAS and WestJet. Others include Malev
and Air Algerie. The oldest aircraft, still
operated by SAS, is over 11 years old.
There are two engine model options
for aircraft up to and including line
number 447. These are the CFM56-7B20
and the -7B22. Aircraft from line number
510 and above are equipped with the
CFM56-7B22.
Over 93% of the former have a
maximum take-off weight (MTOW) of
127,500lbs, and are mainly located in
Europe. The latter have an MTOW range
AIRCRAFT COMMERCE
806
13
69
1,022
1
1
Model Series
Total Total
74
1,046
737-700
The -700 series entered service in
January 1998 with Southwest Airlines. It
is still the largest operator of the 737NG
fleet, and the -700 series in particular,
with a total of 343 aircraft. The 737-700
was designed to replace the -300 and
compete with the A319. The -700 is
powered by two CFM56-7B variants and
the standard fuel capacity remains at
6,875USG.
In total there are 1,144 -700s, with
just over half of them (585) being
operated in North America. Asia Pacific
operates 20% of the fleet, Europe 13%
and South America 10%.
After Southwest Airlines, the largest
operator is WestJet with 64 aircraft,
followed by airTran Airways (52), China
Eastern Airlines (40), Continental Airlines
(36) and Gol Transportes Aereos (29).
There are five models within the
series: the standard -700, the -700C
convertible version, the executive Boeing
Business Jet (BBJ), the AEW&C, and the
long range -700ER.
The standard 737-700 typically
carries 126 passengers in a two-class
configuration, or 149 all-economy seats.
Most, 1,022, are the -700 model, with
again over 50% being in North America.
14
219
3,225
1,144
1,886
126
3,225
737-900
737-800
The 737-800 entered service in April
1998 with Hapag-Lloyd of Germany. The
variant was seen as a replacement for the
737-400 (although the -800 has a longer
fuselage), as well as the MD-80/-90 and
727, and a competitor to the A320. It can
carry up to 189 passengers in a one-class
layout and up to 162 in a two-class
configuration.
The -800 has two more fuselage plugs
than the -700, and an extra pair of
overwing exits. Additional differences
include an increased engine thrust of up
to 27,300lbs, with the -7B27, and a
resized main landing gear and structure.
The 737NG winglets have been
available as a retrofit to the -800 since
May 2001. They improve fuel efficiency
by up to 7%, and increase the range of
the aircraft to 3,115nm when in a twoclass configuration.
The 737-800s size has seen it become
the most popular and the best-selling
variant of the 737NG family, with 1,886
737-800s operating globally. Asia Pacific
and Europe each operate 33% of the
AIRCRAFT COMMERCE
Orders
There are currently 2,047 737NGs
due for delivery from April 2010. This
figure consists of 495 -700s, 1,363 -800s
and 189 -900s/-900ERs.
While North America currently has
the largest NG fleet, the Asia Pacific has
orders for 535 aircraft, 26 units more
than North American operators have on
order.
This coincides with a large growth in
the regional market place for Asian
operators, backed up by the increase in,
and growth of, low-cost carriers (LCCs).
Lion Airlines of Indonesia, for example,
has ordered 148 more aircraft to add to
its current 36, and Virgin Blue is adding
60.
Of the 495 -700s on order, 473 are
for the -700 aircraft, 18 are BBJs, and
four are military convertible -700s. The
largest customer is currently Southwest,
with 87 aircraft due to be delivered by
2017.
Of the 1,363 737-800 aircraft on
order, 1,359 are standard -800 models.
Most of those that have been ordered are
destined for Europe and the Asia Pacific.
The largest orders are with Ryanair
(104), Virgin Blue Airlines (60), and Air
Berlin (51), which also operates 20 737700s.
Of the 189 737-900s that are on
order, 185 of them are -900ERs. There
are 152 destined for the Asia Pacific and
22 going to Europe, while the remainder
are going to Africa and North America.
The biggest order is from Lion Airlines,
which has ordered a total of 148
-900ERs.
As well as by airlines, large orders
have also been placed by lessors, and
many still have a number of aircraft
outstanding. Aviation Capital Group has
orders for 63, DAE Capital has a backlog
of 70, while GECAS is awaiting 66
aircraft.
Developments
There have also been several additions
to the 737NGs design during its
operation. As mentioned there have been
improvements to the flightdeck with
many avionic additions as well as the
addition blended winglets.
Boeing is considering emerging
ISSUE NO. 70 JUNE/JULY 2010
Flight profiles
Aircraft performance has been
analysed both inbound and outbound for
each route in order to illustrate the effects
of wind speed, and its direction, on the
distance flown. The resulting distance is
referred to as the equivalent still air
distance (ESAD) or nautical air miles
(NAM).
Average weather for the month of
Route analysis
Five routes of varying lengths were
analysed with tracked distances of 2121,483nm. The routes were chosen as
examples of flights that Delta Airlines is
currently operating out of its Atlanta
hub. All five routes are in the same
general direction to avoid the effect of
wind distorting the comparison of
different variants over different mission
lengths.
The first route is Atlanta, GA (ATL)
to Columbus/ Starkville/West Point,
known as the Gold Triangle Regional
(GTR) airport, MS. For this route there
was a headwind, causing the tracked
distance of 212nm increase to a longer
ESAD of 228nm.
The second route is ATL to
Springfield, MO (SGF). Again there are
headwinds, which have the effect of
increasing the tracked distance of 543nm
by at least 35nm to an ESAD of 578nm.
The third route is ATL to Omaha, NE
(OMA). There is a strong headwind of
32-36kts, which means that the ESAD
has an average increase of approximately
55nm over the tracked distance to
810nm.
The fourth route is ATL to Denver,
CO (DEN). Again, this route has a strong
headwind, the consequence of which is
that the ESAD is 127nm longer at
AIRCRAFT COMMERCE
Aircraft
Engine
variant
type
Seats
Payload
MTOW
Actual
Block
Wind
ESAD
Track
Max Fuel
Trip
Fuel per
Fuel per
lbs
lbs
TOW
time
kt
nm
Dist
capacity
fuel burn
seat
seat-mile
lbs
min
(nm)
(lbs)
(USG)
(USG)
(USG)
ATL-GTR
ATL-GTR
ATL-GTR
ATL-GTR
B737-600
B737-700
B737-800
B737-900ER
CFM56-7B22
CFM56-7B22
CFM56-7B26
CFM56-7B2 6
110
126
162
180
22,000
25,200
32,400
36,000
143,500
154,500
174,200
187,600
112,576
118,167
132,649
139,540
59
58
62
59
M34
M34
M29
M34
228
226
227
225
212
212
212
212
48,900
39,600
40,000
52,600
535
539
561
586
4.860
4.274
3.462
3.253
0.021
0.019
0.015
0.014
ATL-SGF
ATL-SGF
ATL-SGF
ATL-SGF
B737-600
B737-700
B737-800
B737-900ER
CFM56-7B22
CFM56-7B22
CFM56-7B26
CFM56-7B26
110
126
162
180
22,000
25,200
32,400
36,000
143,500
154,500
174,200
187,600
117,730
123,282
137,962
145,065
102
102
114
102
M33
M33
M29
M33
578
578
582
578
543
543
543
543
48,900
39,600
40,000
52,600
1,218
1,225
1,273
1,322
11.073
9.720
7.859
7.347
0.019
0.017
0.014
0.013
ATL-OMA
ATL-OMA
B737-600
B737-700
CFM56-7B22
CFM56-7B22
110
126
22,000
25,200
143,500
154,500
120,569
126,100
131
132
M36
M36
809
810
752
752
48,900
39,600
1,671
1,679
15.187
13.326
0.019
0.016
ATL-OMA
ATL-OMA
B737-800
CFM56-7B26
B737-900ER CFM56-7B26
162
180
32,400
36,000
174,200
187,600
140,951
148,183
151
133
M32
M36
815
809
752
752
40,000
52,600
1,751
1,813
10.808
10.074
0.013
0.012
ATL-DEN
ATL-DEN
ATL-DEN
ATL-DEN
B737-600
B737-700
B737-800
B737-900ER
CFM56-7B22
CFM56-7B22
CFM56-7B26
CFM56-7B26
110
126
162
180
22,000
25,200
32,400
36,000
143,500
154,500
174,200
187,600
125,228
130,924
145,952
153,147
180
180
209
180
M34
M34
M29
M34
1207
1209
1210
1210
1,126
1,126
1,126
1,126
48,900
39,600
40,000
52,600
2,466
2,476
2,586
2,663
22.419
19.648
15.964
14.792
0.019
0.016
0.013
0.012
ATL-SLC
B737-600
CFM56-7B22
110
22,000
143,500
130,190
232
M38
1611 1,483
48,900
3,255
29.593
0.018
ATL-SLC
ATL-SLC
ATL-SLC
B737-700
CFM56-7B22
B737-800
CFM56-7B26
B737-900ER CFM56-7B26
126
162
180
25,200
32,400
36,000
154,500
174,200
187,600
135,824
151,242
158,460
232
269
232
M38
M33
M38
1610 1,483
1615 1,483
1611 1,483
39,600
40,000
52,600
3,270
3,429
3,516
25.951
21.168
19.531
0.016
0.013
0.012
Source: Jeppesen
1,210nm.
The fifth route is ATL to Salt Lake
City, UT (SLC). This is a route that
experiences the strongest headwind of up
to 38kts, which therefore results in an
increase in ESAD of at least 127nm to
1,611nm.
The block times and winds for the
737-600, 700 and -900ER are all very
similar on each route, with only two
minutes maximum between block times
(see table, this page). The -800 on shorter
routes shows a small difference compared
to other variants in terms of absolute fuel
burn, but on longer routes the difference
in fuel burn per seat between variants
actually widens. For the -800, the winds
are weaker, although they are still
headwinds, thereby making the ESAD
longer than the tracked distance and, in
most cases, making it the largest ESAD
when comparing variants within a certain
route.
AIRCRAFT COMMERCE
737NG maintenance
analysis & budget
The 737NG has a flexible maintenance programme
that allows airlines to package tasks into checks that
suits their operation. This results in lean maintenance
requirements and low reserves for base maintenance.
737NG in operation
There are four main 737NG variants:
the -600, -700, -800 and -900. The -700
and -800 dominate the eet with 1,014
and 1,864 aircraft respectively. The
737NG has more than 240 operators in
all continents, with eet sizes varying
from just a few aircraft to more than
200-300 aircraft in some cases.
There are just 63 737-600s in
operation, with the biggest operators
being SAS and Westjet. Average annual
utilisations are 2,600 ight hours (FH)
and 1,900 ight cycles (FC), with an
average FC time of 1.4FH.
The 737-700 eet is the second
largest, with 1,014 aircraft. Major
operators include Aeromexico, Air Berlin,
AirTran, Alaska Airlines, China Eastern,
China Southern, Continental Airlines,
GOL, Southwest, Virgin Blue and
Westjet. Southwests eet of 343 -700s is
far the largest eet. Westjet operates 64
737-700s.
Annual rates of utilisation average
AIRCRAFT COMMERCE
MPD
The 737NGs MPD simply lists all
maintenance inspections and, unlike the
737-300/-400/-500s MPD, does not
group them into pre-dened airframe
checks such as A, C or D checks.
The tasks in the 737NG MPD fall
into three categories: systems and
powerplant tasks, as specied in section 1
of the MPD; the structural maintenance
programme, as specied in section 2; and
the airworthiness limitation limits
(AWLs) and certication maintenance
requirements (CMRs), explains
Firtinoglu.
The tasks have intervals specied in
one or two of three parameters: ight
hours (FH), ight cycles (FC) and
Check planning
A checks
Most operators still use a system of
A checks with intervals every 400700FH, and C or base checks with
intervals every 4,000-6,000FH and 18 or
24 months. Tasks with the shortest
intervals will be included in line checks,
while those tasks with odd intervals that
do not coincide with any of the line
checks or A or base check intervals will
be grouped by operators into checks as
they come due.
The MPD line check tasks are
specied in the usual pre-ight, daily,
overnight and weekly intervals. Most of
these tasks come from the ight
operations manual, and a few from the
MPD. Aircraft operating at 3,300FH per
year are accumulating 65FH per week, so
weekly checks therefore provide an
opportunity to include tasks that have
intervals between 60FH and the
operators chosen interval for A checks.
Rae explains that the KLM line
maintenance programme consists of a
pre-ight check prior to every ight, for a
maximum ground time of four hours; an
overnight check, which is valid for 28
hours; and a daily check every day, which
is valid for 48 hours. Some drop-out
tasks get planned into overnight and daily
checks, says Rae.
The logical choice for A checks is the
interval which divides exactly into the
majority of task intervals. That is, 500FH
should be used if most tasks are a
ISSUE NO. 70 JUNE/JULY 2010
FH
FC
FC/
time
Time
TOTAL
1C
2C
3C
4C
5C
6C
7C
8C
157
45
3
23
8
1
28
156
6
79
73
30
20
58
12
18
7
20
11
372
91
100
107
59
36
Total
235
Task group
4
1
5
7
46
364
126
772
C1
C2
C3
C4
C5
C6
C7
C8
1c
2C
3C
4C
5C
6C
8C
372
372
91
372
372
91
372
372
91
100
372
372
91
TOTAL
372
Task group
100
107
36
7
463
472
107
59
570
431
599
372
577
Base checks
Tasks with intervals higher than
6,000FH and up to 11,500FH can either
be performed early and grouped together
at every 6,000FH interval and included in
the base checks, or as they come due and
AIRCRAFT COMMERCE
A check inputs
Operators can choose a variety of
intervals for A checks, and package tasks
in many different ways when using the
same interval.
With a 600FH interval to analyse the
737NGs maintenance costs, the tasks
between the weekly and A checks are
taken into consideration. Some operators
bring certain tasks, such as lubricating
items like the landing gear and ap and
slat mechanisms, forward into weekly
checks, while others use intermediate
checks. Turkish Airlines has recently
changed to an equalised system of checks
at 150FH intervals in order to address
this issue.
A check tasks include those in the
weekly check, some functionality tests,
checks on emergency and safety
equipment, control surfaces and
mechanisms, and some non-destructive
tests on a few parts.
Using a 600FH interval for the A
check and 6,000FH interval for the C or
base check means the ninth or tenth A
check will be combined with the base
check, depending on check interval
utilisation. These two interval
parameters, and the absence of an
intermediate check have been used to
illustrate MH consumed in A and base
checks.
The workscope of A checks will start
with routine inspections. The A6 and
A10 checks at 3,600FH and 6,000FH
have a larger group of routine tasks, and
so will be the larger checks. There will be
40-75MH used for the eight lighter
checks, while the A6 check will use
145MH, and the A10 check will use
205MH.
Airworthiness directives (ADs),
AIRCRAFT COMMERCE
Using the 6,000FH, 3000FC and 24month interval for this analysis, tasks can
be grouped into block checks, so that the
peaks in the number of tasks would occur
with the C4, C6 and C8 checks. There is
no particular cycle of checks, and the
number of tasks for each check varies.
The C12 would have the largest number,
with 1C, 2C, 3C, 4C and 6C all coming
due at the same time, totalling 706 tasks.
These tasks form the routine
inspections for each check. Despite the
number of tasks being grouped as
described, operators will not use the full
interval of each check. Actual rates of
interval utilisation are typically 85%. At
this rate, base checks would be performed
every 20 months and 5,600FH and
2,900FC. With this actual interval,
maintenance planners would group tasks
into checks so that the aircraft was free of
all major tasks for up to 24 months.
Moreover, the rst aircraft delivered in
the late 1990s would have had base check
intervals close to 5,000FH and 18
months, so the number of tasks would
not be as described.
The C5 check would therefore come
due at eight-and-a-half to nine years,
while the C6 check would come due after
10-and-a-half to 11 years. The large
group of structural tasks with a 10-year
interval would therefore have to be
performed at the C5 check, making it a
heavy check. The C7 check would come
due at 12 years. The C6 check would
then have a relatively low number of
tasks, while the C7 check would have a
large number of tasks, including the 30 or
so tasks that have an interval of 12 years,
making it a heavy check.
The inputs for routine tasks and
inspections for these rst seven checks
would be 1,000MH for the C1 check,
rising steadily for each check up to the
C5 check to 2,500MH. The C6 would be
smaller, using 2,000MH, and the C7
would be larger again using 2,400MH.
The total labour input for these checks
over a period of 12 years and interval of
67,000FH is 13,000MH.
The extra items included in the base
checks are: AD inspections and SB
modications; non-routine rectications;
component changes; interior cleaning;
ISSUE NO. 70 JUNE/JULY 2010
Components
The 737NG has 2,500-3,000 rotable
components, depending on conguration
and aircraft specication. These include
landing gear and safety equipment. About
6%, 150-200, of these are maintained on
a hard-time basis.
The remaining 2,300-2,800 rotables
are maintained either on-condition (550700) or are condition-monitored (1,8002,100).
Rotable components can be subdivided into heavy components and all
other rotables.
Heavy components
There are four main heavy
components of wheels and brakes, thrust
reversers, the APU, and the landing gear.
Wheels and brakes require the
maintenance of tyres, wheel rims and
brake units. Tyre wear and brake pad
thickness are checked during transit and
pre-ight checks.
Wheels are removed when tyres
become worn. In the case of nosewheels,
this is typically up to 200FC, and at a
slightly shorter interval for mainwheel
tyres.
At this stage tyres are remoulded.
Mainwheel tyres can be remoulded ve or
six times, while nosewheel tyres can be
remoulded 10 or 12 times. It costs $200ISSUE NO. 70 JUNE/JULY 2010
Rotables
Engine maintenance
The CFM56-7B family has six main
variants, each with a thrust rating
ranging from 19,500lbs to 27,300lbs (see
CFM56-7B Owners & Operators
Guide, Aircraft Commerce, June/July
2008, page 9). The engine variants for
each variant of the 737NG are
summarised (see 737NG family &
CFM56-7B specifications, fleet &
developments, page 4).
Several modications have been made
ISSUE NO. 70 JUNE/JULY 2010
AIRCRAFT COMMERCE
-7B20/22
These lower-rated engines are capable
of rst removal intervals of up to the rst
LLP limit, which is 20,000EFC for parts
in the two HP modules. The EGT margin
of these engines is in fact high enough for
them to remain on-wing for up to
25,000EFC. These long intervals are
equal to 39,000-49,000 engine ight
hours (EFH) at the average FC time being
used in this analysis. The engines are
therefore likely to also experience
mechanical deterioration and reliability
problems at these long intervals.
Some older LLPs in the HP modules
have lives lower than 20,000EFC, and so
will limit the rst removal intervals of
these older engines. In most cases, these
lower-rated engines should be able to
achieve rst on-wing intervals of up to
20,000EFC.
At this stage, shop-visit workscopes
are considered. A heavy workscope will
clearly be required on the HP modules,
resulting in a restored EGT margin of 75100 degrees. This will allow a second onwing interval of 20,000EFC, subject to
restrictions placed by mechanical
deterioration. This will only be possible,
-7B24
The -7B24s lower initial EGT margin
of 100 degrees will allow a rst on-wing
interval of 18,000EFC, when operating in
temperate climates, equal to 34,000EFH,
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-7B26
The -7B26s EGT margin of 80
degrees allows a rst removal interval of
14,000EFC. The restored EGT margin
after the rst shop visit of 45 degrees
would only allow a second interval of
9,000EFC. It should be appreciated that
this variant has HPT LLPs at 17,600EFC,
which would limit the second interval.
A level 2 workscope on the HP
modules is therefore required at the rst
shop visit.
The fan/LPC LLPs will have
remaining lives of 11,000EFC, the
maximum possible second removal
interval. The second removal is only
likely to be 9,000EFC, however, before
EGT margin is eroded. Fan/LPC LLPs
will only have 5,000-7,000EFC
remaining. The workscope at the second
shop visit will require full overhauls of
the two LP modules to allow LLP
replacement. The HP modules will only
need a level 1 workscope, since they will
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-7B27
Like the -7B26 non-Tech56 variant,
the -7B27s initial EGT margin allows a
rst removal interval of only 11,000EFC.
The total of the rst and second
removal intervals will be limited to
17,600EFC. Restored EGT margin, of
39-44 degrees, will allow second and
Workscope inputs
There are four types of workscope for
which inputs and costs have to be
considered. Shop-visit costs comprise
routine and non-routine labour, parts and
materials, and sub-contract repairs.
The cost of each item will depend on
the percentage of parts that can be
repaired, or scrapped and replaced with
new parts. A higher rate of repair will use
relatively large amounts of labour and
have a high sub-contract repair cost. A
high rate of replacement and a low rate
of repair will utilise less labour but cost
more in materials and parts.
Shop-visit costs also depend on the
shops in-house capability for hi-tech
repairs. A small capability will see smaller
labour and materials inputs, but greater
expense for sub-contract repairs.
A core restoration will use up to
2,500MH for all labour inputs, up to
1,500,000 for materials, and $250,000400,000 for sub-contract repairs. The
higher material cost will cover 100%
HPT blade and nozzle guide vane (NGV)
replacement. Using a generic labour rate
NDT specialise in
Borescope inspections
3$57TXDOLHG
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CFM 56
&HUWLFDWHRIUHOHDVH
ZRUOGZLGHVHUYLFHV
Non destructive testing worldwide services
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AIRCRAFT COMMERCE
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for leading airlines and
MROs worldwide
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on Elevators and Rudders
by d.
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6
Removal
interval
EFC
Shop
visit
LLP
workscope replacement
Shop
visit
cost-$
LLP
cost-$
Reserve
$/EFC
Unsched
visits
$/EFH
QEC
$/EFH
Total
$/EFH
-7B20/22
1st
2nd
20,000
20,000
Full overhaul
Full overhaul
All parts
All parts
2,200,000
2,600,000
2,110,000
2,110,000
216
236
31
31
10
10
152
162
-7B24
1st
18,000
2,250,000
1,684,000
241
31
10
165
2nd
12,000
fan/LPC
2,050,000
424,000
257
31
10
173
3rd
8,000
Level 2 core
& LPT
level 1 core &
level 2 fan/LPC
Level 2 core
& LPT
2,350,000
1,684,000
375
31
10
233
All parts
Core & LPT
2,200,000
2,350,000
2,110,000
1,684,000
216
269
31
31
10
10
152
179
Full set
2,250,000
2,110,000
291
31
10
190
14,000
Level 2 core
Core
8,800
level 1 core,
Fan, LPC &
level 2 fan, LPC & LPT
LPT
8,800
level 2 core
Core
1,800,000
2,200,000
1,090,000
1,018,000
251
315
31
31
10
10
170
202
2,000,000
1,090,000
352
31
10
221
-7B24-Tech56
1st
2nd
20,000
15,000
3rd
15,000
-7B26
1st
2nd
3rd
-7B26 Tech56
1st
2nd
Full overhaul
Level 2 core
& LPT
level 2 core
& fan/LPC
1,800,000
2,200,000
1,090,000
1,018,000
237
297
31
31
10
10
162
193
3rd
16,000
Level 2 core
Core
9,000
Level 1 core,
Fan, LPC&
level 2 fan, LPC & LPT
LPT
11,000
Level 2 core
Core
2,000,000
1,090,000
301
31
10
195
-7B27
1st
2nd
10,000
7,600
1,600,000
2,350,000
0
1,684,000
303
406
31
31
10
10
196
249
Fan/LPC
1,850,000
424,000
359
31
10
225
1,700,000
2,350,000
0
1,684,000
267
374
31
31
10
10
178
233
Fan/LPC
1,950,000
424,000
295
31
10
192
3rd
-7B27 Tech56
1st
2nd
3rd
7,400
Level 1 core
Level 2 core
& LPT
Level 1 core,
level 2 fan/LPC
12,000
8,000
Level 1 core
Level 2 core
& LPT
10,000
Level 1 core
& level 2 fan/LPC
Engine reserves
The removal intervals, shop visit
workscopes, LLP replacement, shop visit
costs and reserves in $ per EFC are
ISSUE NO. 70 JUNE/JULY 2010
Cycle
cost-$
Cycle
interval
350,000
165,000
25 million
85,000
Annual
5,100FH
39,000FH
16,800
Heavy components
Cost per
FC-$
Cost per
FH-$
110
32
65-70
5
28
254
130
235-255
605-630
Engine maintenance:
CFM56-7B20/22:
CFM56-7B24:
CFM56-7B24 Tech56:
CFM56-7B26:
CFM56-7B26 Tech56:
CFM56-7B27:
CFM56-7B27 Tech56:
304-324
330-466
304-380
340-442
324-390
392-498
356-466
909-1,128
Annual utilisation:
3,300FH
1,700FC
FH:FC ratio of 1.95:1
Summary
The 737NGs total maintenance costs
are $909-1,128 per FH, depending on
aircraft variant and engine model, for
aircraft in their rst cycle of main base
checks, up to their sixth or seventh base
checks at an age of 12-14 years, and for
aircraft with engines that are up to their
third removal and shop visit, which can
be as long as 50,000FC and 100,000FH,
equal to more than 25 years operation.
The varying total cost per FH is due
mainly to the engine reserves, which
gradually increase from the rst to the
third removal. The engines of most
737NGs are within their rst or second
engine removal cycles, so higher engine
reserves apply to few operators.
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ISSUE NO. 70 JUNE/JULY 2010