Pilatus PC-12 Assembly Line: Industrialization, Manufacturing and

Process Improvement
Raúl Diego Guichón Aguilar
Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal

Introduction
OGMA Aerostructures
OGMA is a supplier of integrated solutions
This study is based on a real case, the to OEMs and a first tier supplier, committing
Pilatus PC-12 assembly line. to the Aerostructures market for over 30
As major aircraft original equipment years. As a full service provider OGMA is
manufacturer (OEM), Pilatus Aircraft tends able to deliver Aerostructures assemblies
to focus more on systems integration. As a and sub-assemblies, either from metallic or
result of this approach, manufacturing composite materials, covering a broad
services are subcontracted to tier-one spectrum of Aerostructures family products.
companies, such as OGMA Aerostructures, Approved by EASA (European Aviation
which produces the Pilatus PC-12 green Safety Agency) as POA (Production
aircraft. Organisation Approval), Part 21, Sub-Part
A tier one company is the most important G, its technical competence, quality and
member of a supply chain, supplying performance allow OGMA to deliver on-
components directly to the original OEM time, low risk competitive solutions with a
that set up the chain. Creating a tiered broad portfolio of major players in the global
supply chain is part of supply chain aviation market.
management. Its aim is to link important The Pilatus PC-12 program started at
business functions and processes in the OGMA’s facilities in 1994. Nowadays, the
supply chain into an integrated business PC-12 green aircraft is entirely assembled
model. at Alverca’s facilities.
Tier one companies are generally the
largest or the most technically-capable Pilatus PC-12 Program
companies in the supply chain. They have Over 1200 PC-12s have been delivered
the skills and resources to supply the world-wide as at the beginning of 2014.
critical components that OEMs need and The PC-12 is a pressurized single turbine
they have established processes for powered by a Pratt & Whitney PT6A-67B
managing suppliers in the tiers below. turboprop engine utility aircraft, which
In this case, tier one company provides a operates up to 30,000 feet and 250 knots
manufacturing service for the OEM, leaving as it is takes off from or landing on very
the OEM to concentrate on final assembly, short dirt runways. It has the range to fly six
design and support engineering and passengers up to 1560 NM, or the ability to
marketing. fly one and a half tons of cargo over 400
Tier one companies develop close working nautical miles with IFR reserves. Maximum
and business relationships with OEMs. certificated passenger capacity is nine in
Both organizations recognize the value of the airline configuration, or eight in the
collaboration to improve quality, eliminate optional executive configuration. The
waste, cut costs and reduce lead times. aircraft is unique in its class in that it has
The main objective of this study is to both a forward air stair door for passengers
analyze industrialization and manufacturing and a powered rear cargo door.
processes and applicability of state-of-art Pilatus Aircraft continuously improve its
optimization techniques for those products, and, as part of that effort,
processes. introduced the Next Generation PC-12 at
the end of 2007.

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Parts and assemblies of PC-12 Program Aerostructures
The Pilatus PC-12 structures produced by
OGMA are shown and listed below: Industrialization

Industrialization of aircraft manufacturing

products includes a set of activities of
engineering, logistics, quality, scheduling,
production and process control, focused on
ensuring production according to applicable
regulations. Manufacturing is a process
consisting in converting raw materials,
1-Wings 2-Fuselage components or parts into finished goods
3-Dorsal fairing 4-Vertical Stabilizer
5-Rudder 6-Ailerons that meet customers’ specifications.
7-Flap fairings 8-Ventral fairing
9- Doors 10-Harnesses Industrialization process
11-Flaps
The industrialization process is started
upon Customer PO (purchase order)
Fig. 1 – Pilatus PC-12. Courtesy of OGMA issuance with provision of the applicable
technical data [1].
Pilatus PC-12 Production Line The activities constituting the
The PC-12 assembly line is located inside a industrialization process are:
multi-program plant, where several  Receiving technical data
aerostructures are assembled. The  Analysis of technical data
Production planning and the Plant Layout  “Make or Buy” analysis and
enables to manufacture up to five different decision
aerostructure programs within the same  Tool and jig design and
plant: EH-101 tail assembly, Pilatus PC-12 manufacturing
green aircraft, Dassault Falcon Pylon, ADS  Process certification
C-295 Central Fuselage and Embraer KC-  Defining engineering product
390 Central Fuselage. The PC-12 assembly structure
line is composed by 8 main different stages,
 Defining manufacturing product
where 13 structures are manufactured:
structure
cockpit, floor, rear fuselage, fin (including
 Creation of Items, Bills of Material
rudder), wings (including flaps and
and Production Routings
ailerons), sidewalls (RH and LH), rooftop,
 Intermediate and Final Inspection
fuselage and doors.
 Material procurement
 Realizations of FAI (first article
inspection) product
 Manufacturing Product Handling,
Storage, Packaging and Shipment
 Support or Post-industrialization
1-Cockpit
2-Rear Fuselage phase
3-Sub-assemblies  Industrialization management
4-Doors
5-Wings, aileron
and flaps Configuration management
6-Sidewalls and floor Configuration control of aircraft
7-Cabling
8-Rooftop manufacturing products guarantees that the
9-Fuselage current product configuration is updated
integration
and the applicable technical data are
available at all times throughout the
process. This activity does not apply to
configuration changes of the product itself,
since these are the responsibility of the
project owner.
Configuration control of aircraft
manufacturing products is limited to:
Fig. 2 – Pilatus PC-12 Production Line,  Control of product related technical
FMT Layout. Courtesy of OGMA data changes/revisions

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  Implementation of changes in the Industrial Engineering
support technical data and in the Specific programs of improvement are
productive process required for manufacturing, such as time
 Verification of change and and costs reduction, reduction of process
implementation in product parameters variability and quality
improvement. Consequently, Continuous
Improvements plans are implemented
Aerostructures (PMC) after requests for continuous
Manufacturing improvement (PMP’s). PMC’s are mid/long-
term plans, which resolution and
implementation takes time and additional
1. Process Engineering costs [3].
Once the industrialization process finishes Manufacturing process
by the complaining of the FAI (first article
inspection), the manufacturing process Process analysis
begins. At this stage a set of actions are In order to optimize processes, data
implemented: collection is required. Data is obtained from
 Process improvement, in terms of the Enterprise Resource Planning software,
operations sequencing, timing and quality and production records. Some
methods information can only be obtained by
 Implementation of customer observing (creating records or estimating
modifications, after analysis and parameters from related data) or creating a
engineering product structure recording system.
definition A proposed methodology to optimize and
 Production support actions implement new processes is DMAIC: define
 Process engineering is responsible processes, measure parameters, analyze
for nonconforming product, process obtained data, improve current processes
support during manufacturing, and control it.
process improvement, Tools used by process engineering [4]:
manufacturing products  SIPOC analysis
management, technical  Process Flowchart
documentation, manufacturing  Key parameters indicators and key
modifications implementation, performance objectives
timeframes and methods  Graphical analysis
engineering, production resources  Characterization of variables
training, subcontractors support distribution
and tooling.
Nonconformance analysis
Nonconformance product It is the responsibility of every OGMA’s
During the manufacturing process (support employee to report nonconformity detected
phase), it is required analyzing and solving at any stage of the process, in order to
product nonconformities generated by the analyze and correct it, even when it
manufacturing process, as well as involves products already delivered to
implementing required corrective actions. Customer.
Nonconforming product attributions of The product related functional areas
engineering are: analyzing and solving the (Production, Product Quality, Engineering,
product nonconformity occurred during the Planning, Programming & Control and
manufacturing process (excluding MRB Logistics) shall assess the nonconformity
activities)[2], creating the required and decide on the action to be taken on the
disposition and identifying improvement nonconforming product, involving in the
opportunities, implementing corrective decision, where applicable, the Customer,
activities according to customer’s the manufacturer and the competent
requirements, evaluating nonconformities Aviation Authority.
impact, implementing the required
corrective actions, analyzing the repeated Scratch-damaged Rear Pressure Bulkhead
nonconformities reported in RAC’s and According to the nonconformance product
promoting new improvement opportunities procedures, a nonconformance report
and ensuring the right implementation of delivered to the customer must be followed
corrective/preventive actions after the by substantiation (document that contains
PAC/P release.

3
engineering analysis that supports the cases in the design and development of the
proposed solution). aircraft. A Pilatus PC-12 rear pressure
One of the main causes of RAC openings bulkhead with all stiffening members is
at the rear fuselage is scratch damage considered in this analysis.
produced during manufacturing. In order to The pressure rear bulkhead is connected to
understand how those anomalies affect the the airframe by a doubler that is connected
product life and the structural stability of the simultaneously to a stiffener frame
component a structural analysis is realized. (frame36), rear fuselage and central
This analysis is based on typical skin fuselage skins and stringers. The frame is
repairing procedures. much more rigid than the pressure
bulkhead flange, all tension loading at this
section is supported by the frame. That is
the reason why the selected loading for this
analysis is a pressure load of 5.7 psi, which
is the maximum pressurize differential of
the Pilatus PC-12 NG.
Geometric modelling
A rear pressure bulkhead is considered for
the analysis. The pressure rear bulkhead is
manufactured from a solid formed sheet of
aluminum of a constant thickness. The
flange reinforcements and stiffeners are
formed on the outer surface of the pressure
rear bulkhead by chemical milling.
After getting the geometry of the pressure
Fig. 3.– Example of typical anomalies found rear bulkhead some constraints are
in a Pressure dome, 3 scratches on the considered: symmetry of the component
inner face. could simplify the analysis, working with a
half and using the right boundary
conditions, and a mapped mesh of quad
elements would increase reliability of the
model. Geometry complexity makes this
mesh implementation difficult, manual area-
by-area meshing was implemented in order
to mesh as described. Even though, more
complex areas are meshed using free-quad
elements.
Selected elements
The selected element is Shell-181 for all
component surfaces. SHELL181 is suitable
for analyzing thin to moderately-thick shell
structures. It is a four-node element with six
degrees of freedom at each node:
Fig. 4. – Scratch example. Courtesy of translations in the x, y, and z directions, and
OGMA rotations about the x, y, and z-axes.
SHELL181 is well-suited for linear, large
Static Structural Analysis
rotation, and/or large strain nonlinear
The analysis is focused on finding stress
applications. In the element domain, both
distribution and loading of the rear pressure
full and reduced integration schemes are
and the sensibility of this structure to a
supported. SHELL181 accounts for follower
repairing operation, the skin thickness
(load stiffness) effects of distributed
decrease. This analysis is based on
pressures.
commercial software, ANSYS APDL.
Boundary Conditions and Load
Fuselage experiences a small percentage
All translation degrees of freedom of the
of lift loads, but the dominating load on the
RPB flange are fixed and rotation is free
fuselage is the Inertia load. When the
(supported flange). The load condition is
aircrafts fly over high altitude an internal
the pressure load acting at the entire skin
pressurization is applied to create the sea
(from inner to outer surface).
level atmospheric pressure inside the
fuselage cabin. This internal pressurization
is considered to be one of the critical load

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Linear-static structural analysis
Applied boundary condition is a
conservative approach to real boundary
conditions, because stress at studied areas
(flange and central membrane are not
considered for this analysis) are over-
estimated but in an acceptable range, and
that means a safety factor greater than 1.5
for maximum pressure differential.
At flange, stress is under-estimated
because the selected boundary condition
(supported flange) reduces stress at flange Fig. 6. – Thickness decrease analysis
and increase stress at the rest, comparing mesh, modified area identified in blue at the
to real loading. Even though, it is a good right picture.
boundary condition approach for this
analysis.
At central membrane (the most stressed
area), tension is over-estimated because of
lack of stiffeners and as at the rest of the
central area of the pressure rear bulkhead
stress is sensibly over-estimated because
of boundary conditions.

Fig. 7. – Detail of the defect.

The thickness decrease simulated
generates a stress concentration at the
surrounding area. The stress concentration
generated at the FEM model is greater than
in the real pressure rear bulkhead because
of the smoother contour of the last, even
though stress levels remain in the
Fig. 5– Von Misses Equivalent Stress plot acceptable range and FEM analysis
of outer face. remains conservative.

Thickness decrease sensibility analysis

With the purpose of understanding the
impact of standard scratch repairing
processes on pressure rear bulkheads. The
selected defect is a scratch on the bottom
center side of the pressure rear bulkhead,
the standard repairing process is a
progressive thickness decrease at the
surrounding area. The modified area is
30 , and the modification is of 10% or
25% decrease of the nominal thickness.
The selected mesh has 12846 shell-181 Fig. 8. – Von-Misses stress distribution for
elements. inner face thickness decrease of 25% at
inner face, using refined mesh.

5
 Fig. 9. – Von-Misses stress distribution for
same thickness decrease at outer face. Fig. 11. – Edges stress concentration at
outer face thickness decrease of 10%, on
The FEM simulation of pressure rear inner face.
bulkhead with a repaired area on outer face
with a thickness decrease of 10% presents At outer face, repair effect is slight as the
a stress peak at the proximity of the defect. edges effect on stress. To conclude, 10% of
As result of inertia reduction of the section thickness reduction effect is almost
at this point, membrane stress is expected negligible in front of the edges effect.
to increase as well as bending stress.

Stress concentration at edges

The maximum thickness reduction allowed Lean methodology
during manufacturing is 10 %, and this is
the reference to analyze criticality of the
repairing operation. At inner face the effect Production optimization, from a first
on stress of the repairing operation is slight perspective, is the improvement of
compared to stress concentration at milling productivity in all processes involved in
edges, where stress value is almost the industrialization and manufacturing. Two
double of the value found at defect methodologies were developed based on
surroundings. this principle: TPS and, later on, Lean
manufacturing.
The Toyota Production System (TPS),
originally called just-in-time production, is
an integrated socio-technical system,
developed by Toyota that comprises its
management philosophy and practices. The
Lean manufacturing is a management
philosophy derived mostly from the Toyota
Production System (TPS). The steady
growth of Toyota, from a small company to
the world's largest automaker has focused
attention on how it has achieved this
success, and bigger companies all around
the world try to develop similar
methodologies [5].
Fig.10. – Edges stress concentration at Lean is a production practice that considers
outer face thickness decrease of 10%, on the expenditure of resources for any goal
outer face. other than the creation of value for the end
customer to be wasteful, and thus a target
for elimination. Value, from the Lean
perspective, is defined as any action or
process that a customer would be willing to
pay for.
Both lean and TPS can be seen as a
loosely connected set of potentially
competing principles whose goal is cost

6
reduction by the elimination of waste.
These principles include: Pull processing,
Perfect first-time quality, Waste
minimization, Continuous improvement,
Flexibility, Building and maintaining a long
term relationship with suppliers,
Autonomation (Jidoka), Load leveling
(Heijunka) and Production flow and Visual
control.
Fig. 12 – Component being riveted by an
Another way to optimize is automatize
automatic fastening machine. Courtesy of
through numerically controlled (CNC)
Gemcor
machine tool. While NC tools are controlled
by a computer and can be programmed for Parametric analysis methodology
several jobs, such as: milling, machining or A parametric analysis is realized
drilling. NC tools are not flexible as robotic with the purpose of estimating savings of
arms, but future factories will consist in a automation. Once the structures to
mixture of NC machines, conventional assembly at this machine are selected,
machines and robots. number and type of rivets must be defined.
Robotics provides reduction of direct labor, Due to the difficulty of defining a mean
flexibility to redesign parts, 24-hour cycle time and predicting real machine
operation, performance on hazardous costs, a study of the relationship between
tasks, and a more uniform quality. Despite cycle time and machine costs is required.
of the general cost-reduction oriented
strategy, reasonable robotization could
boost productivity in a mid-term horizon.

Gemcor G-86
implementation at PC-12
Assembly Line

Nowadays, state-of-art aircraft assembly

Fig. 13 – Profitability analysis of LH and RH
lines use automated riveting process. That
PC-12 sidewalls riveting automation.
means that the riveting robot has the ability
to cover the entire fuselage ton from the
outside. Automated fastening proved in to As it is expected to happen, the slower is
be vastly superior in most of its the machine operation the smaller is the
implementations, in quality and speed, to machine hourly cost range. Once the
manual or semi-automatic operations. technological requirements and tolerances
An assembly process is analyzed in order are defined, the appropriate machines
to automate it: right and left sidewalls skin could be selected and the machine hourly
riveting. cost could be estimated.
The high number of similar rivets makes
sidewalls automatic riveting time- Conclusions
consuming and repetitive; these two
characteristics make automation of this
process a good way to increase Continuous improvement methodologies
productivity. must be implemented in order to adapt
A computer-controlled flexible robot is current capacity and resources to demand,
selected for both components in order to predicting bottle necks and reducing waste
reduce timeframes and quality variability. of resources. The proposed methodology
Extra investments are required to Gemcor for waste reduction is Lean, including
G86’s installation and its implementation at Kaizen workshops implementation.
PC-12 line, further profitability research is With these methods, Engineers can
required to justify its use for the Pilatus validate process data in a faster way, take
Aircraft Program at OGMA facilities. decisions, improve systematically and, at
the same time, operations becomes more
reliable, which can ultimately lead to lower
costs and improve productivity.

7
The RPB (rear pressure bulkhead) Sidewalls assembly automation increases
sensibility analysis enables to determine productivity and quality and reduces
the static loads acting on the component timeframes and costs. However, requires
and how defects affect its structural further analysis of profitability and
behavior, as well as understand effects of assembling related issues.
standard rework operations for this type of
component. Even being a conservative References
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is in an acceptable range and maximum
admissible defects don’t change
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