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Process for Evaluation and Validation of Non-Original Components for Aircraft Hydraulic Systems
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Transcript of Process for Evaluation and Validation of Non-Original Components for Aircraft Hydraulic Systems
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8/20/2019 Process for Evaluation and Validation of Non-Original Components for Aircraft Hydraulic Systems
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Process for Evaluation and
Validation of Non-OriginalComponents for Aircraft
Hydraulic Systems
Jussi Aaltonen
Originally presented in 4th CEAS Air Space Conference 2013
Jussi Aaltonen, Vänni Alarotu, Kari T. Koskinen (Tampere University of Technology)
Capt. Mika Siitonen (Finnish Air Force Materiel Command)
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Introduction 1/2
• The initial aircraft design goes through long and thorough
evaluation and validation procedures. – Aviation regulating body issues a type certificate, issued by the to
manufacture certifies that the initial design is airworthy.
– Standard airworthiness certificate certifies that the aircraft is
manufactured under the type certificate.
•If type certified initial design is changed – Minor change by type certificate holder - Service bulletin (SB)
– Major change by type certificate holder - Amendment to type
certificate is requested from regulating body
– Any design changes or alterations by any other party –
Supplementary type certificate (STC)• Airworthiness requires usage of original spare- and
replacement parts and following of maintenance programme
and repair procedures specified by the manufacturer.
– All deviations from these are typically considered changes to
initial type certified design 18.12.20144th CEAS Air & Space Conference 2
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Introduction 2/2
• Spare parts which are technically similar than original but
from non-original manufacturing sources: – USA: Formal approval procedure for Parts Manufacturer Approval
(PMA) issued by Federal Aviation Administration (FAA).
– EC: European Aviation Safety Agency (EASA) is taking steps
towards same direction, but currently there are no European
aviation regulations dealing with the matter.• STCs are often needed with aged aircraft types for
conversions to new roles or for just simply keeping them
(more) affordable to operate.
• Evaluation and validation of non-original parts for applying the
STC is in many cases even more complicated process thanvalidation and evaluation of original design
– There usually is no certain knowledge on original design
requirements and specifications available.
– Evaluation and validation programs followed with the original
design usually are at least partly unknown.18.12.20144th CEAS Air & Space Conference 3
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Non-Original Component Evaluation and
Validation Process
• Process is divided into four
distinct phases
• Each phase acts as a prerequisite
for the following phase and also
produces information which
supports making decision
whether to continue to next
phase.
18.12.2014 4
P r e s t u d y
P e r f o r m a n e
T
e s t i n g
E n d u r a n c e
T e s t i n g
C o m p a t
i b i l i t y
T e s t i n g
General Compatibility
Performance Compatibility
Test Program
Tests
Test Program
Tests
Ironbird and Ground Tests
Flight Tests
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Prestudy Phase
• Verification and evaluation of component compatibility and
performance. – General information of the non-original component are gathered
from data supplied by manufacturer or by measuring from the
actual component sample.
– Requirements against which the non-original component is
validated and verified are gathered from technical documentationof the specific aircraft type, general specifications, standards and
usage experiences.
• It is important to notice that:
– There are safety margins already incorporated in the
performance of the original component
– If there is some specific short coming or flaw in the original
component it must be carefully considered whether the
requirements have been originally set too low or the original
component just does not meet the requirements.
18.12.20144th CEAS Air & Space Conference 5
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Performance Testing Phase
• Tests which evaluate and validate that the performance of the
non-original component meets the requirements. – Tests used in the depot level maintenance of the component. It
should however be noted that depot level maintenance tests do
not always test all necessary performance criteria.
• In cases where there will be a significant change in component
design, i.e. operation principle, materials etc., the testprogram must be carefully planned.
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Endurance Testing Phase
• Endurance testing verifies and validates the component
endurance and life-time in the specific application. – Reliability of the component is at least on the level of the original
one and that it does not cause any flight safety risks.
– Components usable service life fits to maintenance schedule and
targeted availability.
–
Planning of the endurance test program requires extensive andprofound knowledge on the aircraft and its typical usage.
• Sometimes accelerated life testing can be used to simulate
complete component lifecycle
– Result of the accelerated test can be then compared to
experiences on the original component in the specific aircraft.• Usually comparative test, where original and non-original
component are compared against each other, are used.
– Both components are run under same load and stress spectrums
for specified time after which the wear and tear of them is
measured18.12.20144th CEAS Air & Space Conference 7
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Compatibility Testing Phase
• Final actions towards airworthiness.
– Component compatibility with aircraft systems is tested first byground testing and finally by flight testing.
– Due to extensive bench testing prior to this phase ground testing
can mainly concentrate on general systems and mechanical
compatibility issues.
–
After successful completion of ground tests it is possible to enter flight testing.
• Planning the flight testing program must be done considering
the lifecycle of the component in the specific usage.
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CASE: Twin Engine Aircraft Hydraulic Pump 1/5
• Non-original pump originates to another aircraft of the same
type and same manufacturer but which is targeted to differentcustomer base.
– It is designed to meet general aerospace specifications as well as
manufacturer specific specifications but customer specific
specifications may differ.
•
Comparison of available technical data available and studyingsamples proved that the non-original pump was very similar to
the original one and there is no need for any additional design
changes related to changing the hydraulic pump type.
• Basic performance characteristics of both pumps were
compared by a set of tests ran in the test bench resemblingvery closely the one specified for pump depot level
maintenance testing.
– Test sets were designed to reveal out any fundamental
differences critical to specific application.
18.12.20144th CEAS Air & Space Conference 9
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• Dynamic characteristics of pumps
and their regulators were studied insecond test set by inducing fast flow
demand changes of variable
magnitude
• As a result of the first test set basic
performance characteristics such as
could be compared: – Pump efficiencies
– Controller operation and response
curves
– Delivery and drain flow rates
– Level of delivery pressure pulsation
– Case drain flow dynamics
• Testing minimum supply pressure
was moved to be tested in later
stage due to the fact testing it
inevitably causes damage to pump.
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CASE: Twin Engine Aircraft Hydraulic Pump 2/5
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• Hydraulic pump lifetime in real application is far too long to be
reasonable to be replicated in laboratory tests and hydraulicpump also is too complicated piece of machinery to undergo
any kind of accelerated life test with satisfying reliability.
• Therefore a comparative testing approach was chosen.
• Load spectrum generation
– Simulations using combined hydraulic system and flightsimulation model to find out operating points where the load for
the hydraulic system and particularly for the pump is the harshest
– Load spectrum used was generated by extracting flight control
system commands related to continuous 8 min aerobatic
maneuvering from real mission data and running them through thesimulation model to translate them to corresponding hydraulic
system flow demands.
– Endurance test used this load spectrum as a continuous loop.
• Maximum length of test was set either to hydraulic pump
service interval, or to malfunction or failure.18.12.20144th CEAS Air & Space Conference 11
CASE: Twin Engine Aircraft Hydraulic Pump 3/5
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CASE: Twin Engine Aircraft Hydraulic Pump 4/5
• Goal was to find out if there is a
significant difference in between thereliability and life time of pumps and
if there is any differences in how
their performance evolves during
long usage time in harsh conditions.
•Also the minimum supply pressuretests were incorporated in this test
since load spectrum naturally
included several points in every
cycle where supply pressure drops
down to zero.• Wear on critical wear surfaces was
measured as weight loss
• Change in overall performance
measured as efficiencies
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CASE: Twin Engine Aircraft Hydraulic Pump 5/5
• Due to harshness of load
spectrum used neither of pumpsreached full time but tests ended
prematurely to minor failure
(leakage) in both cases.
• After successful completion of
endurance testing phase follows
the final compatibility testing. – Short ground test program
hydraulic systems.
– After successful completed
follows flight testing.
• Upon completion of the process
the non-original pump will be
qualified to be used as a spare
part in any combination with the
original one.
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Conclusions
• Purpose of this research was to develop and pilot the evaluation and
validation process which can be applied in STC approval process ofany aircraft mechanical or electro-mechanical component.
• The process was developed and it was proven to be reliable, effective
in the terms of both costs and time.
• It is noted that even though this process is cost effective and straight
forward it still requires extensive expertise on the specific aircraft
type and aircraft systems and components in general.
• Importance of experience base and research data gained in earlier
systematic research programs cannot be overlooked since
developing for example advanced simulation models is hardly
justified for the sole purpose of a single spare part evaluation and
validation.• The process developed can also be used as an effective tool in
comparative testing involved in FAA’s PMA procedure and probably
also in future EASA replacement part procedure.
18.12.20144th CEAS Air & Space Conference 14