process for evaluation and validation of non-original components for aircraft hydraulic systems

8/20/2019 Process for Evaluation and Validation of Non-Original Components for Aircraft Hydraulic Systems

1/14

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)


2/14

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


3/14

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


4/14

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


5/14

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


6/14

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.



7/14

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


8/14

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.


9/14

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.



10/14

• 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.




11/14

• 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



12/14


• 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



13/14


• 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.



14/14

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.


process for evaluation and validation of non-original components for aircraft hydraulic systems

Documents