Flight testing after engine changes.

[Tenlavs]

I would be grateful for some help for researching the answer to a "what-if?" from my boss.

I fly an old 4-jet for the military and often have to perform the post-maintenance airtest. Each airframe is given a 'major' service about every 6 years, which takes 4 months and is quite an invasive process. I believe the civil terminology is a D-check? All 4 engines are removed and often, but not always, any combination of engines may then be changed depending on other criteria. After a major there is a 4-hour airtest to be flown, a small part of which includes individual engine slam-acceleration tests and shutdown/relight tests. The engine tests take place regardless of whether any of engines have been changed for new units.

Between these majors there is also 'minor' service, which sometimes requires engines to be removed/re-fitted or changed. We have a regulation that requires the aircraft to be flight-checked after a double-engine change and therefore the slams, relight checks etc are performed on the new engines. Traditionally we have treated the removal/refit of an engine as a 'change', on the basis that the integrity of the unit has been disturbed. So the removal and refit of 2 engines would generate the requirement for an airtest. There is no requirement to airtest an aircraft after a single engine change, and it goes straight back into normal service.

For financial reasons we have been asked to consider dropping the requirement to airtest the aircraft after the removal/refit of engines and to regard only the fitting 2 or more new engines as triggering an airtest. If we went down this route, the worst case scenario could see an aircraft have 3 engines removed/refitted and the 4th changed, before being be released straight back into service with only ground checks.

I am curious to know how other civil or military aircraft are managed in equivalent circumstances. It is possible that we are being too cautious or maybe we are following normal practice, particularly for older types?

Do other organizations/companies require a flight test of aircraft after multiple engine changes?

Do other 4-jet operators (particularly older types) have similar, or perhaps much more lenient, requirements?

Is the removal and refit of an engine regarded as equivalent to a change by anyone else?

Many thanks in advance.

[BelArgUSA]

I have occasionally flown "flight tests" after major maintenance... such as "C" or "D" checks (I fly 747-200s) - problem is - I never asked if required, or necessary to do such... They tell me "you are scheduled for a flight check tomorrow at 1600, of aircraft OPA, parked on maintance ramp... - I do it..." - Then the next day they give me a flight check test items list, such as shutdown and flight starts, or alternate gear extension, etc... Fun flights anyway, sometimes takes 2 hrs in the air... for ridiculous little things (toilet flush cycles at FL 150...)
xxx
For certain (I think), a flight test is required when major maintenance is performed to control surfaces. As to for engine changes, I am not too sure if required or not. I remember a 3 engine ferry I did long ago (engine failure with severe FOD, big birds in nº 4 motor, fire warning and fire bottle discharged), we flew the plane back to Europe, and got another engine installed. The next day, we flew a live trip with cargo payload, no flight test... All I remember, is that we double-checked the nº 4 before takeoff...
xxx
For you in the UK, and military, might be different standards too...
xxx
:)
Happy contrails

[G.O.G.]

Cant see any need for air tests after engine changes as long as you give them a good old thrash during ground runs making sure engines meet all parameters.
Its a nice day

[Speedbird48]

In days long ago when we had big round engines and long inline ones as well, we did indeed do a flight test after an engine change. But, I don't recall ever doing one on a jet for just an engine change.

These days turbine engines stay on the wing for so many years, and modules get changed in situ, so it is a whole different ball game. It all gets done at the run-up pad.

However in your case with several, or all, engines being off at once and being put back together I would think it was a prudent thing to do.

The wonderful Iron Duck, memories!! I believe you still have the 4 survivors of the ones that I flew in Africa??

Speedbird48

[sycamore]

Perhaps, in the interests of financial belt tightening you might ask the `engineers`/bean counters to leave off bits,or leave on bits that are past their `sell-by` date.In whose financial interest is it ,not to do an airtest ? Is the `Company` generating that ,or is it the client ? Who is the client ? Maybe the company want to short-change the client, by missing out parts of the airtest--- why bother, just wheel it out of the door,guarantee runs out at `brakes-off`..
Older aircraft/engines/systems are not the same on modern jets ,with Fadec/ums/ downloadable diagnostics,and where they are not subjected to unusual operating conditions.Nowadays, most engines are podded, and replaced as such, and usually run one `cycle` per flight, left at constant power,and in non-hostile environments( ie over the sea at low levels, dusty ,etc) so there is perhaps not the need to do extensive engine airtests.
Then there is always the possibility that there may be an in-flight shut-down
,for operational reasons,and therefore a need to restart in flight. Relights on the ground are not the same as relights in flight !!
The bottom line should be that the `engineers`/bean-counters /company should understand that if an a/c is taken apart and put back together, even with all the same bits, it is a new a/c...
Ask for volunteers from the appropriate departments to go along on the next airtest...I guarantee you won`t have many takers.....Remember, it won`t be their necks on the line if anything should happen when it`s returned to the client....it could be yours..........From your initial query i take it you are not ex-mil, perhaps even your boss ? Who do you work for ? you may even be `the financial reason` ie if we don`t do a full airtest then we don`t need that many pilots.. more money saving ideas !!!! go carefully.. pm if you can..

[Genghis the Engineer]

Venturing a semi-uninformed opinion here. Is it not reasonably possible to evaluate integrity aspects of the engine change in ground test, and then on the next normal scheduled flight, to include a climb profile against which engine performance can be evaluated against the ODM? Thus providing a high level of validation of the engine, with minimal extra flight time?

G

[A2QFI]

GOG your engineering terminology re "Giving an engine a good thrash" comes across as amateur or even ignorant! Nothing you do on the ground will tell you if an engine will accept an idle to full power slam at 170 kts, 40K feet and -60C. I appreciate that I am talking about military engine air tests with which I am familiar and know that this is not the sort of treatment that would given to an airliner!

[On-MarkBob]

I civvy street, an annual airtest is carried out for the authorities. This is to alert them of any degrading trends. I have often been asked by the Authority to have an aircraft re-weighed due to a downward trend in performance.
Airtesting the aircraft after an engine change is done for the same reason. A simple timed climb to hight will show if the engine is producing the real goods. Even if the engine has been brake tested, disturbing its 'arteries' and controls can often give rise to a lack of power or other problems. Dirt in the system etc. I airtested an aircraft once that had an engine change and a generator had been fitted with the studs in the wrong wholes. On any other aircraft it might have been ok but this one had a problem with the throttle linkage which for some reason only became apparent in flight and prevented the application of max power.
Lastly, Air testing is always a good idea after any major operation, so to speak, it means an experienced guy gets the first go and is expecting that something might go wrong. To suddenly 'present' an aircraft to a line pilot after major work, the risk is almost certainly greater. That's why the Authotities have pilots approved for air testing! It just makes good sense.

[smudgethecat]

In the civilian world a air test is not required after a engine change, what is required is a full power run to ensure all parameters EPR/N1 ,EGT ,vib levels etc etc are all within the normal limits and that all associated systems are functioning normally, of course that does not mean a company could make a air test a "company requirement" but ive never heard of it, the only thing there normally interested in is getting it back into service asap

[Kitbag]

In the UK mil environment the requirement for engine air test following replacement or even adjustment is dictated by the individual Engineering Authority. Primary drivers are the performance of the engine at the extremes of the aircraft operating envelope, thus relight performance high and slow, slam from idle to max military power, fuel flows at altitude etc. Effectively things which cannot be confirmed on the ground. The main difference of course is the military engine is required to cycle rather more often per sortie and potentially needs to be operated closer to the limits than civ engines. I have known cases where early in a types life far more flight (and ground) testing was carried out than when the aircraft was more mature, reflecting increases in operating knowledge and commensurate increase in confidence regarding equipment performance and reliability. In answer to the question, in the UK mil it depends, but the decision is made by the engineers- this is flight safety we are talking about.

[Bodjit]

Hi, I've had experience of both, whilst in the military after an eng replacement we always did an airtest iaw the AP 5M flight test manual (oh the good ol' days).
Now I'm a licensed engineer we do full power ground runs then hand it over back into revenue service. The only exceptions to this are after big checks as dictated by the Maint manual which I think says an airtest or handling check (theres a difference) is reqd if a number of engs/ control surfaces have been removed/refitted/replaced.
Its an expensive game flight testing Ac, and as we all know the military has deep pockets. I'm on 4 eng ac at the moment. hope it helps
bodjit

[jettison valve]

Looking at the currently running A330/A340 elevator SCU retrofit programme, I am still unsure whether it is a good idea to take all for of them out at the same time, modify them, and reinstall them - and no test flight is conducted afterwards.
The AMM is kind of vague concerning such a job (I mean the testflight...;)), and it is the understanding of various engineers that you don´t need a "live" test in the air... :confused:

Cheers,
J.V.

[Daysleeper]

n the civilian world .....what is required is a full power run to ensure all parameters EPR/N1 ,EGT ,vib levels etc etc are all within the normal limits
Though in the UK it would appear that no full power engine runs are required...:eek:
From AAIB report (http://www.aaib.dft.gov.uk/publications/bulletins/august_2007/boeing_767_31k__g_dajc.cfm)

After the passengers had disembarked, an engineer
boarded the aircraft and informed the flight crew that
the replacement left engine had not been subjected to
hgh-power ground runs because it had been suppled
“pre-tested”.

[mono]

After the passengers had disembarked, an engineer
boarded the aircraft and informed the flight crew that
the replacement left engine had not been subjected to
hgh-power ground runs because it had been suppled
“pre-tested”.

Not too sure I believe this. There would still be a requirement to check to at least part power in order to confirm the correct rigging.

However, there is still the possibility that the smoke wouldn't have been detected as quite often we check the engines with the bleeds off as per MM requirements.

My response to the posters question is that in civvy street we carry out ground runs only. Full power or part power according to the AMM regarding the circumstances of the change. This may include slam checks and, if adjustments are required a couple of shutdowns and re-lights. We do not however carry out an air test simply because of an engine change.

[Dr Illitout]

If an engine is supplied test cell run then the approved MM on the FADEC equiped Boeings I work on says that you need only to do a idle leak check before releasing it to service. On the older Boeings there is of course the part power checks and the take off power checks to do. This may differ from operator to operator though. I personaly like to make sure that the engine accelerates and it can go into reverse.
My logic being is if the engine won't go to full power the pilot will abandon the take off and come back to kick my a***e. Embarrassing but not tragic. If the engine won't go into reverse on a wet, short runway that is a whole new leval of embarrassment!
I have never changed all four engines at once though and the times I've changed both on a twin we did an airtest but that was part of the refurbishment we did any way.
Rgds Dr I

[Piper19]

After an engine change, we (mechanics) do a full power engine run to check the whole engine, parameters, but also systems connected to engine (generator, bleed,...). If the fan blades were removed/replaced/reshuffled we also compute the balance weight that has to come into the spinner and do a vibration test. That's all. If all within limits, safe to release to normal service.
If ,however, a certain parameter is not ok, we spend a long time on the engine ground run, which can burn a lot more fuel than a 2 hour flight, due to the testing at max power.
On the aircraft I work on there are over 16 differnet engine tests described in the MM. For example high power, part power, idle run leak check, health check, vibration run,...

[OCCWMF]

These bean stealers have possibly made the assumption that:

Air-test costs = £x
No. of incidents following engine remove/refit/change = 0 or negligible
Therefore £x expenditure not required.

Slightly flawed. Perhaps they should report to their superiors that the money they are spending on engineers appears to be well placed. And as the aircraft gets older you are likely to encounter more problems, not fewer.

IMHO ;)