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Gas turbine engine MTBF ?

Old 6th Feb 2011, 17:03
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Gas turbine engine MTBF ?

Dear colls,
does anybody know approximately what is the MTBF for a gas turbine engine like those of B737 A320? The type of failure should be total loss of thrust.
Thank you in advance for your answers.
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Old 8th Feb 2011, 12:50
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Total loss of thrust would be the result of a catastrophic failure, maybe due to FOD or a major component breakage. Because engines are designed for this not to happen if at all possible, MTBF figures are not relevant. You are talking random events for which statistical failure rates are not applicable.

You may be able to look at birdstrike rates but that would vary by aircraft type and location, again not really MTBF though.

Most engine removals are for deteriorated thrust rating or EGT margin. Modern engines are getting towards 30,000 hours on wing and if I remember corectly the old Concorde Olympus were more like 300!
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Old 8th Feb 2011, 18:31
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Engines do time out, allot of wear and tear on internal components, bearings etc between the 7-12k hour range is usual time in service for a healthy engine before it comes off wing. Normally a comprehensive examination process done between operators and engine manuf. to determine a safe off the wing time.
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Old 8th Feb 2011, 21:37
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Cool

RB211-535 19,000 hours average time to first shop visit, The RB211-535E4 achieved the world record for on-wing life without removal for over 40,000 hours over nine years in operation for a 757.
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Old 8th Feb 2011, 22:35
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I think the pratt on the 752 comes off wing about 6-7 k/hrs. They supposedly save a bit of fuel but the overhaul cost's make them less preferred, heard they are not fun to work on as well. We have been putting 752-f's into service like crazy and I think we just put our first pratt powered one in. Suppose I shall find out for myself soon enough. The reliabiity on the rolls has been pretty good, I like looking at them on an engine stand, they just look soo clean as compared to a cf6, less monkeymotion.
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Old 10th Feb 2011, 20:08
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Yeah I agree about the life before an engine is rebuilt and taken off the wing but I needed some statistical information for MTBF and I found something in EASA :

CS-E510 (g),(2)
(g) For compliance with CS-E, the following Failure definitions apply to the Engine:

(1) An Engine Failure in which the only consequence is partial or complete loss of thrust or power
(and associated Engine services) from the Engine must be regarded as a Minor Engine Effect.


(2) The following effects must be regarded as Hazardous Engine Effects:
(i) Non-containment of high-energy debris,
(ii) Concentration of toxic products in the Engine bleed air for the cabin sufficient to incapacitate
crew or passengers,
(iii) Significant thrust in the opposite direction to that commanded by the pilot,
(iv) Uncontrolled fire,
(v) Failure of the Engine mount system leading to inadvertent Engine separation,
(vi) Release of the propeller by the Engine, if applicable,
(vii) Complete inability to shut the Engine down.


(3) An effect falling between those covered in CS-E 510 (g)(1) and (2) must be regarded as a Major Engine Effect.

(3) It must be shown that Hazardous Engine Effects are predicted to occur at a rate not in excess of
that defined as Extremely Remote (probability less than 10-7 per Engine flight hour). The
estimated probability for individual Failures may be insufficiently precise to enable the total rate
for Hazardous Engine Effects to be assessed. For Engine certification, it is acceptable to consider
that the intent of this paragraph is achieved if the probability of a Hazardous Engine Effect arising
from an individual Failure can be predicted to be not greater than 10-8 per Engine flight hour (see
also CS-E 510 (c)).

(4) It must be shown that Major Engine Effects are predicted to occur at a rate not in excess of that
defined as Remote (probability less than 10-5 per Engine flight hour).

λ=0,00001 failure/ 1hour=10/106hours=10FPMH
MTBF=1/ λ=100000hours
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