CFM56

[bigbrother]

Tech question without notice. Flex take off power. Are you required to comply with the 10Min engine out time limit, based on Take off Thrust, even though you are taking off with a reduced power? Given that at a Flex power setting, all parameters are below the 925C, 101N1, etc.... (for the sake of argument) are you required to then bring the thrust levers back to climb?

Its not that you would leave them there forever perse, but just say you went to 12 minutes, any issues?

[rudderrudderrat]

Hi bigbrother,
Affirm. You are expected to limit take off power for 10 mins (even flex). To keep things simple, we only have one approved procedure to comply with the 10 minute limitation.

Sometimes, our flex is the same as climb power, and therefore MCT would be an increase in power.

[Cough]

Flex can be anything from a .1% below TOGA power to (as rudderrat says) climb power. As you don't know where you are in the scheme of things the 10 min limit applies.

Say you happened to use 12 in order to 'save life', I doubt anyone would have an issue. If you used it to give yourself a warm fuzzy feeling then I would suspect that you would be walking...

Just remember, just because it is certified to do it, doesn't mean (for instance) that you should. The 'good' engine, for example, might have also swallowed a bird and lowering its stress levels may be wise.

[B737900er]

I was told its a 5min restriction, and the 10 min limit is a customer option?

[Denti]

That is correct. It is 5 minutes as standard but 10 minutes if you pay for it, which many airlines do (or get for free in a larger order).

Flex is the airbus term, on the boeing we can go considerably below climb thrust for take off reduction and routinely do so, however the 10 minute (in our case) limit still applies. "Reducing" to MCT would in fact increase the thrust considerably.

[HazelNuts39]

I would think that you can schedule flex takeoff power for unlimited duration if you can verify that it is less than the Max Continuous power for the actual temperature, provided there is no automatic system that looks after the 10 minute limit.

Strictly speaking the RPM and gas temperature limits are subject to the time limitation of 5 or 10 minutes, not the power or thrust as such.

[BOAC]

H39 is spot on - if the flex is = or below MCT you can go on - for ever.:) For any other factors, you use what you need to avoid crashing and argue later. The engine will not disintegrate at 5:01 or 10:01.

[barit1]

As a point of reference - and I'm speaking only of mechanical integrity - I used to conduct engine runs on the "test bench" (test cell) with the following schedule:

Startup, mechanical check, then push up to MCT for 5 minute warmup.

Advance to the highest TO rating, hold for 5 minutes, record data.

Retard to the next lower TO rating, hold for 5 minutes, record data again.

Repeat, stairstepping down to each lower rating and taking data again.

The total run might take 90 minutes, with half of that never below MCT. We never had any sign of mechanical distress in nearly ten years of this schedule, although some performance loss was to be expected.

My point is merely that the 5 / 10 minute certification limit is to keep everyone on the up-and-up, but the engine can run well beyond this "limit" without fear of failure - so long as rpm and temp etc. limits are observed. :ok: