Takeoff derate setting time limit

[JammedStab]

According to a particular AFM, takeoff derate settings are time-limited to 5 minutes. Is it possible that MCT or climb thrust is actually a higher thrust setting?

[Denti]

Depending on engines, derates etc it is absolutely possible. And time limits are probably just an issue of paying the right amount of money to the OEM.

[c100driver]

Time limits are an AFM purchase options when the aircraft is spec'd with the first owner/operator.

You can have 5 minutes free or an option of 10 minutes for xxx$

It is possible to buy the AFM supplement to change the time limit after delivery but it is a lot more $$$.

[The Dominican]

JammedStab
Takeoff derate setting time limit
According to a particular AFM, takeoff derate settings are time-limited to 5 minutes. Is it possible that MCT or climb thrust is actually a higher thrust setting?


In the case of the 76 derate power setting are in fact lower than MCT, it really only should apply to MAX T/O, but I'm a well trained monkey and I do what I'm told....!;)

[tdracer]

JammedStab
It's a generic limitation - 5 minute takeoff. 5 minutes is the baseline cert basis for the engine (limits analysis and the such). Since a derate can be anything from a few percent to 40 percent (depending on the engine/aircraft), it's simpler to just maintain the same limitation without attempting to determine if the derate drops it below the max climb/con rating.
As C100driver notes, most aircraft/engine combinations have "10 minute takeoff" as an extra cost option. However, at least according to Pratt & Whitney, you're only allowed to use 10 minute takeoff if an engine has already failed (it has to do with the engine life limit analysis - basically it's assumed that the actual use of 10 minute takeoff will be really rare).

[Skyjob]

According to a particular AFM, takeoff derate settings are time-limited to 5 minutes. Is it possible that MCT or climb thrust is actually a higher thrust setting?

Two things confused here.

The 5 minute (or 10 if purchased as described above) limitation applies to FULL TO thrust. The 5 minute limitation must be observed in all takeoffs due to fact one can select full power in some scenarios.
Any derated/assumed takeoff settings are engine thrust reduction techniques, so hence it is possible that the MCT is higher than your TO thrust used, but only in those cases where used.


It cannot be overemphasised that the limitation is applicable to FULL TO thrust.
Any reductions to that FULL TO thrust are saving your engine working too hard for too long, enhancing its lifecycle.

Finally, if you experience an engine failure, flying an engine out procedure, remember this is procedure designed to take into account the limitation as above, either 5 or 10 as purchased.
This thus requires crew to be aware of the time after which (even if not yet having completed the escape manoeuvre) to select MCT. Many crew in the simulator are oblivious to this fact as they tend to practise EO which achieves Flap Up selection and MCT selection within 5 minutes. When faced with the time limitation (due required turns, very heavy weight, a higher MFRA than standard, etc), many crew forget the time limitation and it becomes a nice discussion point afterwards.

[Lord Spandex Masher]

It cannot be overemphasised that the limitation is applicable to FULL TO thrust.
Any reductions to that FULL TO thrust are saving your engine working too hard for too long, enhancing its lifecycle.


It should really be applicable to anything over MCT though.

[FE Hoppy]

This thus requires crew to be aware of the time after which (even if not yet having completed the escape manoeuvre) to select MCT. Many crew in the simulator are oblivious to this fact as they tend to practise EO which achieves Flap Up selection and MCT selection within 5 minutes. When faced with the time limitation (due required turns, very heavy weight, a higher MFRA than standard, etc), many crew forget the time limitation and it becomes a nice discussion point afterwards.

I'd like to know on what basis any OEI procedure has the aircraft not clean and VFTO by the time the 5/10 minutes is up?

The only one I can think of is a wrongly calculated take off weight.

[FlyingStone]

Finally, if you experience an engine failure, flying an engine out procedure, remember this is procedure designed to take into account the limitation as above, either 5 or 10 as purchased.
This thus requires crew to be aware of the time after which (even if not yet having completed the escape manoeuvre) to select MCT. Many crew in the simulator are oblivious to this fact as they tend to practise EO which achieves Flap Up selection and MCT selection within 5 minutes. When faced with the time limitation (due required turns, very heavy weight, a higher MFRA than standard, etc), many crew forget the time limitation and it becomes a nice discussion point afterwards.

Given that (at least with Boeing) the swich from 5 minute to 10 min T/O thrust limit is only a paper (and money) exercise, the 5 minute limit shouldn't be understood as hard limitation. And since the aircraft doesn't need to be modified to be able to sustain 10 min T/O thrust (of course only in case of engine failure as mentioned by somebody else), the engine won't sieze at 5:01 just because you don't have the correct AFM Appendix. In my opinion it's much more important to have the aircraft at a safe attitude and position (lateral and vertical) before reducing the thrust to MCT. Engine failure is an emergency situation anyway, which grants commander exemptions from most of the aircraft limitations, as long as it's benefitial to the safety of the aircraft and its occupants.

[bucks_raj]

The ATR by virtue of the ATPCS is certified for a

T/O power 2475 SHP for 5min

which is lower than

MCT 2500shp .. Time Unlimited

The restriction comes as a regulatory requirement where T/O power needs to be certified for 5min

Usually all T/o ratings are lower than MCT arent they??

[Skyjob]

Lord Spandex:
It should really be applicable to anything over MCT though
Which is why I wrote it only applied to MAX TO. Any assumed or reduced thrust may enable TO thrust below MAX TO to be used. It is well beyond the scope of pilots and performance engineers to take all possible combinations of thrust into account so only the MAX TO is assessed. Some cases result in a reduced TO still above MCT, but most are not.

FE Hoppy:
I'd like to know on what basis any OEI procedure has the aircraft not clean and VFTO by the time the 5/10 minutes is up? The only one I can think of is a wrongly calculated take off weight.
Think of a maximum takeoff weight at a high pressure altitude on a hot day, a very high (well above standard) MFRA, with extended turns to enable you to establish on a straight and level segment prior to acceleration. This is the same reason why the 10 minutes if offered to some operators because they NEED it. In EU-area, generally and in terms of performance issues, terrain does not pose many problems, but in other areas of the world this can be more challenging.

FlyingStone:
Given that (at least with Boeing) the swich from 5 minute to 10 min T/O thrust limit is only a paper (and money) exercise, the 5 minute limit shouldn't be understood as hard limitation
The 5 minute should be treated the same as the 10 minute limitation, your AFM does not tell you about the 10 minute allowance, it only tells you about the 5 minute if the engine is classed as such. I agree it does not make a difference as the engine is capable of using it for 10 minutes, but that is another issue. You may only use it when authorised to do so.
If manufacturer has a maximum structural takeoff weight for an aircraft by design but your operator is certified to use one 20 tonnes lower ($$$), would you go over the company imposed limit on that? Think of the same way with the 5 minute, your company has paid for 5 minutes, you do not get 10, although capable of it.

bucks_raj:
Usually all T/o ratings are lower than MCT arent they??
Opposite way around on a jet engine usually, TO trust is usually higher than MCT, hence the limitation.

[FlyingStone]

If manufacturer has a maximum structural takeoff weight for an aircraft by design but your operator is certified to use one 20 tonnes lower ($$$), would you go over the company imposed limit on that? Think of the same way with the 5 minute, your company has paid for 5 minutes, you do not get 10, although capable of it.

When you're on the ground doing load calculations, you are not in emergency situation and you have to obey all the dispatch limitations - 5-min T/O thrust (if you don't have the 10-min version), W&B, etc. But once you are in emergency situation (e.g. engine failure) the rules change and you don't have to oblige to them so strictly. I'm not saying you should push the engines for 10 minutes at TO thrust if you have engine failure as an SOP. Just focus on flying first and do it when you have time and the aircraft is stable in it's attitude and flight path (after turn for example) - even if thrust reduction to MCT is after 6 minutes instead of 5.

Since you bring up the W&B issue. What if you have an engine fire after takeoff that cannot be extinguished? Will you go to holding to burn enough fuel to get you below MLW or land ASAP?

[john_tullamarine]

I suggest that the 10 minute rating cost is not for that simple change but, rather, for the set of OEI charts taking credit for the revised limit which come along for the money ...

In anger, with 5 minute charts, one probably wouldn't be too worried if T/O thrust is held on a bit longer in the event that things weren't proceeding according to plan ...

[FE Hoppy]

FE Hoppy:
Quote:
I'd like to know on what basis any OEI procedure has the aircraft not clean and VFTO by the time the 5/10 minutes is up? The only one I can think of is a wrongly calculated take off weight.
Think of a maximum takeoff weight at a high pressure altitude on a hot day, a very high (well above standard) MFRA, with extended turns to enable you to establish on a straight and level segment prior to acceleration. This is the same reason why the 10 minutes if offered to some operators because they NEED it. In EU-area, generally and in terms of performance issues, terrain does not pose many problems, but in other areas of the world this can be more challenging.


No.
Firstly, there are plenty of terrain limited runways in the EU thanks. Also some of us have operated in many other parts of the world.

Now I ask again. When is a take of weight ever calculated based on the presumption that the aircraft will not be correctly configured at the end of the take off thrust time limit?

Correct answer: never.

[Skyjob]

FE Hoppy:
Correct answer: never.
And that is where you are incorrect.
Some destinations even make specific mention of the fact that this cannot be achieved in certain conditions.
That's exactly where I am talking about.
Operating in those fields benefits greatly from the 10 minutes but even then will not guarantee a completed configuration after 10 minutes hence the notes on the charts.
I hope you will benefit flying into these destinations one day so you can (then) agree with me.

FlyingStone:
What if you have an engine fire after takeoff that cannot be extinguished? Will you go to holding to burn enough fuel to get you below MLW or land ASAP?

An overweight landing is always allowed subject to conditions, the one you mentioned falls in my book as one of them, like yours!

[tdracer]

One other aspect of the '10 minute TO' is that many engines have a higher EGT redline for TO than for Max Con - and that's programed into EICAS (or whatever system displays EGT on non-Boeing). So at the end of 5 minutes, there is the chance your EGT could turn red if you don't have the 10 minute TO option.
BTW, if memory serves, on the 747-8 we made 10 minute TO baseline, not an option.

[FE Hoppy]

Skyjob
FE Hoppy:
Quote:
Correct answer: never.
And that is where you are incorrect.
Some destinations even make specific mention of the fact that this cannot be achieved in certain conditions.
That's exactly where I am talking about.
Operating in those fields benefits greatly from the 10 minutes but even then will not guarantee a completed configuration after 10 minutes hence the notes on the charts.
I hope you will benefit flying into these destinations one day so you can (then) agree with me.

Would you mind telling me which destination?
And which authority lets you operate outside of perf A "in certain conditions"?
And what those conditions are?

I would like to benefit from your insight whilst waiting for the opportunity to fly into these destinations!