B757 Assumed temperature T/O thrust time limit?
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From the nice people at the FAA (I'm sure similar language can be found around the world):
This would mean any thrust higher than MCT has a "restricted period of use". But if you want to trash the engines and then wonder why you have the highest IFSD tally at your company, go on ahead.
"Maximum continuous thrust", with respect to turbojet engines, means the maximum jet thrust that is developed statically or in flight, in standard atmosphere at a specified altitude, within the engine operating limitations established under Part 33, and approved for unrestricted periods of use.
What I am saying is that the Boeing limit is an EGT limit, not a thrust limit. Airlines then convert this limit into an SOP. The airline I work for its the same as most other airlines. TOGA thrust for 5 mins. But that has not come from Boeing, its come from the airlines. The EGT limit for MCT is 790 according to that chapter. I said you COULD argue (not that I WOULD) that you were not at the limit, so a time limit would not apply, but we are now into the realms of legalese.
Back to the OPs question. TOGA is for 5 mins, derate isn't. If you now want to know if the derate thrust setting is above MCT you would have to select CON on the TMSP and see what its giving you, or look it up in FCOM1. You would then have to make a decision. Do we not think this is slightly unfeasible during a V1 cut, maybe in the middle of an emergency turn or dealing with a terrain issue? It seems, having spoken to other 757 operators that Boeing thinks so, and that the SOP in most airlines is that if you select TOGA you have a time limit, if you remain at the derate setting then you do not. If your training department says otherwise that you will have to go with what they say. But I would probably question their priorities.
Back to the OPs question. TOGA is for 5 mins, derate isn't. If you now want to know if the derate thrust setting is above MCT you would have to select CON on the TMSP and see what its giving you, or look it up in FCOM1. You would then have to make a decision. Do we not think this is slightly unfeasible during a V1 cut, maybe in the middle of an emergency turn or dealing with a terrain issue? It seems, having spoken to other 757 operators that Boeing thinks so, and that the SOP in most airlines is that if you select TOGA you have a time limit, if you remain at the derate setting then you do not. If your training department says otherwise that you will have to go with what they say. But I would probably question their priorities.
TOGA is for 5 mins, derate isn't.
As long as you think its required. Or would you disagree with that?
Maximum Continuous is the Maximum you can use Continuously.
A 34 deg Assumed Temp might only be a couple of %N1 less than TOGA- WAY above MCT. And you think there is no time limit on that?
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Do you really believe that Chapter 1 Limitations, 1.7 Engine, 1.7.2 EGT limits is saying the material used for the turbine blades is happy for continuous use at 849 degs C?
(In fact, I'd argue that one cycle of 30 minutes is less fatique than 6 cycles of 5 minutes.)
The 5 (or 10) minute regulatory limit is plainly outdated in light of modern materials and technology. Instead, it serves a convenient CYA function for manufacturers.
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A 34 deg Assumed Temp might only be a couple of %N1 less than TOGA- WAY above MCT. And you think there is no time limit on that?
Do you really believe that Chapter 1 Limitations, 1.7 Engine, 1.7.2 EGT limits is saying the material used for the turbine blades is happy for continuous use at 849 degs C?
As for assumed temperature take offs, here's the deal: there is no requirement for you to use TOGA thrust to meet the performance climb gradient. Therefore you do not need to select it. If you do select it there is a time limit on its use, and after 5 or 10 mins you should select MCT (or CON). Even if you are using an assumed temperature for take off you should select CON after 5/10 mins or after the acceleration phase as per your airlines SOP.
HOWEVER, if you get to 5 or 10 mins and you feel you need to use it for a longer period of time then USE IT! Who gives a rats about the time limit. Take heed of this wizofoz, or you may need to reassess your priorities.
What I was trying to convey, was that there is nothing written that specifically applies a time limit to any power setting other than TOGA. We all know whats implied by the use of the words Max Continuous Thrust, but by the strict letter of the book it is a time limit of 5 or 10 mins at an EGT of 850 deg C.
If someone can provide a Boeing FCOM reference that says otherwise I'm quite happy to say I'm wrong.
Just to go back to the OPs original question.
If your airlines has no SOP about using TOGA (or any setting above CON) in the event of a longwinded emergency turn, then I suggest you ask what they want you to do.
My suggestion would be to leave TOGA (or any setting above CON) where it is until A) you are above MSA, or B) terrain separation is assured or C) the emergency turn is completed.
Would anyone disagree with the above? Or would we all like to hit the hill, but have nicely under stressed engines?
Practicalities ladies and gentlemen.
If your airlines has no SOP about using TOGA (or any setting above CON) in the event of a longwinded emergency turn, then I suggest you ask what they want you to do.
My suggestion would be to leave TOGA (or any setting above CON) where it is until A) you are above MSA, or B) terrain separation is assured or C) the emergency turn is completed.
Would anyone disagree with the above? Or would we all like to hit the hill, but have nicely under stressed engines?
Practicalities ladies and gentlemen.
there is no requirement for you to use TOGA thrust to meet the performance climb gradient.
Even if you are using an assumed temperature for take off you should select CON after 5/10 mins
HOWEVER, if you get to 5 or 10 mins and you feel you need to use it for a longer period of time then USE IT!
there is nothing written that specifically applies a time limit to any power setting other than TOGA.
We all know whats[sic] implied by the use of the words Max Continuous Thrust,
Mistrust in Management
Jonty is wrong
Can't be bothered with all the details, but just to say if you are above MCT the next limit applies - obvious really.
Having said that I agree with the previous posters that if terrain clearance is in doubt you keep the remaining engine firewalled. In the sim you should be given a realistic scenario, but nevertheless the same rules apply.
Having said that I agree with the previous posters that if terrain clearance is in doubt you keep the remaining engine firewalled. In the sim you should be given a realistic scenario, but nevertheless the same rules apply.
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Oldie but Goldie
From an old Nick Lappos post in Rotorheads:
"Arm,
You ask a good question. Let me try and explain it this way:
Imagine that each minute at TO power extracts one bean from a big jar of beans. One minute, one bean. If you stay at low cruise power, say 65% power, then five hours takes one bean out of the jar.
There is nothing unsafe about running at TO power, it is not "beyond limits". But if there are 10,000 beans in the jar, then you only get so much life from your engine, transmission and drive train.
We manufacturers set a 5 minute limit per takeoff as a way to remind you of that. Inside the factory walls, we imagine that you make about 2 1/2 takeoffs per hour (don't try a 1/2 takeoff, it should only be done by professionals!). We calculate that if one does 2 1/2 TO's per hour, and the rest in cruise then the power systems will last 3707 hours, and you will have performed 9200 takeoffs.
If you make more TO's, plan to overhaul sooner, if you make less, your engine will last a lot longer.
The numbers above are made up, but the idea that a takeoff is several times more damaging than a cruise hour is entirely true.
No thundering limit, where 6 minutes at TO power will end your life. Just a faster draining of those beans from the jar."
http://www.pprune.org/rotorheads/178...ml#post1942676
"Arm,
You ask a good question. Let me try and explain it this way:
Imagine that each minute at TO power extracts one bean from a big jar of beans. One minute, one bean. If you stay at low cruise power, say 65% power, then five hours takes one bean out of the jar.
There is nothing unsafe about running at TO power, it is not "beyond limits". But if there are 10,000 beans in the jar, then you only get so much life from your engine, transmission and drive train.
We manufacturers set a 5 minute limit per takeoff as a way to remind you of that. Inside the factory walls, we imagine that you make about 2 1/2 takeoffs per hour (don't try a 1/2 takeoff, it should only be done by professionals!). We calculate that if one does 2 1/2 TO's per hour, and the rest in cruise then the power systems will last 3707 hours, and you will have performed 9200 takeoffs.
If you make more TO's, plan to overhaul sooner, if you make less, your engine will last a lot longer.
The numbers above are made up, but the idea that a takeoff is several times more damaging than a cruise hour is entirely true.
No thundering limit, where 6 minutes at TO power will end your life. Just a faster draining of those beans from the jar."
http://www.pprune.org/rotorheads/178...ml#post1942676
I'll have to admit that I got a little lost in all the preceeding posts so I may not fully understand the original question.
given that there is a major annomaly in the operation of the aircraft e.g. an engine out the type certificate I read seems to put the time limit on the temperature limitation at 10 mins.
It defines the limitation based on EGT readings although the thermal damage if any is likely to be in the HPT.
Under most conditions all the thrust and aircraft performance that you need should not even approach the temp limitation. But for those conditions where it does approach or exceed the temp limitation your sense of the onset of serious damage will be a step change increase of EGT above the limit
just food for thought
given that there is a major annomaly in the operation of the aircraft e.g. an engine out the type certificate I read seems to put the time limit on the temperature limitation at 10 mins.
It defines the limitation based on EGT readings although the thermal damage if any is likely to be in the HPT.
Under most conditions all the thrust and aircraft performance that you need should not even approach the temp limitation. But for those conditions where it does approach or exceed the temp limitation your sense of the onset of serious damage will be a step change increase of EGT above the limit
just food for thought
HOWEVER, if you get to 5 or 10 mins and you feel you need to use it for a longer period of time then USE IT! Who gives a rats about the time limit. Take heed of this wizofoz, or you may need to reassess your priorities.
As such, I work for an airline that has engine out procedures that are designed to have the aircraft clean and clear of terrain inside the (for us 10 minute) limit for operation at greater than MCT.
If circumstances meant needing even TOGA power for longer to avoid terrain, of course I would do it- knowing I was exceeding a limit.
What YOU are suggesting is that the limit doesn't exist.
You're wrong.
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Jonty - you are incorrect
Checkboard (bless his AN socks) and Wizofoz are correct.
The limits on the engine are not managed by the engine certification data - they are managed via the Type Certificate Data - and there are occasionally differences.
Not all engines allow 5 minute AEO TO thrust to be used for 10 minutes OEI.
If the take-off is a derate - no thrust increase is permitted as the speeds are predicated on lower minimum control speeds
If the take-off is an assumed temperature flex takeoff, thrust may be increased to actual max TO thrust if required - noting that it is not necessary because terrain clearance should be assured if the RTOWs are correctly designed.
The sim scenario would seem to be designed to ensure that you understand the engine limits and the various thrust options for takeoff and continued flight. I'm thinking you need to start a clock at TO thrust application in any event - if you subsequently suffer a failure, any increase in thrust will be "money in the bank" for terrain clearance and MCT should normally be selected at 'aircraft clean' and inside the relevant time limit (unless you are conducting an approved procedure that permits you to accelerate at MCT with slats/flaps still deployed).
As an aside, the range of responses suggest that there are some Heads of Training and Checking who need to do their jobs better!!!
Stay Alive,
The limits on the engine are not managed by the engine certification data - they are managed via the Type Certificate Data - and there are occasionally differences.
Not all engines allow 5 minute AEO TO thrust to be used for 10 minutes OEI.
If the take-off is a derate - no thrust increase is permitted as the speeds are predicated on lower minimum control speeds
If the take-off is an assumed temperature flex takeoff, thrust may be increased to actual max TO thrust if required - noting that it is not necessary because terrain clearance should be assured if the RTOWs are correctly designed.
The sim scenario would seem to be designed to ensure that you understand the engine limits and the various thrust options for takeoff and continued flight. I'm thinking you need to start a clock at TO thrust application in any event - if you subsequently suffer a failure, any increase in thrust will be "money in the bank" for terrain clearance and MCT should normally be selected at 'aircraft clean' and inside the relevant time limit (unless you are conducting an approved procedure that permits you to accelerate at MCT with slats/flaps still deployed).
As an aside, the range of responses suggest that there are some Heads of Training and Checking who need to do their jobs better!!!
Stay Alive,
I will come at this another way to try and explain my point.
The engine has a limit of 5 mins at TOGA (850 deg C), at the 5 mins point I select CON (750 dec C) how long is it before I can reselect TOGA, and what is the time limit when I do? I could also ask how many times am I aloud to re-select TOGA on a single rotation. Is the 5 minutes a cumulative total or a total for a single application? None of this is mandated anywhere, we have to use our common sense.
According to the letter of the book, it would be perfectly acceptable to use TOGA for 5 mins then select CON for 30 seconds and then re-select TOGA for a further 5 min. However, we don't live in that world and in practise most of us would find this unacceptable abuse of the engine.
So what exactly is my point? My point is that there are very few absolutes in aviation. And with a little extra knowledge we can make educated decisions about such things. Hopefully in the full knowledge of what the limits are, and the likely consequences of operating beyond them. Its why we get paid the big bucks.
The engine has a limit of 5 mins at TOGA (850 deg C), at the 5 mins point I select CON (750 dec C) how long is it before I can reselect TOGA, and what is the time limit when I do? I could also ask how many times am I aloud to re-select TOGA on a single rotation. Is the 5 minutes a cumulative total or a total for a single application? None of this is mandated anywhere, we have to use our common sense.
According to the letter of the book, it would be perfectly acceptable to use TOGA for 5 mins then select CON for 30 seconds and then re-select TOGA for a further 5 min. However, we don't live in that world and in practise most of us would find this unacceptable abuse of the engine.
So what exactly is my point? My point is that there are very few absolutes in aviation. And with a little extra knowledge we can make educated decisions about such things. Hopefully in the full knowledge of what the limits are, and the likely consequences of operating beyond them. Its why we get paid the big bucks.
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Jonty,
Our airline (mixed fleet) contacted the various engine manufacturers about this. the 5/10 minute rule is a THRUST limit and not a time limit. So regardless if the EGT achieved is less than the maximum you MUST select a lower THRUST setting - unless terrain is a factor then all bets are off.
Our airline (mixed fleet) contacted the various engine manufacturers about this. the 5/10 minute rule is a THRUST limit and not a time limit. So regardless if the EGT achieved is less than the maximum you MUST select a lower THRUST setting - unless terrain is a factor then all bets are off.