B757 Assumed temperature T/O thrust time limit?
Thread Starter
Join Date: Feb 2001
Location: UK
Posts: 85
Likes: 0
Received 0 Likes
on
0 Posts
B757 Assumed temperature T/O thrust time limit?
Hi all
I have a dilemma, I am about to go in the sim for an apparently quite challenging profile and need to find some info on the above. I know that the B757 (RB211-535-E4) has a max TOGA time limit of 5 mins but I hear rumours that this doesn't apply if you have an assumed temperature set. now this to me is common sense as with an assumed temp you will be taking off with less than max thrust BUT where is it written that Assumed temp cancels the TOGA time limit? I'll try to put this in context:
A/c takes off full thrust (1.72 EPR) and loses an engine, the book says that you are limited to 5 mins so in a limiting place such as Chambery or Geneva with a long emergency turn you're going to be in a situation where you need to reduce thrust to MCT earlier than your normal profile would have you do.
so the alternative
A/c takes off at say 39 Degrees Assumed temp and gets lets say 1.68EPR. Same thing happens engine goes bang and you have a long drawn out emergency turn procedure. Notwithstanding knowing all the percentages of the MCT performance bracket of the engine where do I now find myself when I hit the magical 5 mins?
I know from experience in the box that often if you have taken of at a high assumed temp (+54) then you often end up increasing power on the live engine hence I would suggest in this case reducing thrust is not really an issue but the point remains where is it written that when using an assumed temp (no matter what that might be) means we can dispense with the 5 minute limit and happily follow the standard EFATO profile no matter how long the emergency turn.
Your help is greatly appreciated
I have a dilemma, I am about to go in the sim for an apparently quite challenging profile and need to find some info on the above. I know that the B757 (RB211-535-E4) has a max TOGA time limit of 5 mins but I hear rumours that this doesn't apply if you have an assumed temperature set. now this to me is common sense as with an assumed temp you will be taking off with less than max thrust BUT where is it written that Assumed temp cancels the TOGA time limit? I'll try to put this in context:
A/c takes off full thrust (1.72 EPR) and loses an engine, the book says that you are limited to 5 mins so in a limiting place such as Chambery or Geneva with a long emergency turn you're going to be in a situation where you need to reduce thrust to MCT earlier than your normal profile would have you do.
so the alternative
A/c takes off at say 39 Degrees Assumed temp and gets lets say 1.68EPR. Same thing happens engine goes bang and you have a long drawn out emergency turn procedure. Notwithstanding knowing all the percentages of the MCT performance bracket of the engine where do I now find myself when I hit the magical 5 mins?
I know from experience in the box that often if you have taken of at a high assumed temp (+54) then you often end up increasing power on the live engine hence I would suggest in this case reducing thrust is not really an issue but the point remains where is it written that when using an assumed temp (no matter what that might be) means we can dispense with the 5 minute limit and happily follow the standard EFATO profile no matter how long the emergency turn.
Your help is greatly appreciated
Join Date: Sep 1999
Location: uk
Posts: 139
Likes: 0
Received 0 Likes
on
0 Posts
Simple answer is that once your engine goes bang it is normal procedure to apply full power immediately on the remaining engine as this is what the single engine performance is based on. After the 5 mins is up you would need to assess the situation. If critical continue at full power or if not select max cont power.
You would never normally require more than 5 mins at full power. The only place I know of in Europe is Innsbruk. As we operate into this airfield our 757's E4 engines have been upgraded to 10mins at full power.
You would never normally require more than 5 mins at full power. The only place I know of in Europe is Innsbruk. As we operate into this airfield our 757's E4 engines have been upgraded to 10mins at full power.
Thread Starter
Join Date: Feb 2001
Location: UK
Posts: 85
Likes: 0
Received 0 Likes
on
0 Posts
Waldo
Thanks for your quick response,
This is interesting as our training says that the perf we use is predicated at remaining at assumed temp thrust with the engine out thus you DON'T apply full power or rather you don't HAVE to.
The understanding is that you are taking a reduction in thrust to an assumed temp that will allow the remaining engine to lift the given weight taking into account all the usual perf stuff like obstacles and field length etc. Under your system as you say there is no question as you have full thrust but we remain at the assumed temp thrust and thus the question remains.... when do I reduce if at all?
Thanks for your quick response,
This is interesting as our training says that the perf we use is predicated at remaining at assumed temp thrust with the engine out thus you DON'T apply full power or rather you don't HAVE to.
The understanding is that you are taking a reduction in thrust to an assumed temp that will allow the remaining engine to lift the given weight taking into account all the usual perf stuff like obstacles and field length etc. Under your system as you say there is no question as you have full thrust but we remain at the assumed temp thrust and thus the question remains.... when do I reduce if at all?
Join Date: May 2006
Location: NL
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
Waldo is not correct. The performance is based on the assumed calculated temp. This sould clear all obstacles. You can however always select full thrust if desired, but not necessary.
i,am not sure for 757 but on (at least our) 737 we have a 10min thrust limit once SE If you use full thrust then it's only alowed for max 10 minutes. so our normal ops is after cleanup to selct Max Cont. Thrust (MCT) to continue the climb.
Only in special cases you could run into the 10min max. When making a SE-go-around with a very high accelaration segment you could run into the time limit.
i,am not sure for 757 but on (at least our) 737 we have a 10min thrust limit once SE If you use full thrust then it's only alowed for max 10 minutes. so our normal ops is after cleanup to selct Max Cont. Thrust (MCT) to continue the climb.
Only in special cases you could run into the 10min max. When making a SE-go-around with a very high accelaration segment you could run into the time limit.
Thread Starter
Join Date: Feb 2001
Location: UK
Posts: 85
Likes: 0
Received 0 Likes
on
0 Posts
Lord Spandex Masher
Yes I agree in the real world I would indeed use everything I have and be done with it but in the virtual world a TRE is very likely to simply fail the other engine at the 5 minute point making for a rather unpleasant debrief hence the question so when that point arrives I have something to use in my defense if I was using assumed temp.
Punk
You are talking about the same problem i.e. FULL thrust has a 10 min (737) limit. I am talking about the assumed temperature scenario where you are already derated by virtue of the assumed temp method below MAX TOGA so do you need to worry about the 5 mins? it is a grey area I fear between the TOGA limit and the MCT limit, if you are between the 2 limits when using assumed temp then what is your time limit?
Yes I agree in the real world I would indeed use everything I have and be done with it but in the virtual world a TRE is very likely to simply fail the other engine at the 5 minute point making for a rather unpleasant debrief hence the question so when that point arrives I have something to use in my defense if I was using assumed temp.
Punk
You are talking about the same problem i.e. FULL thrust has a 10 min (737) limit. I am talking about the assumed temperature scenario where you are already derated by virtue of the assumed temp method below MAX TOGA so do you need to worry about the 5 mins? it is a grey area I fear between the TOGA limit and the MCT limit, if you are between the 2 limits when using assumed temp then what is your time limit?
You don't have to take full power following an EFATO - see how the ac performs. However, pre briefing (and then doing) 'full power on the live engine please' is one less decision to have to make at a time of great stress!
Join Date: May 2006
Location: NL
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
Yes, good question
If you are above MCT i would say, safety wise, the time limit for max thrust (5/10min) because you are over your continuous setting.
In practice often when setting MCT after an engine failure in our operation we can ADD thrust, since selected temp often reduced the thrust to below the MCT setting.
If you are above MCT i would say, safety wise, the time limit for max thrust (5/10min) because you are over your continuous setting.
In practice often when setting MCT after an engine failure in our operation we can ADD thrust, since selected temp often reduced the thrust to below the MCT setting.
Join Date: Nov 1999
Posts: 2,312
Likes: 0
Received 0 Likes
on
0 Posts
Max T/O thrust is limited to 5 minutes, unless an engine fails in which case it is extended to 10 minutes. Normal 2 engine maximum thrust can be extended to 10 minutes by certification. This is often done for operations from airports such as Innsbruck where more than 5 minutes at fully rated thrust may be required (although in practice it usually isn't.) Assumed temperature is used to de-rate the take off thrust, so the point is generally redundant if you are not using maximum rated take off thrust.
Note that N1, N2 and N3 pointer and counter displays are inhibited from turning white to amber, if they enter the (near limit) amber band during take off or go around (TOGA) for 5 minutes after the band is first entered. However if engine failure occurs in that 5 minute period, the inhibit period increases to 10 minutes.
certificate data docs.
Note that N1, N2 and N3 pointer and counter displays are inhibited from turning white to amber, if they enter the (near limit) amber band during take off or go around (TOGA) for 5 minutes after the band is first entered. However if engine failure occurs in that 5 minute period, the inhibit period increases to 10 minutes.
certificate data docs.
Join Date: Jun 2010
Location: Brisbane, Australia
Posts: 304
Likes: 0
Received 0 Likes
on
0 Posts
Yes, I agree with 'punk2039' here, any thrust setting in excess of MCT will be subject to the appropriate time limit, it doesn't have to be pushed all the way up to incur the limit time.
EW73
EW73
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,497
Likes: 0
Received 0 Likes
on
0 Posts
Yup, if you do not know if you are above or below MCT, just set it at the time limit. If you have reduced take off thrust in many cases you will add thrust at that point, not reduce it. Dunno if the 757 has fixed derates used together with ATM, in that case it is actually absolutely normal to increase thrust with setting MCT.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
Just a word from an engine guy: I'm fully aware of the 5 min. TO limit, and I also know that an extension to 10 min. (authorized in some jurisdictions) is merely a paperwork exercise (maybe with some shekels crossing the palm) - no spanners ever touch the engine.
And in my career doing performance tests on engines, we started with a 5 min. warmup at MCT, then pushed up to rated TO for 5 min., backed down a few rpm for another 5, then an alternate TO rating for another 5, etc. for a total of 30 to 45 minutes ABOVE MCT. I've done this DOZENS of times, never any hint of an incipient failure. (I shudder to think of the JetA I've burned...)
My message to pilots: Find out what your examiners expect you to know, but when one's churning and one's burning, FLY THE AIRPLANE and don't worry about that other donk!
And in my career doing performance tests on engines, we started with a 5 min. warmup at MCT, then pushed up to rated TO for 5 min., backed down a few rpm for another 5, then an alternate TO rating for another 5, etc. for a total of 30 to 45 minutes ABOVE MCT. I've done this DOZENS of times, never any hint of an incipient failure. (I shudder to think of the JetA I've burned...)
My message to pilots: Find out what your examiners expect you to know, but when one's churning and one's burning, FLY THE AIRPLANE and don't worry about that other donk!
Its a fairly simple answer. If you took off with an assumed temp set (thrust derate) then you are not at TOGA and the TOGA limit does not apply. If you subsequently set TOGA then the clock starts running.
If you need TOGA for longer than the limit, then use it. There is no point in reducing thrust and hitting a mountain. However the time limit should be taken into account by the company when producing the performance profile for the aircraft.
If you need TOGA for longer than the limit, then use it. There is no point in reducing thrust and hitting a mountain. However the time limit should be taken into account by the company when producing the performance profile for the aircraft.
Originally Posted by Jonty
If you took off with an assumed temp set (thrust derate) then you are not at TOGA and the TOGA limit does not apply. If you subsequently set TOGA then the clock starts running.
At the time limit, simply call "Set MCT" to the other pilot - if they increase the power to do that, fine, if they decrease it - then you have just passed (that portion) of your check
Er No, its a TOGA limit. The book says "the time limited at TOGA thrust" it doesn't say "the time limited above MCT"
Just to add to this, its actually an EGT limit. 850 deg C for 5 min. SO you could argue if your at 849 deg C the time limit does not apply.
Why I still have the books I don't know, I haven't flown the thing for 5 years!
Just to add to this, its actually an EGT limit. 850 deg C for 5 min. SO you could argue if your at 849 deg C the time limit does not apply.
Why I still have the books I don't know, I haven't flown the thing for 5 years!
Last edited by Jonty; 14th Feb 2012 at 08:51.
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Hi Jonty,
Take Off / GA thrust is what you set to do one of those procedures - it is doing what it says on the tin. You are being checked in the sim to apply the approved procedures within the time limits for your engine settings.
Are you really serious?
Take Off / GA thrust is what you set to do one of those procedures - it is doing what it says on the tin. You are being checked in the sim to apply the approved procedures within the time limits for your engine settings.
Just to add to this, its actually an EGT limit. 850 deg C for 5 min. SO you could argue if your at 849 deg C the time limit does not apply.
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Hi Jonty,
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?
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?