Engine derates, thrust lever range

[QuEsT147]

Greetings to all

I have another question, maybe answer is obvious, but jus t want to make sure.

Assume you have for example 200 kN engine, full rate. In this case, with thrust lever in full aft position you have 0 kN thrust and in full forward position you have 200 kN thrust, to be simple.

Now you derate the engine so the new max thrust is for example 180 kN. In this case, do you also have the new max 180 kN thrust with TL in full forward position OR 180 kN TL position is somewhere in between full aft and full forward and you have to pay attention to not overboost the engine?

Thanks for enlightening it for me :)
Rgds

QuEsT147

[Old Smokey]

You don't mention the aircraft or engine type, but on the B777 (all variants) FULL Thrust Lever provides Maximum Takeoff Thrust irrespective of any de-rates or reduced thrust that may have been selected.

Balls to the wall - You got it all!:ok:

Regards,

Old Smokey

[QuEsT147]

Old Smokey

Thanks for your answer. Regarding the type, I mean B737. So from your answer, TL position for the max derated thrust IS between full aft and full forward, do I understand correctly?

Rgds
QuEsT147

[Old Smokey]

QuEsT147,

What you say is absolutely correct for a B777 (for which I answered), it's exactly 20 years since I last flew a B737 (-300), so I cannot answer with any certainty.

It would SEEM so, Boeing logic is pretty universal across it's types, I think better to wait for a REAL B737 pilot to reply!:ok:

Regards,

Old Smokey

[Intruder]

For the GE CF6 engines, full forward throttle lever = full thurst. In the new CF6-80 with electronic engine control, that is limited by the EEC for current conditions. For the old CF6-50 with mehcanical fuel control, full forward may give an overspeed or overtemp or overthrust.

In either case, using the autothrottle with a fixed derate will move the throttles to a position aft of full forward. More thrust is available by manually pushing the levers to the stops.

[bucket_and_spade]

And, just to be pedantic, you'd still have idle thrust at full aft thrust lever position not zero thrust as per your original post!

[Sir Richard]

If the engine has been de-rated in the shop rather than as a t/o derate, then the 180Kn thrust will be achieved at full forward thrust lever.

When flying with a mix of engines (RR744) it would be possible to have G H or T cores, but all would be rated to the lowest power output. The only noticeable differences would be in the EGT and Fuel Flow.

[QuEsT147]

BaS
Of course, I am aware of this, just wanted to make things clear :)

Intruder, Sir Richard
Thanks for your replies... So it seems that when "software (FMC)" derated, new max thrust TL position is between full aft and full forward, and when "hardware" derated, new max thrust TL position is full forward, is it right?

Thanks all for your informative inputs, this forum is great:)

Rgds
QuEsT147

[Intruder]

So it seems that when "software (FMC)" derated, new max thrust TL position is between full aft and full forward, and when "hardware" derated, new max thrust TL position is full forward, is it right?
As long as you include derates "firmware" encoded in the EEC as "hardware" derates, you are essentially correct. The main physical difference between a CF6-80-B1 and CF6-80-B5 engine is an EEC module that limits thrust. So, it is "software" limited, but not in the FMC.

[Denti]

I guess what he means is the possibility to change the thrust rating with a push of a button while on the right FMC page as is the case for all 737 models from the -300 on (no execute needed, it is active immediately). Most other boeing models seem to have the ability of fixed derates as well, so that is not a 737 only thing.

The 737 works exactly as Old Smoky describes for its big brother, however on the classics you do not have any protection and can overboost the engine when firewalling the thrust levers. On the NG the EEC protects you against that. However when derating and using performance figures for a derate you have to be aware that firewalling might put you into an uncontrollable state as the VMCg and VMCa are different for each derate setting.

[barit1]

CF6-50 (& -6), as well as similar vintage R-R and PW engines, are "part throttle" engines at takeoff. All would be more or less overboosted if run at the max stop. The OEM may (& probably does) require some sort of inspection before the next flight.

In most cases such an overboost will be fairly minor, but still is a no-no.

And thank you Denti for reminding us of Vmga & Vmcg limitations. Flying sideways is not a good thing.

[AeroTech]

Hi,

When I read the posts above, I am confused. Both B 777 and B 737 NG are fitted with ECC, yet you get full rated thrust for B 777 and derated thrust for B 737 NG when you firewall the thrust levers (according to some posts above)?

If I am not mistaken I read a certain Airbus article (smartcockpit website) that states: pilot cannot recover TOGO. Don’t quote me because I don’t know the exact context where this note was mentioned, all I know is the subject deals with derated engine.

I don’t know the veracity of the following quote but here a link: Assumed Temperature Thrust Reduction (http://www.b737.org.uk/assumedtemp.htm)
A de-rate is a semi-permanent engine fix, used to reduce the maximum thrust available; for instance down to 20k from 22k on -3/700's. It is also used to equalise the thrust where B2 & C1 engines are mixed on the same airframe. When an engine is de-rated, the full (un-de-rated) thrust is no longer available because this would require changes to the EEC, HMU, fuel pump, engine ID plug and the loadable software; non of which can be done by the pilot in-flight.
A temporary form of de-rating known as a "T/O de-rate" is accessible through the FMC on TAKEOFF REF 2/2 or N1 LIMIT (NG's) but this is prohibited by some operators. The T/O de-rates (TO-1 & TO-2) can be 10 to 20%. It follows that an engine may be de-rated and also be using reduced thrust in which case you could be taking off at Full power -20% -25% = 60% of the full power of the engine - scary thought! Note that a T/O de-rate can overridden by firewalling the thrust levers

Feedback appreciated
Regards

[barit1]

It follows that an engine may be de-rated and also be using reduced thrust in which case you could be taking off at Full power -20% -25% = 60% of the full power of the engine - scary thought!

Not scary if you contemplate that such a takeoff is likely to be on a very very long r/w, no departure obstacles, at a low gross weight. Why not choose a thrust appropriate for the situation?

Note that a T/O de-rate can overridden by firewalling the thrust levers

Now that IS scary! Override a derate - and you're operating beyond the AFM limitations for that derate chapter. You've become a test pilot, and likely to find yourself below Vmca (or Vmcg!).

I'd NEVER try that OEI, unless I was WAY above Vmca.

[Intruder]

YOU are the one that is scary if you would try a TO with derate plus an assumed temp reduction!

Indeed, the charts do not allow for adding thrust after an engine failure on TO when using a fixed derate. However, they DO allow for a safe TO without that addition.

Whose AFM/PHB/FCOM allows the use of simultaneous derate + reduction?

[FlightDetent]

I believe that the large Airbuses AFM allows exactly that (and wait to be corrected). The performance figures are then calculated accordingly. The only scary thing to put you outside calculated limit is to override the derate which, again my understanding, is technically undoable.

FD (the un-real)

[Denti]

When I read the posts above, I am confused. Both B 777 and B 737 NG are fitted with ECC, yet you get full rated thrust for B 777 and derated thrust for B 737 NG when you firewall the thrust levers (according to some posts above)?

No, they behave the same. Firewalling gives you full rated thrust on the 737 NG (the classic can give more than full rated thrust overboosting the engine in the process), which is a very unwise thing to do when using a derate.

@Intruder, the 737 NG is certified for using a combination of derate and assumed temperature as factory standard, the 737 classic need an AFM supplement but can be certified for the same as well. We use it on our 737s every single take off. Yes, it can be quite weird to take off with a N1 of 76% (derate 2 18k and over 60° assumed on the -700), but you get figures like that only on 4km runways with a low obstacle situation.

As barit says, using more than calculated thrust in the one engine out case is something not to do unless you checked the full rated VMCg/a and are above those speeds. Something you usually do not have the time to do during a V1 cut. Therefore our SOP is to just leave the thrust where it is until clean up is completed as the performance is calculated for the OEI case anyway.

[barit1]

Whose AFM/PHB/FCOM allows the use of simultaneous derate + reduction?

The ones I am familiar with go back 30 years - DC-10-30, 747-200, A300B4. The practice has been standard AT LEAST that long, and continues today.

[Intruder]

Not allowed on our 747s -- Classic or -400. In fact, the max allowed reduction is 25%.

I don't know why you would use more than a 25% reduction in any case. At that thrust level there is no more "savings" from "reduced engine wear," because the temps and pressures are so far below the design limits. All you do is eat up runway and reduce your safety margins.

[barit1]

Intruder:

Does your co. version of the AFM include a derate chapter? IIRC a 10% derate chapter is typical - but I suspect Boeing does not include it in the basic price of the a/c. You have to pay extra for it.

But this begs the question - What is your SOP for contaminated runway? You cannot use flex (ATM) reduction, per FAA order.

[Pugilistic Animus]

I knew that someone would eventually override the Derate in this thread it ALWAYS happens:\

PA

[Intruder]

Does your co. version of the AFM include a derate chapter? IIRC a 10% derate chapter is typical - but I suspect Boeing does not include it in the basic price of the a/c. You have to pay extra for it.

But this begs the question - What is your SOP for contaminated runway? You cannot use flex (ATM) reduction, per FAA order.
Yes, we have charts for Derate 1 and Derate 2. The Derate values vary with aircraft and engine, to 20% max. However, we have switched to computed thrust values using Reduced Thrust for normal operations. All Reduced Thrust calculations use full TO thrust as baseline, and are limited to 25%.

Fixed derates are allowed on contaminated runways.

[barit1]

OK, you have your bases covered, and evidently your company chooses to simplify things with the protocol you describe. This has, I guess, the advantage of forcing the highest Vmcg and Vmca so you don't have that to worry about.

But the fact is, you can apply reduced thrust to any certified rating, including Derates 1 & 2.

There's a bit of history behind this: Say an early model airplane is delivered with engines rated A, and later an upgrade to B is offered. The A rating is permitted to use flex thrust down to a 25% reduction. When B engines are installed, the A rating is still valid, including its 25% reduction. This has occurred many times over the years.

EDIT: My upper management once embarked on some "housecleaning", and planned to remove the old engine A rating from the type certificate data sheet. We flight ops people saw the folly in this, especially the effect on contaminated r/w ops. I wrote the letter that got this plan buried.

[AeroTech]

HI,

No, they behave the same. Firewalling gives you full rated thrust on the 737 NG (the classic can give more than full rated thrust overboosting the engine in the process), which is a very unwise thing to do when using a derate.

Here a quote from Captain Lim website (He is/was B 777 pilot):
How is an assumed temperature take-off different from a "derated" take off? A de-rated engine is a semi-permanent engine fix used to reduce the maximum thrust available. A temporary form of de-rating is known as a "T/O de-rate"

Here a quote from Airbus article (smart cockpit):
Derated Takeoff procedure: pilot cannot recover TOGA.

Zeke (I guess he is Airbus pilot) said in another forum that there are 2 kinds of derate: Hard derate (similar to semi-parmanent) and soft derate (similar to temporary derate, known as “T/O derate”).

My point to post these quotes is to indicate that before stating that firewalling the thrust levers gives the full rated thrust we should mention if it is semi-parmanent or temporary derate.

Another quote from Airbus article regarding Bump activation:
The bump is activated by two guarded pushbuttons, placed on the thrust levers on the A320 Family and on the external thrust levers on the A340.
It can be used with all engines operating and remains active in case of one engine failure.
Does it mean pilot can use the bump on the operative engine in case of engine failure?

Feedback appreciated
Regards

[Denti]

I guess airbus does it differently and "protects" the pilots from violating the max derated thrust, probably to protect them from busting VMCg/a. Boeing doesn't, you can allways get max thrust or even more in the case of non-FADEC engines.

As pilots we usually talk about what we can do, and the derates we can do are temporary take off derates, not permanent ones. The latter ones probably need a bit more work than just pushing a line select key on the N1 page.

Bump sounds weird, is that something like extra take off thrust above the normal engine rating? I knew those airbuses have performance problems from our airbus fleet, but i wasn't aware that it is that bad.

[Intruder]

With an engine failure at or above V1, TO performance for a fixed derate is based on NOT using any added thrust -- use of added asymmetrical thrust may take you out of the protected VMCg. With an Assumed Temperature thrust reduction, additional thrust MAY be used.

Specific airline procedures may dictate NO additional thrust with reduced thrust also.

Know your airplane. Know your procedures. Know why the procedures are what they are.

[barit1]

Thrust "bumps" may be negotiated for specific routes (e.g. MEX > Europe) - this is usually an extra few % at a high elevation airport. It's specific to that airline, and some extra $$$ changes hands to account for extra wear & tear (warranty costs) on the engines. (Probably the wheels & tires too, if higher GS is used.)

[john_tullamarine]

With an engine failure at or above V1, TO performance for a fixed derate is based on NOT using any added thrust -- use of added asymmetrical thrust may take you out of the protected VMCg. With an Assumed Temperature thrust reduction, additional thrust MAY be used.

Points of note -

(a) neither derate nor FLEX require any pilot adjustment of thrust in the event of a failure ie, the normal RTOW calcs are predicated on the thrust level set at the start of the takeoff.

(b) FLEX will/derate may tolerate an increase in thrust on the operating engine - caveat - do it SLOWLY as there is a risk of a thrust overswing depending on the engine control systems. In any case, at a critical stage of flight, the handling pilot doesn't need the additional complication of having to dance a jig on the pedals to keep the aeroplane more or less straight while the lever is being pushed up.

(c) Vmcg/a should only be a problem for a very lightweight takeoff at, or near, min speed schedule. One of the saving graces is that the light aircraft typically will be accelerating rapidly and, by the time the pilot increases thrust, the actual IAS will be somewhat higher than what the takeoff was predicated on.

(d) It still is presumed that any adjustments by the pilot will be such that the rated (or derated) thrust level is not exceeded.

[Intruder]

(c) Vmcg/a should only be a problem for a very lightweight takeoff at, or near, min speed schedule. One of the saving graces is that the light aircraft typically will be accelerating rapidly and, by the time the pilot increases thrust, the actual IAS will be somewhat higher than what the takeoff was predicated on.
We do an exercise in initial training and every 2 years in recurrent that illustrates the effects of Derates on VMCg. The scenario used is a contaminated runway. The difference in VMCg between Full TO and TO2 thrust is significant. The urge to add thrust after an engine failure would likely result in catastrophe, if followed.

[godu]

whats apparent is that say 27k engine is limited by the EEC, but at full thrust say at full take off setting, you can still move the TL beyond and get more than 27 k. If on derates you can still do this but you are Vmcg critical and can lose direction on eng fail. But an assumed temp derate or full rate lets you open the TL not making you Vmcg critical.:ok::ok:

[john_tullamarine]

But an assumed temp derate or full rate lets you open the TL not making you Vmcg critical

Just make sure you have some knowledge of your engine's acceleration characteristics ..

(a) will the engine driven yaw rate present a control problem ?

(b) will there be a short-lived thrust overswing .. ditto ?

If you must up the thrust, consider doing it slowly ...

[barit1]

If you must up the thrust, consider doing it slowly ...

I do like the way you put it, JT...

[godu]

Firstly, are you telling me to know about engine accl or that u say I dont know about it at all? Any way, just to remind you, the last 50% of jet thrust is controlled by the last 20% of the engine RPM. When u are performance restricted by Vmcg on a fixed derate, the book says not to firewall the live engine for an engine failure at V1. This is because your controllability has been factored to this lower speed, and getoff the ground with enough control.( Sure ,u've seen this in the sim).But on an assumed temp T/o with full or derate u need to move up the TL as ur present thrust is way low and the Vmcg is not restricting u.:ok:

[Denti]

But on an assumed temp T/o with full or derate u need to move up the TL as ur present thrust is way low and the Vmcg is not restricting u.

Actually, no. Performance for ATM is calculated for the OEI case anyway, so there is no need to increase thrust. It would be easy to do so for the full rated ATM case, however for the derate ATM case you do not know where the max thrust for that derate is and you might bust it if you just push the thrust levers forward. Leave them alone, it is all safe if you used correct performance data.

[barit1]

godu - NO, if you've done your sums right for the ATM TO, the OEI case IS ALREADY COVERED and you'll only complicate the matter - perhaps falling below Vmca/Vmcg - by increasing thrust.

In fact, an ATM takeoff already provides more margin than a true hot-day rated takeoff.

[john_tullamarine]

the last 50% of jet thrust is controlled by the last 20% of the engine RPM

wherein lies the problem .. it all happens very quickly

or that u say I dont know about it at all?

comment was generic .. certainly not referring to your specific knowledge base

perhaps falling below Vmca/Vmcg - by increasing thrust.

if the takeoff speed schedule is low (typically associated with a very low weight takeoff - eg positioning flight), a rapid ramping up of thrust during the intial takeoff sequence may result in a thrust overswing (depends on the engine characteristics, naturally enough) and a sufficient increase in the real world Vmc to provide undesirable results.

The better routine strategy is to set the thrust at the start of the takeoff roll and leave it for routine failure situations. Perhaps you're a much better manipulator than I .. I always found I had quite enough workload without playing about with the throttle setting as well ...