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!

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!

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

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