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.

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.

HI,

Here a quote from Captain Lim website (He is/was B 777 pilot):
"

Here a quote from Airbus article (smart cockpit):
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:
.
Does it mean pilot can use the bump on the operative engine in case of engine failure?

Feedback appreciated
Regards

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.

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.

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.)

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.

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.

cfm thrust ratings
 

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:

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 ...

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

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

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:

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.

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.

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 ...