Full T/O power on take off!
 

I know this might have been discussed before. But assume that one is taking off with assumed AND derated take off power on the 777. On take off roll,when and how would one get full flat rated take off thrust...if at all!
Thanks all for the session in advance..
:cool:

First, is the 777 certified to do assumed temp + derate for T/O? Our 747s are not.

Second, AFAIK, pushing the thrust levers full forward will give full thrust.

.1. By Pushing the Thrust Levers Fully Forward, OR

.2. By pressing the TOGA switches a second time.

That will do it :ok:

Regards,

Old Smokey

Smokey....with due respect..
Both the procedures you mentioned will give me max derated thrust. Say I have 2 standard derates(10% and 20%)and I take off using the 20% derate with an assumed temp. THEN if i hit TOGA a second time OR push the TL's full forward I should get max(ie no assumed temp)of the 20% derate.
But how do i get MAX un-derated power from a derated assumed temp take off. Or is it not possible...
I thought it was possible,but required pushing the TOGA at a certain point in the T/O roll...
But correct me please..

Just a guess, but disconnect the autothrottle (you can, you know) and push the thrust levers forward.

I think Old Smokey is correct.

I am not familiar with the 777, but 737, and I ""assume" similarities.
Your Derate and assumed temp is set for your departure runway. Say you derate.
When you go land a bit later somewhere else, and make a go-around, you might need full go-around trust due to weight and obstacles. So full go around trust is available here by pushing TOGA twice. This trust can not be a function of the derate you set at your departure airport, right?
So push TOGA again after TOGA is set for take off, gives you full rated trust.
It might give you even so much power that , in case of an engine failure, you cannot maintain directional control, due to the fact that your speeds were calculated for the Derated trust,and now you have increased VMCG and VMCA.
The FCTM warns you for this in the B737.

IIRC a second push on the toga buttons on 737 (NG at least) has zero effect on the take off roll. As far as the triple goes I don't know for sure but I'd be surprised to see the thrust levers firewalled and you not getting max thrust, doesn't seem very Boeing...

Smokey,

On the take-off roll, above 80kts, all that does is disarm LNAV and VNAV- you need to advance the thrust levers manually to get any more grunt.

King,

Can't answer your question as I've never flown an A/C that HAD T/O derate- but, would cancelling it through the FMC work?

Cut and pasted from the 737 NG systems manual.

The FMC will command the required thrust based on the temp. input used and the T/L's will be positioned accordingly. If you then need max. power for instance, stuffing the levers to the stop will give you max. power available for the day based on local temperature.
Modern engines are not like the old 'part throttle' motors that would attempt to give whatever it could only limiting RPM by the speeder spring and bobweights in the JFC.

If you then need max. power for instance, stuffing the levers to the stop will give you max. power available for the day based on local temperature.

However, one probably ought not to do that unless

(a) one, preflight, had checked the max thrust min speed schedule

(b) one was operating to a speed schedule somewhat in excess of (a)

(c) if (a) and (b) are satisfied, one advanced the throttles steadily but not (too) rapidly. Dynamic handling problems in an already high stress/workload situation might just be the straw which breaks the camel's back.

I have been involved with one accident investigation where the above, in analogy, was not observed and the outcome, shall we say, was somewhat less than ideal.

In retrospect, after posting, I was afraid that the 'other' considerations of a second press of the TOGA switches was going to raise it's head. I was thinking of the airborne engine failure case (comes from doing too much work on engine failure after Takeoff cases), rather than the 'On the grounf all engines operating case'. I should have read the original post more carefully:)

To qualify my 'second press of TOGA' remarks, the first is the application of Takeoff thrust at the commencement of Takeoff, the second is the next one. There is a significant difference between the on ground and in flight cases.

Wizofoz, you are absolutely correct in stating "On the take-off roll, above 80kts, all that does is disarm LNAV and VNAV- you need to advance the thrust levers manually to get any more grunt. Yes, full Thrust lever position ONLY will give you FULL Un-Derated Takeoff thrust.

King on a Wing, with respect, for the in flight case, you're incorrect, but I wish that you were correct!

.1. On the ground, pushing the Thrust Levers to the fire-wall will give you Maximum Takeoff Thrust, and

.2. In flight, following engine failure, pressing the TOGA switches OR pushing the Thrust Levers to the fire-wall will give you Maximum Takeoff Thrust. Pressing the TOGA switches removes the derates, and this is where I wish you were correct...... more on this -

V1, Vr and V2 are based upon Vmcg and Vmca for the Derated Thrust. The problem arises after engine failure that if, for example the V speeds were based upon TO-2 (20% De-Rate), full Takeoff thrust might put you into a severe and unrecoverable directional control situation, yet, some people will do it. I wish you were correct in stating that pressing TOGA 'only' removed the Assumed Temp and gave you full De-Rated thrust, that could be highly desirable, but it is not so, you get the full works. The only way to obtain the De-Rated thrust is to obtain the value from the FMC, and manually push the Thrust Levers to that value.

In our company we were concerned that on short flights where TO-2 was used with a large Assumed Temperature, pilots might press TOGA to obtain Full Thrust, and lose control. Our solution, as imperfect as it may be, was to determine the minimum weight at which the V Speeds provided VMC protection, and to NOT advance to TOGA following engine failure below those weights. (It's a low weight Takeoff problem). NO, I'm not going to quote the weights as there are numerous varients out there, so look up the numbers for your own Aircraft / Engine combination.

Next time, I promise to thoroughly read the OP's text fully, as I've started an inadvertant thread drift. Sorry about that.:uhoh:

Regards,

Old Smokey

Is it me, or, does anyone else get the impression that some of the questions that are being asked within this forum are somewhat ridiculous?

Why would someone ask 'how' to gain maximum thrust from any given engine? I would have thought that any self respecting aviator would know how to do that; either via the FMS or those levers in front of you!

Jeez!

Maybe some of the posters just want to get to your level of knowledge.

Young fella inquiry
 

So, if you were to apply full underated thrust to an engine during a go around or EFATO, is the max thrust limited:

1) by the assumed temp entered in the FMS for derated thrust T/O or,

2) is it limited by max ITT or,

3) is it limited by maximum rated thrust regardless of ITT
(doubt its this one)



rocket

we were concerned that on short flights where TO-2 was used with a large Assumed Temperature, pilots might press TOGA to obtain Full Thrust, and lose control

.. an extremely valid point.

Which is why, if the operator is going to permit, and pilots are intending to do .. the increase throttle thing ... the sim program should look at critical speed/thrust failures lest the real event create more excitement than the typical pilot might deem appropriate.

Around 10 years ago, I was involved with a 732 contract training task where the operator had an aerodrome from which a routine positioning flight was made at very light weight .. and used a min weight/speed schedule. However, just about all the remaining flying was done at high V2 overspeed speed schedules. You guessed it - their sim program ignored the odd man out aerodrome.

For interest, I had several crews (who volunteered) to have a looksee at the min speed situation (not even involving increasing throttle settings - this was for set throttle and leave it alone). As I recall, in every case, the aircraft (sim) departed from controlled flight. All the pilots were quite able to get on top of the problem with a couple of practice runs.

However, the point was made very clearly - don't do your first time practice on the line with a real failure ....


1) by the assumed temp entered in the FMS for derated thrust T/O or
2) is it limited by max ITT or,
3) is it limited by maximum rated thrust regardless of ITT

(1) flex should never be limiting - if you really want to do so you can advance to the derate setting

(2) probably won't be limiting for a derated takeoff

(3) is the answer we are looking at providing "max thrust" refers to the derate level. For a derated takeoff, the rated thrust is the derate value, not the thrust rating for nil derate. Derate is analogous to changing engines, flex is just operating at part throttle.

Caveat - ITT limit is always limiting if ITT were to get to that temperature.

i think we have here the problem "microsoft flight simulator" drivers talk with real drivers.

any real commercial driver knows how to get full rated thrust from a derated situation.

firewall the lever will of cource only work in a FADEC engine, otherwise you have too look at redlines.

anyway... its no way this question comes from a real 777 driver.

aerobat77,

Your quote - "anyway... its no way this question comes from a real 777 driver"

Be afraid, very very afraid that there are numerous B777 pilots 'out there' who do NOT have an understanding of the points being discussed here! (That includes Command Trainees who have had 7 to 8 years in the Right Seat of the B777 prior to command).

Regards,

Old Smokey

OS

I agree, it is amazing how many pilots who are very unversed in the fundamentals of performance. In the US, my experience base, is that the regulators have dumbed down the tests for ATPL, so the schools have only taught the dumbed down test and finally, performance is taught in the afternoon after a heavy pasta lunch.

In any case, this is a rather basic problem, but I'll bet a large percentage of line F/Os don't understand it. The basic physics are not difficult, just a lack of thorough explanation. Anyone, for a link to ALL the Pprune discussions on this subject?


No bad aspersions on the OP, btw.
GF

We need to keep it all in perspective, though -

(a) if you take on cumulus granitus .. you lose

(b) if you overstress and pull off the wings .. you lose

(c) etc.

As Roger G (AN ops eng boss for quite some time) used to observe .. "the pilots give us a hard time on performance but never seem to hassle the structures guys about the tin bits"

In an ideal world, flight crews would have a basic working knowledge of all the supporting engineering stuff .. it's just that the ops engineering areas (weight and balance, and performance) are two areas in which crews can either be a very useful last ditch safety link in the mishap chain .. or, conversely, foul things up really quickly. Hence these topics tend to get the lion's share of the attention.

It only takes a couple of runway limiting departures where the pilot observes the upwind threshold markings disappear under the nose before liftoff to really get the attention focussed on the sensible need for a bit of understanding of performance matters.

performance is taught in the afternoon after a heavy pasta lunch.

that's the really sad bit. And the reason why we encourage all these sorts of techo discussions on PPRuNe .. the defacto background pilot engineering endorsement program ...

The loss of an engine will pull the stops out. Thrust is derated by the use of program plugs on the EEC's, the pilot does not have access to rated thrust.

OS,
I am VERY clear on the implications of TOGA power being (mis)used post a V1 cut especially with low weights and thus low Vmca. You hit TOGA,the BRT's churn out max un-derated thrust @ 115k a piece! And then the issues of low flight regime controllibility etc etc(I was personally involved with the removal of some very 'set' ideas WRT usage of TOGA post V1 cut).
That's a taken.
So's the fact that one would be have to be very circumscept in its use at especially low weights and as such constitutes additional briefing(at the very least) IF and WHEN TOGA would be used post EF on T/O roll in very low weights...ie obstacles,windshear etc etc.
That said,I completely agree with John.T in that a derate is tantamount to an engine change with a lower max power.Therefore,firewalling the engines ON TAKE OFF ROLL,having used assumed temp+derate would only give me max derate power...
Which gets me back to my original question ..:cool:
PS-Just to keep u in perspective..errm,I am not a '7-8 year RHS flown FO with little understanding of the t7'. Am just doing some brainstorming here.And happens to be some valuable brainstorming,by what I see...
Just so we're on the same page please. No offence here..
Thanks all

It depends on the engine, but the program plugs deliver the RATED THRUST.

Once again the answer is that it depends on the engine, you will find that a lot of aircraft operate with Fixed Derate and Assumed/Flex Derate which are lower than the RATED THRUST and are controlled by the pilot.

Mutt

In tech training right now on the B77f, asked the instructor these direct questions. Have access to the origional books (co ones used). Guess the old saying is true... Those who can do, those who can't teach.

Taking in mind the MD-11 fadec bar, I could not understand how an aircraft could be manufactured W/O access to full thrust/exceedence if needed. I learn more here. THX

That might be true for the 777, as the 737 was mixed in here before, it is not true on that type. Max rated thrust is available with a second TOGA click or simply firewalling the thrust levers, which leads to the sound advice to not touch them in case of an engine failure past V1 especially at low weights or V1s (which can be below 100kts).

1) Why touch the TOGA button after engine failure? The calculated derate covers the obstacle clearance. It is just (sometimes) a long sit to flap retraction altitude.
I specifically brief the use of derate and the dangers involved as we not do it on a daily basis (empty/postitioning flights).
2) I always wondered wy the assumed temp will not go beyond 60 degrees C (in my company, B737). Is there as special reason why not to allow 100 degrees??? It gives the benefit of not to worry about V2min etc...

25% limitation on thrust reduction limits the practicality of the assumed temperatures provided to you.

In some cases, Airbus have obtained approval to operate with Flex thrust reductions of -40%, in these cases you will see assumed temperatures in the 70's.

Mutt

In the B737 you can get full rated thrust on the N1 indicators. Firewall or 2nd TOGA. Whether the trottles will follow automatic, is another thing.

So no new replies yet...and the mystery still lingers..
;)

From what I understand as studied and been told by experts. For the GE90-115b, my operator has a hard EEC program plug derate to 110k, does not matter how many times you click TOGA you get 110k.

Your company restricts max thrust under contract with the engine manufacturer (in some cases for overhaul contracts) or on their own to the thrust allowed by the hard wired program plug on the eec. My previous post to engine out was false. All of your limiting performance data is based on this.

Full rated thrust as a pilot understands is the limited thrust by FADEC, you will get no more as the GE-90-115 is capable of 127k as I hear in the test cell. Rudder authority in an engine out situation would not compensate at 127k and engine wear (overhaul contracts) are based on the hard de-rate setting (more hrs on wing in between)

Not the case with my company.
I have a choice of three (fixed value) derates to choose from. And then I can do an assumed temperature on either. Thus the question..
All these derates are selectable from the FMC and the Vspeeds are calculated accordingly,after the derate value has been selected and the assumed temperature plugged it.

KOW are you speaking of max flex (from what I understand on the -115 is limited to 20% less than max derated), TOGA is 10% less than max de-rated then 2nd click TOGA that brings you up to max de-rated thrust.

I am talking GE here and do not know but expect by example it would be the same for the -94 etc.

I don't fly a boeing, but E170/E190's.

The posters question seems pretty reasonable. We have TO-1, TO-2 and TO-3, all of which we can flex.

Most of the guys in work are surprised to learn that if we use TO-3 with a flex, it does not matter how hard or how far we push the thrust levers, we are not going to get any more thrust than TO-3 no flex, with 2 exceptions.

1. Windshear will give WSHR thrust.
2. Engine failure will give us Reserve power, but only TO-3 reserve.

If we have completley messed up our performance, and the end of the runway, or an obstacle is rapidly approaching and we wan't to get away from TO-3 flex to TO-1, then some very quick FMS programming would be required.

Read all throught this and some interesting points made, claims, counterclaims etc. The only thing that does seem clear, is that there are many, many who think they know but actually don't.

Just wondered, why - if using de-rate you would ever want full flat rated power anyway.
Apart from the issues with vmcg, all your obstacle clearance for engine failure is covered by your weight tables anyway. So providing you RTOW is derived from the derate/assumed method you have all the power you need even with an engine failure at T/O.

My understanding is the most engine failures at T/O are at full stress, so to increase the EGT on your remaining engine (when the power you have will already suffice) puts an increased risk that you will lose that engine too?

@ORJ

There is no guarantee that in a real-world failure scenario that you "have all the power you need even with an engine failure at T/O". The certification rules for determining single engine failure performance are specific, and not all-encompassing; there are failure scenarios that will result in losing more performance that is assumed.

So while there are very good reasons to leave the thrust where it is supposed to be - VMC not the least of those - someday someone will wish they had the full rated thrust, not the available derated max.

One example, is any failure which causes the failed engine to fail to windmill. The additional drag for a locked fan is considerable.

Care to elaborate ... ?

Ok. You take off at a long runway. no obstacles. I speak for the B737. You derate, and probaly use ATM for your take off. Your engine rating is now 22k.
Your destination is 30 min further on, rwy with on the other end obstacles. In the event of a go-around here, you do not want to rely on a 22k derated engine, but full go around thrust. Especially if you would loose an engine. So TOGA (twice) can give you 26k..

before you depart should you not check your LDA/weight restriction at planned airfield and alternates for a) most favourable and b) most likely (due WX forecast etc.) and then ALSO check your go-around gradient limiting weights?

If these are lower than your current RTOW, you need to reduce it further - de-rate, assumed or normal take-off?

that's what I thought.

so when you derate say 24k it stays 24 till you land ?

No, it goes full thrust on 2nd Toga. Also just after T/O. That is exactly why you should not do it, but advance maximum to the green N1 indicator, which is your derated trust. (Not the double derate with ATM included). Pushing TOGA moves the N1 indicators up to full trust.