View Full Version : FLEX V1 vs. TOGA V1

16th Sep 2007, 23:53
Should a pilot be able to select TOGA during a FLEX takeoff?

Was watching a video where an A340 crew (for the heck of it) decided to use full thrust. If limiting weight was induced by a high VMCG, would selection of TOGA cause a problem with the takeoff in the event of an engine failure?

Any other problems with doing this? Or are my thoughts flawed.


17th Sep 2007, 01:55
First - a matter of definitions:

FLEX is based on A RATING plus an assumed temp. The RATING can be either the nameplate rating of the engines, or a derated value (can be either -10%, -20%, etc. OR an earlier engine rating). Thus under a 20% derate (=80% of nameplate), then FLEX might take you to as little as 60% of nameplate thrust (=80% x 75%).

If the EFATO after V1, you can advance to the baseline rating - in other words VMCA and VMGC have not been compromised by the FLEX selection.

However, if the rating used is -10%, for example, and a FLEX TO is based on that -10% value, then you can only safely advance to the -10% rating. If you go to full nameplate rating then all bets are off. :8

17th Sep 2007, 04:31
VMCG is calculated with the appropriate RATING at the outside air temperature in order to permit you to increase the thrust during the takeoff, however as Barit1 has stated, you must stay within the RATING.


Sirius Flying
18th Sep 2007, 22:41
I agree with last post. With FLEX TO you will never have problems with VMCG should you decide to increase thrust at some stage. However, with DERATED TO, don't move the levers, as benefit of decreased VMC is taken.

18th Sep 2007, 23:06
It's not necessarily as dramatic as suggested ..

(a) pre takeoff, check the speeds for a full thrust takeoff ... if your schedule is above then the min speeds are not a problem. Otherwise, be very careful ... but you should be on a VERY short runway in such circumstances .. and, if you get a failure, you will have your hands sufficiently full that pushing up the throttles will take a while to come to the top of the to-do-list. With the associated low weight takeoff, the likelihood that the speed increase won't have taken you well out of the danger zone is low.

(b) in any case ... if you do choose to increase thrust, do so SLOWLY. It is not unheard of for a rapid thrust increase to catch the crew out .. I recall one accident investigation with which I was involved where just this probably was the final straw which broke the camel's back in the initiating sequence of events leading to a nasty fatal pile of charred aircraft ...

Brian Abraham
19th Sep 2007, 05:11
Could you please advise the accident referred to at (b).

19th Sep 2007, 05:40
Brian .. per pm ...

19th Sep 2007, 09:11
John - me too if it is not too much trouble - or post if easier.


20th Sep 2007, 09:41
However, if the rating used is -10%, for example, and a FLEX TO is based on that -10% value, then you can only safely advance to the -10% rating. If you go to full nameplate rating then all bets are off

Barit1, could you please explain when you say the "rating" used? I'm sorry I just don't see exactly what you mean. Do you mean the rating of the engine as in set by the manufacturer? Where do you set the thrust levers to set the -10% rating?

If I flex on my current type(A320) or used T01/T02 on Boeing and engine failure after V1, assuming say a non-limiting runway, I always assumed you could either leave thrust at selected flex/derate or advance to TOGA(admittedly more to do with attaining screen heights and climb out).

Cheers :ok:

20th Sep 2007, 12:40
Well I have a doubt on that... Recently my airline policy is to use TOGA at all takeoffs when the runway is wet... Question: Let's say the aircraft is really light, when consulting the airport analysis should I use the appropriate speeds for the actual weight (limited to the minimum speeds) or should I use the speeds for TOGA (maximum takeoff weight for this condition).
In the situation above does not sound good to takeoff on TOGA and use such low speeds, on the other hand does not sound good either to be so light and use such high speeds...

20th Sep 2007, 14:02
The AFM will (usually) have separate performance chapters for rated TO (identified by the engine model), plus one or two derated TO (-10, -20, etc.) chapters. Any of these may be used given appropriate TOGW, r/w available, ambient conditions etc.

If you derive your FLEX TO data from one chapter, the max thrust you can safely use after a V1 cut is the N1 or EPR FROM THAT CHAPTER. (Albeit JT points out some additional pre-TO checks you can make...)

Does this help?

20th Sep 2007, 22:41
If an aircraft has an engine failure where applying maximum thrust on the remaining engines would cause loss of directional control, does it mean that the pilot should increase the thrust only to whatever is safe given the airspeed and crosswind, then as the plane continues accelerating gradually increase the thrust to the maximum possible?

20th Sep 2007, 23:52
.. folk are tending to worry a bit too much about a particular corner of the envelope. It's useful, even necessary, that you should be aware of the concerns .. but it is not necessary to get ulcers about it all.

(a) the takeoff will be (or should be) planned and predicated on meeting all the rule bits for that takeoff, including the consideration that whatever level of flex and/or derate is used is all that is required ... ie unless something dreadful happens, there is no need to increase thrust .. and, indeed, doing so can create problems unless that is something for which you train in the box .. ie you are used to the exercise

(b) the Vmcg/Vmca concern only raises its head for very light takeoffs when the speed schedule is very low and, depending on the aircraft Type, may get down in amongst the Vmcg/Vmca weeds

(c) if the speed schedule is moderately above Vmcg/Vmca then there is no real concern to be had .. although it is much more sensible to advance the throttles slowly if more thrust is your need for some reason on the day

(d) one of the basic concepts underpinning Type Certification is the idea that the throttles are NOT TO BE reset during the takeoff ... so the pilot should NOT increase the thrust setting unless there is some very good reason to do so. I suggest that the reason that it "gives us a bit for mum and the kids" is NOT a good enough reason to complicate the situation at a time when you already are more than busy enough ...

21st Sep 2007, 01:40
Thanks Barit1 and John Tullamarine, cleared it up a bit alright. So when I select a derate temp and use the associated speeds, if I have an engine failure then technically I shouldn't increase the thrust. Once I'm above Vmu and airborne is there a problem with Vma with increasing thrust?

JT, I agree with your last point it doesn't make sense to increase the thrust "for wife & kids" when the current thrust is enough to climb you safely away, especially if you're having difficulty controlling the aircraft at the time....bad situation worse imho.

Anway thanks for the replies. :ok:

21st Sep 2007, 02:34
... above Vmu and airborne is there a problem with Vma with increasing thrust?

There may or may not be. If you are of the persuasion that increasing thrust during an OEI experience is good, then you need to know the following - either

(a) TOGA, on your aircraft, only runs the thrust up to the derate value .. in which case, that might be fine provided that the increase from derate/flex to derate is slowish and smooth ... or

(b) if you are going to run up above the derate, either via TOGA or Mk 1 fistful of throttles, then you MUST know what the full rated minimum speeds are and respect them. You can get a handle on this by consulting the RTOW charts for full and derate thrust pre-takeoff.

.. if you're having difficulty controlling the aircraft at the time ..

for a low weight, speed limiting takeoff, I would think that one should anticipate having an interesting ride .. if you haven't looked at this in a reasonably realistic box first .. then things might get out of hand very quickly. I used to insist on first endorsements on Type, especially initial commands, being exposed to rated thrust, minV1, aft CG, etc., OEI failures ... after the first few exercises with the usual departures, the guys would get their acts together and get on top of the stick and rudder aspects of the problem .. like anything else it all comes with practice. However, not something to be attempted for real without any prior exposure ..

21st Sep 2007, 11:13
Thanks for the info.

Happy flying.