Flexing

[Lump Jockey]

When taking off using FLEX/with FLEX (or however it's said!), is it (a) up to the pilot if it should/can be used, and (b) does it effect the distance left remaining after V1? (I would have thought yes).
Thanx.

[Dragon Knight]

Reduced takeoff thrust (FLEX) wil normally increase the required runway length and can be used when there is a margin between actual takeoff weight and the runway limited weight.

Yes, the distance to the runway end after V1 will be less, but sufficient to stop on the remaining runway, or continue the takeoff on remaining engine(s) and still be airborne at runway end.

[RadarContact]

Usually the power setting (FLEX or TOGA) isn't the only variable. For exaple with TOGA power you could either lift off after less runway, creating more stop margin. Or you could roll longer (higher V2 ) to increase climb performance. If runway length permits, of course.

The goal usually is to find the optimum balance between these two extremes. Same applies for FLEX power, only that a new variable enters the scene: engine stress and wear (which is reduced by using FLEX in the first place).

[Lump Jockey]

thanks guys, nice one! i saw on Airliners.net that someone sent a picture in (in their discussions forum) and started talking about it saying he could tell by the photo that the A340 was flexing! how can you see it?!

[RadarContact]

The power levers are in different positions for FLEX or TOGA. Also, if the ECAM CRTs were visible on the photo, it would have been recognizable there.

[Lump Jockey]

The picture is taken from the ground as the plane goes by!

[RadarContact]

The answer would be a no then...

[Seba]

and what if he meant wing flexing?

[mutt]

If you knew where the A340 was flying to and looked at the amount of runway used before liftoff, you could have a good guess about the use of Max or Flex thrust.

Apart from that, there is no external way of knowing what thrust rating was used for any particular takeoff.

Mutt.