As prop jet says, Airbus makes use of the full length of every runway in their performance and reduce the thrust as much as possible to a minimum allowed value. You're most welcome to use more thrust, or TOGA, which would shorten the take-off length. Most airlines promote the Flex take-off for engine life/cost.
Thrust may not be flexed below 25% (A340-300) 40% (A340-500) ref FCOM 2.02.01 pg 14, of the entire thrust and all climb gradient segments must be made.
This is to say, that on a wide body in general, medium to long flight, you will always be having the opportunity to visit the far end of most runway rather closely when rotating.
Screwing up the figures or weights, will always have a disastrous effect.
Last edited by Jetjock330; 1st Apr 2009 at 15:32.