Take Off Perfomance
I had a discussion with a colleague about take off performance; essentially, the topic was the use of assumed temperature and the choice of speeds for V1,Vr and V2.
His assertion was / is that we should use the speeds associated with the weight which corresponds to the assumed temperature. I disgree: I believe that we should the speeds corresponding to our actual TOW. The FMC, interestingly computes Vfr and Vfto based on the actual weight.
His belief is that by using the higher speeds we are also employing the improved V2 climb technique, however, I am of the opinion that we can only use that technique when we have unused distance available on the runway and we are WAT limited (climb limited).
Taking the issue to extremes to highlight the point, if our airplane MTOW is 300 tonnes ( ISA, still air, 3000m TORA/ASDA/TODA, Dry,no obstacles - basically everything going for us) but today, same conditions, we weigh 250 tonnes, we should use the 250 tonne speeds even if we tell the engine computer that the assumed temperature is +55 and the RTOW at that temp is 300 tonnes !
If we had a limiting obstacle, using the higher speeds (OK I concede that at 250 tonnes we would go up like a rocket with all 4 turning / 2 turning), would keep the airplane on the ground longer; TODR increases and the distance to the obstacle reduces. Additionally, the obstacle domain changes as the end of the domain is based on the end of TODR, thus another obstacle, not accounted for in the analysis, could be introduced.
I think he is confusing saving engine life and the improved V2 climb technique but would be grateful of a more scholarly input.