Originally Posted by
mutt
MFS, you dont agree with me......
Well lets see what Mr Airbus has to say....
1: For a given weight it is possible to select a temperature lower than the maximum determined one and keep the speeds defined at the maximum temperature.........
So, by extension, you could use the fully flexed speeds and do the takeoff with full power (as the extreme case of selecting a lower temperature? That would seem to imply that there should be an effect on the speed spread, but you don't adjust Vr/V2 accordingly. That would seem only to be acceptable if you aren't scheduling for minimum V2. Maybe this aircraft is always min Vr?
Originally Posted by
mutt
2: Takeoff must be performed with TOGA (in this example MTOW = 259000 kgs 137/157/166) takeoff speeds for the actual TOW 252000 kgs are increased to MTOW speeds.....
Yet this example shows the speeds being driven by the thrust considerations, which would seem to imply that speed spread IS a concern. Though even here it won't be quite correct as you've got the right thrust but now wrong weight, and speed spread is really a T/W thing at heart.
Originally Posted by
mutt
3: As the performance limited MTOW of 279000 is greater than the structural MTOW of 275000. 275000 has to be retained as the MTOW. Enter the chart with the MTOW to find the v-speeds.
No arguments here - numbers above the structural MTOW can't be used (and shouldn't even exist!)
Not arguing that those are what AB tell you to do, but I think there's something else going on to make those numbers work.
In general I'd also be concerned over trim/rotation characteristics if a speed were used which was appropriate to a (very) different weight - at some point you do invalidate the cert takeoff technique demonstrations.