Originally Posted by
390cruise
Am I a little out of date if I recall that in the V1 continue case we will clear the end (screen height) by 35' or more if the all factors are correct?
Whatever the specific height is achieved (a function of the rules and conditions assumed) it needs to be borne in mind that the calculation is valid only for the conditions assumed. Specifically for engine failure, it is assumed that the engine (or at least the fan, for sure) is windmilling; if it locks for any reason, which may be the same reason as causes the failure, the performance sums are out of the window and all bets are off.
Originally Posted by
390cruise
I strongly believe that most Airline jets depart at up to 5% above the takeoff mass shown on the load sheet.
I'll pretend I didn't hear that .. la-la-la.
Originally Posted by
390cruise
Also at high masses Vmca is not a problem, while at low masses thrust is not such a problem and anyway speed tends to run away!!!
Correct for the first part, for the second, not if you have flexed to the max - you just made a low weight takeoff climb or distance limited as well.
An additional thought, which follows from my first point, which is that the need for increasing thrust above the planned level to actually climb may arise due to a failure case not considered in the performance calcs - that same unanticipoated failure case is likely also outside the scope of the failures assumed for handling, and the official VMC may now be purely notional.
Indeed, in a worst case scenario with a locked fan, say, not only is the drag well above the assumed levels resulting in badly degraded performance, but the drag is also increasing the control requirements even WITHOUT increasing the thrust, and it may in fact be impossible to square that circle. Some failures will not be survivable... no matter what you do with the thrust levers.