The whole point of the pilots doing the pre-departure performance calculation is so that they can be certain that the weight of the aircraft is such that – given the Takeoff Distance Available (TODA) and the Accelerate / Stop Distance Available (ASDA) - it can be accelerated to a certain speed (v1) and if needs be, at that speed, subsequently stopped in what runway remains (which might see the aircraft entering the 'stopway', but that will see it come to a stop on the paved surface, be that surface the runway or stopway).
Likewise, v1 provides for the aircraft suffering an engine failure at that speed and, if the decision is made to continue the take-off (nearly always the safest thing to do –
and you'll see why in a minute), the aircraft still has enough thrust to continue to accelerate to Vr, become airborne, and achieve the screen height (30' dry runway / 15' wet runway) by the end of the TODA.
On a limiting runway, beyond the performance calculation, the variable factor is the technique the pilots use to stop the aircraft, i.e. if the pilots do not execute correct technique, during a Rejected Take Off (RTO), then the aircraft will go off the end of the runway. The correct technique for stop from v1 is:
- Aggressively close the thrust levers & simultaneously apply maximum braking.
- Pull the speed brake lever.
- Select maximum reverse thrust.
Nb. On aircraft whose engines are fitted with thrust reversers, the use of reverse thrust is not factored into the performance calculation for a RTO that is actioned on a dry runway (but wherein if one uses it, one will come to a stop some distance prior to the end of the runway - or, putting it another way, if one doesn't use reverse thrust during a v1 stop on a dry runway, the aircraft will stop at the end of the runway, i.e. the flightdeck might be over the grass but the nose wheel will still be on the runway / stopway).
On a wet runway use of reverse is factored into the performance calculation and failure to use reverse following a RTO, actioned at v1, will see the aircraft run off the end of the runway / stopway.
Any other variations in the pilots RTO technique (e.g. not selecting speed brakes and / or not using maximum braking, etc.) will likewise see the aircraft run off the end of the runway / stopway.
Needless to say, it is the application of correct technique that pilots practice in the simulator - and it also happens to be part of how the regulatory authorities ascertain that a simulator behaves as the aircraft would prior to approving its use for flight crew training.
If in any doubt about this, have a read of Boeing's Flight Crew Training Manual (wherein I'm certain that Airbus's will read just the same on this topic as it's all governed by the same rules).
For those who might think otherwise, aircraft performance is neither arbitary or guesswork.
Kaptin M - Well said !!!
