Define V1, Vr and V2, and tell me what changes if the runway is contaminated.
What they are really probing: The opener in almost every technical interview. They are checking you can define terms precisely and then apply them, not recite them.
Model answer
Define each one as a decision or a state, not as a speed on a card. V1 is the maximum speed at which the first action to stop must be initiated for the aeroplane to stop within the accelerate-stop distance available; past V1 you are going flying. Vr is the speed at which rotation is initiated so as to reach V2 by the screen height. V2 is the takeoff safety speed — the minimum speed to be achieved at 35 feet with the critical engine inoperative, giving the required climb gradient. Then apply it: on a contaminated runway the accelerate-stop distance grows because braking action is degraded and reverse credit may be limited, so V1 reduces, and the gap between V1 and Vr widens. That means a longer period where you are committed to stopping, and a rejected takeoff near the new V1 uses far more runway than the dry case. Say what you do with that: on contaminated performance you brief the reject decision more carefully and you set your threshold higher — above 80 knots the reject list is short, and on a contaminated surface you want it shorter still. Finish with the airmanship point rather than the number: the risk after V1 is not the engine, it is the pilot who tries to stop anyway. A board will accept a definition delivered slightly imperfectly; they will not accept a candidate who cannot say what the number is for.
What fails this question
- — Reciting V1 as 'decision speed' with no mention of the action having to be initiated by then
- — Saying V2 without reference to the critical engine inoperative or the screen height
- — Not knowing which way V1 moves on a contaminated runway
- — Treating it as a memory test and never connecting it to the reject decision
Follow-ups they ask next
- — What is your reject policy above 80 knots?
- — What happens to V1 if you use reduced thrust?
- — Who calls the reject on your current aircraft, and why that person?