Heels on the floor every time. During abort training in the 737 simulator, the scenario was set such that a well handled abort using manual braking and both reverse thrust levers would stop the aircraft with 100 feet to spare. The crew consisted of two Asian cadets. One consistently pulled up within the runway while the other always over-ran by a hundred yards or more despite completely correct abort actions.
By chance I happened to look at the brake pedal pressures on the instructor panel during the take off run and saw the pressures cycling rapidly between 100 psi to occasionally 300psi. The cadet who over-ran the runway on each abort was unknowingly applying brakes during the take off run because his feet were high up on the pedals. This extended the runway length needed to V1 and invalidated the abort.
It was impossible for the instructor or the PNF to actually see the cadet's feet applying the pressure because it was dark in the cockpit and in any case it is not the sort of thing you look for in the middle of a take off run. To get the point across, I got the PNF to sit at the instructor panel and observe the pedal pressures as his colleague acccelerated. He could now understand the problem and conveyed what he had seen to the PF cadet who believed him. Previously the PF had sworn blind he was not touching the brakes...Loss of face etc.
The danger of inadvertant light brake application during the take off run, far outweighs the very remote possibility of an abort just at V1 together with a miniscule delay in sliding feet up the pedals to achieve max manual braking on a limiting runway. RTO is best of the lot but inadvertant dragging of the brakes by light pedal pressure due feet up on the pedals on take off can ruin your whole day. Performance calculations go out of the window. Worse still, you cannot pick it happening during the take off accelleration phase because there are no gauges for pedal pressures.
Following this observation on that occasion, I began to monitor pedal pressure more closely during normal take offs and sure enough it happened on more than a few occasions over several weeks on different pilots.
Last edited by Centaurus; 31st Mar 2006 at 09:47.