Inadvertent touching of brakes in 737 during takeoffroll
Thought this might be useful information for simulator instructors and in real life.
Event: Teaching new students(250 hours each) the step by step sequence of actions for a rejected take off roll. The simulator was set so that if all actions performed correctly the aircraft would stop with 100 metres to spare. Abort speed was 100 knots with instructor calling "STOP" at 100 knots and then standard abort actions taken by PF. The instructor IOS has a pop-up picture that activates as soon as brakes applied, whether autobrake RTO or manual braking. You can see if brakes applied equally as in RT0 or unevenly if manual braking (often happens). The latter invariably extends the abort distance.
First student consistently did well and stopped with approx 50 metres to spare. Second student actions were fast and correct yet he consistently over-ran the end of the simulator runway and causing much scratching of instructor's head to determine why the over-runs,when the student seemed to be acting correctly. During another takeoff run by this student, the instructor just happened to glance at his own instructor screen and was astonished to see the brake pop-up picture appeared and indicated rapid variation of braking taking place at very low values but nevertheless it was obvious, although nothing felt through the simulator. The indications being the student was inadvertently applying some braking during the take off roll. This explained the over-run as the takeoff roll was being extended due to brake drag.
The student vehemently denied touching the brakes during the takeoff roll. OK, that was put down by the instructor to a possible ethnic loss of face culture thing. A recorded picture of the instructor screen was used to demonstrate that brakes were indeed being activated; albeit spasmodically. . The point of mentioning this event in Tech Log is to point out to line trainers that unless the aircraft jerks slightly during the takeoff roll signifying possible inadvertent touching of the brakes, it may be impossible to know if slight inadvertent brake operation is happening which may invalidate V1 and worse still cause heat build up in the brakes and tyres. All the more reason to emphasis to new pilots on type, the importance of proper toe positioning on the rudder pedals for take off i.e. at the bottom of the pedals