Reasons to perform a rejected takeoff vary but are usually related to a suspected or actual problem with the aircraft, such as an engine failure; fire; incorrect configuration; aircraft control issue; unusually slow acceleration; automated warning signal(s) indicating a critical system failure; environmental conditions such as predictive windshear; or an instruction from air traffic control.
If the airplane's ability to fly is in doubt (for instance, in the event of a major flight-control failure which leaves the airplane unable to rotate for liftoff), the best option may well be to reject the takeoff even if after V1, accepting the likelihood of a runway overrun.
The autobrake system will automatically apply maximum brakes if throttle is reduced to idle or reverse thrust during the takeoff roll once a preset speed has been reached.
The RTO test is performed under the worst possible conditions; i.e. with fully worn out brakes, the plane loaded to maximum takeoff weight and no use of thrust reversers.
Small brake fires are acceptable, providing that in the first five minutes, they do not prejudice the safe and complete evacuation of the aircraft.