Extract from QRH;
“Rejected Takeoff
The Captain has the sole responsibility for the decision to reject the takeoff. The decision must be made in time to start the rejected takeoff manoeuvre by V1. If the decision is to reject the takeoff, the Captain must clearly announce “STOP,” immediately start the rejected takeoff manoeuvre and assume control of the airplane. If the First Officer is making the takeoff, the First Officer must maintain control of the airplane until the Captain makes a positive input to the controls.
Prior to 80kt, the takeoff should be rejected for any of the following: • activation of the master caution system
• system failure(s)
• unusual noise or vibration
• tyre failure
• abnormally slow acceleration
• takeoff configuration warning
• fire or fire warning
• engine failure
• predictive windshear warning
• if a side window opens
• if the airplane is unsafe or unable to fly.
Above 80 knots and prior to V1, the takeoff should be rejected for any of the following:
• fire or fire warning
• engine failure
• predictive windshear warning
• if the airplane is unsafe or unable to fly.
During the takeoff, the crew member observing the non-normal situation will immediately call it out as clearly as possible.”
The assumption is that a genuine configuration problem will be obvious on hitting TOGA at the start of takeoff and below 80 kts.