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Decision Speed


V1 is the Decision speed (sometimes referred to as critical engine speed or critical engine failure speed) by which any decision to reject a takeoff must be made. Above V1, the takeoff must be continued unless there is reason to believe that the aircraft will not fly. An engine failure identified not later than V1 should always result in a rejected takeoff.

If the decision is made to reject, the aircraft can be brought to a stop within the Accelerate Stop Distance Available (ASDA). If the decision is made to continue the takeoff, either in a non engine failure case which occurs prior to V1 or in an engine failure case which occurs at or after V1, the aircraft can get airborne and achieve or exceed the appropriate screen height within the Takeoff Distance Available (TODA). If a reject is initiated at a speed above V1, a runway excursion is probable.

Stopping the aircraft within the confines of the runway or safely continuing the takeoff is predicated on an appropriate and timely stop/go decision and the corresponding appropriate and timely actions. The V1 call should be made such that the call is complete just as the speed is achieved. If a reject decision is taken, it is critical that stopping action is initiated within two seconds and that full stopping device capability is utilised. If the takeoff is continued, the yaw due to engine failure must be corrected, the aircraft rotation must occur at Vr and the appropriate climb speed must be maintained to guarantee that the screen height will be achieved.

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