Class A aircraft use VSR, the stall reference speed, rather than VS1 but it is substantially the same thing. The take-off safety speed is the highest of:
 1.13 VSR for two-engined and three-engined turboprop powered aeroplanes and jet aircraft without provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed.
 1.08 VSR for turboprop aeroplanes with more than three engines and jet aircraft with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed.
 1.10VMC
 VR plus the speed increment attained before reaching a height of 35 ft above the take-off surface
 A speed that provides adequate manoeuvring capability