<P> Operations with transport category aircraft employ the concept of the takeoff V - Speeds, V, V and V. These speeds are determined not only by the above factors affecting takeoff performance, but also by the length and slope of the runway and any peculiar conditions, such as obstacles off the end of the runway . Below V, in case of critical failures, the takeoff should be aborted; above V the pilot continues the takeoff and returns for landing . After the co-pilot calls V, he / she will call V or "rotate," marking speed at which to rotate the aircraft . The V for transport category aircraft is calculated such as to allow the aircraft to reach the regulatory screen height at V with one engine failed . Then, V (the safe takeoff speed) is called . This speed must be maintained after an engine failure to meet performance targets for rate of climb and angle of climb . </P> <P> In a single - engine or light twin - engine aircraft, the pilot calculates the length of runway required to take off and clear any obstacles, to ensure sufficient runway to use for takeoff . A safety margin can be added to provide the option to stop on the runway in case of a rejected takeoff . In most such aircraft, any engine failure results in a rejected takeoff as a matter of course, since even overrunning the end of the runway is preferable to lifting off with insufficient power to maintain flight . </P> <P> If an obstacle needs to be cleared, the pilot climbs at the speed for maximum climb angle (V), which results in the greatest altitude gain per unit of horizontal distance travelled . If no obstacle needs to be cleared, or after an obstacle is cleared, the pilot can accelerate to the best rate of climb speed (V), where the aircraft will gain the most altitude in the least amount of time . Generally speaking, V is a lower speed than V, and requires a higher pitch attitude to achieve . Normally ground speed for takeoff varies between 250 km / h to 475 km / h . </P> <P> Assisted takeoff is any system for helping aircraft into the air (as opposed to strictly under its own power). The reason it might be needed is due to the aircraft's weight exceeding the normal maximum takeoff weight, insufficient power, or the available runway length may be insufficient, or a hot and high airfield, or a combination of all four factors . Assisted takeoff is also required for gliders, which do not have an engine and so are unable to take off by themselves . </P>

At what speed does a passenger plane take off