V speeds

In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft.

[3][4] The yellow band is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement.

Proper display of V-speeds is an airworthiness requirement for type-certificated aircraft in most countries.

[15] In discussions of the takeoff performance of military aircraft, the term Vref stands for refusal speed.

It is the speed above which the takeoff will continue even if an engine fails or another problem occurs, such as a blown tire.

[9] The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length, wing flap setting, engine thrust used and runway surface contamination; thus, it must be determined by the pilot before takeoff.