SAE AS439A

This Aerospace Standard establishes the essential minimum safe performance standards for stall warning instruments primarily for use with turbine powered subsonic transport aircraft, the operation of which may subject the instruments to the environmental conditions specified in paragraph 3.4. This standard covers stall warning instruments to provide positive warning to the pilot of an impending stall. Stall, as defined for the purpose of this standard, is the minimum steady flight speed at which the airplane is controllable.