Since an airplane can be stalled at any airspeed, a stall indicator referencing airspeed alone would not be an altogether reliable means of determining an impending stall condition. AOA (angle of attack) is the critical component of an imminent stall situation, and as such most aircraft use a means of alerting the pilot when this AOA is reached. Various techniques are employed: Leading edge orifices, tabs, and fuselage mounted AOA vanes are some of the more common methods.