Unlike in a car, where a stall involves an engine cutting out, an aircraft stall has to do with a lack of air moving over and under the wing. Air moving over and under the wing creates lift to keep the plane in the air, and a stall occurs when a plane’s nose reaches an angle of attack which skews the lift-to-drag ratio for the wings. Put simply, when a plane stalls, there is not enough air flowing over the wing to generate pressure underneath the wing and create lift. The ability to recover from a stall and control a stall are necessary skills for any pilot and are required to get a pilot’s license.
Stall recovery requires a large amount of altitude. Because a stall means the plane is no longer traveling at a speed to generate enough air flow, stall recovery requires regaining enough speed. So, a pilot must somehow increase the speed of his or her airplane. This is most easily done by entering into a dive in order to gain speed. This means a plane must have a good amount of altitude, usually at least a few thousand feet, depending on the seriousness of the stall and the size of the plane, in order to dive. While stalls are nerve-wracking but not necessarily a problem when they occur high enough up, they can be deadly at a low altitude. Along with altitude, control can be difficult if the plane enters a flat spin or a deep stall. This means dropping the nose of the plane and entering into a dive will not necessarily improve the situation, and the aerodynamics of the plane can contribute to the difficulty. In cases like these, certain features on the plane can help the pilot: alert systems include stick shakers, stick pushers, or loud buzzes, and vortex generators, anti-stall strakes, stall strips, and spoilers can mechanically help a plane not enter into a flat spin or deep stall. In most commercial aircraft, an on-board computer keeps the plane from ever being able to reach the angle of attack necessary to start a stall.