Knowing the margin of your safety
Anyone who has reached a hand out the window of a moving car has had an object lesson in angle of attack. Tilt your hand upward and feel both lift and drag increase. Move it in line with the airflow and resistance diminishes. The angle at which your palm (chord line) meets the passing air (relative wind) is the “angle of attack”—a vital measure of the amount of lift the wing is generating, and its nearness to the critical angle at which it stalls. Unlike airspeed, angle of attack indicators give pilots a direct measure of lift—and that allows them to fly at the optimum wing angle despite varying aircraft weights, density altitudes, and flap and landing gear configurations.
Angle of attack isn’t pitch attitude.
A fighter jet climbing vertically at high speed has a low angle of attack. An aerobatic airplane pointed straight down on the back side of a loop has a high angle of attack.Keep in mind that an airplane can stall at any airspeed and attitude—but the wing always stalls at the same critical angle.
On final approach, the pilot adjusts aircraft pitch and power to keep the wing at the optimum angle of attack. By flying at the proper angle of attack, the pilot maintains a safe margin above stall without carrying excessive speed.
What the AOA indicator is telling you
AOA systems used to be heavy and expensive, but a new generation of noncertified equipment has made them much more affordable. The FAA is encouraging the use of noncertified AOA systems in general aviation aircraft to help reduce loss-of-control accidents, which account for up to 40 percent of GA fatalities. AOA indicators can be used either as a secondary reference or—as with the Icon A5—the primary pitch and power instrument. As the little wing climbs in the yellow, you know it's time to either add power or reduce back-pressure.
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