Airfoils like the ones built into an airplane’s wing lose their lift when their critical angle of attack (AOA) is exceeded, which can happen at almost any airspeed. When an airplane’s wing exceeds its critical AOA, the wing stalls. What happens next…depends. When a stall catches a crew unawares—as happened aboard Colgan Air Flight 3407 on February 12, 2009, or Air France Flight 447 on June 1, 2009—fatalities are one outcome.
Although the effects of exceeding AOA are well known, there’s no instrumentation required aboard most airplanes that reveals it in real time. There still is no requirement to have an AOA indicator, but the FAA in late December took a major step toward making such equipment standard aboard the airplanes we fly.
