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.
The FAA’s action came in the form of a Special Airworthiness Information Bulletin (SAIB 2024-07), “Stall Warning System, Angle of Attack Alerting Systems,” written to “help general aviation aircraft owners and operators understand the importance and safety benefits of angle of attack (AOA) alerting systems” on FAR Part 23-certificated airplanes, including those operated under FAR Part 91. According to the SAIB, “Increasing awareness of the benefits of these alerting systems may reduce the risk for loss-of-control (LOC) incidents and accidents.”
Angle-of-attack indicators are not new to general aviation, but they have become more widespread. Under a policy the FAA adopted in 2016, “Approval of Non-Required Safety Enhancing Equipment (NORSEE),” the agency streamlined its approval process for equipment that can “measurably increase aircraft safety.” As one result, AOA indicators became much easier to install as advisory equipment—useful, but not required.
As a result of the Colgan Air crash, the NTSB recommended that the FAA “require installation of low airspeed alerting systems that provide pilots with redundant aural and visual warnings of an impending hazardous low speed condition” on all airplanes operated under FAR Parts 121, 135 and 91, subpart K.
Instead of making a new rule, the new SAIB was developed “to advocate for the voluntary adoption of low airspeed alerting systems as standard equipment on new aircraft” certificated under FAR Part 23, i.e., small airplanes.
The SAIB goes further. It “recommends” all Part 23 airplanes, plus experimentals, “Install and calibrate critical AOA alerting systems” and that pilots “Receive training on the use of AOA indicators and how to incorporate them in instrument scans.”
