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Flying The Alpha

Angle-of-attack indicators come to general aviation
Garmin AOA on G3X Flight Display
The FAA is finally recognizing what the military has known for decades: angle-of-attack (AOA) indicators save lives. The federal agency took a huge leap forward in adopting AOA indicators in February when it announced the simplification of design approval requirements for them. "Safety is our top priority, and with today's announcement, we are improving safety by streamlining regulations and cutting red tape—a win-win situation," said U.S. Secretary of Transportation Anthony Foxx.

Loss of control is the number one root cause of fatalities in both general and commercial aviation. Currently, in GA alone, we're averaging one fatal loss of control accident every four days. Inadvertent stalls and spins are implicated in half of all GA approach and descent accidents, and 60% of them happen on takeoff and landing. Clearly, something needs to be done because pilots just aren't getting it.

The root of the problem occurs in primary training. Though AOA is taught as a theory to private pilots starting out in ground school, in the air they rely on speed, memorizing the stall speeds shown in the POH. Soon, it's the stall speed that pilots become fixated on, and they forget that speed has little to do with stalls and spins.

The problem with airspeed alone is that an airplane can stall at any speed, any attitude and any power setting. The stall speeds published in airplane flight manuals are only valid for unaccelerated flight (1-G load factor), coordinated (ball centered) and at one weight (most typically max gross weight). But, these conditions are rarely met on real-world flights. Consequently, speed itself isn't a reliable parameter to avoid a stall.

AOA, as we all learned, is the angle between the chord line of the wing and the relative wind, or flight path. John Cox, CEO of Safety Operating Systems, put it beautifully when he said, "Angle of attack is simply the difference between where the wing is pointing and where the wing is going." AOA is a better parameter to use in avoiding a stall because, for any given configuration, the airplane will always stall at the same AOA, also known as the "critical AOA." This stall AOA doesn't change with weight, temperature or density altitude. AOA indicators can help pilots detect this otherwise invisible wing (airfoil) position and avoid a stall.

Alpha Systems AOA
Of course, military pilots have been flying by AOA for decades, instead of relying on airspeed alone—especially on approaches. They call it "flying the alpha." However, civilian pilots seem to just be discovering the idea of AOA, though it has been around since aviation began. In fact, awareness of the AOA at any given time is an art and is attributed to the world's best pilots. I have a friend who's fond of saying, "Be the wing," meaning, be aware of the AOA. This fine art isn't easily learned, however, without much practice. In today's overly technical cockpit environment, stick-and-rudder skills like AOA awareness seem to be fading. The current movement to equip GA aircraft with AOA indicators is a step toward helping pilots discover the importance of this critical parameter.

Although AOA indicators have been available in military and commercial turbine aircraft, the effort and cost associated with gaining installation approval has limited their use in general aviation. The streamlined requirements are expected to lead to greater use of the devices and increased safety in general aviation.

"We have eliminated major barriers so pilots can add another valuable cockpit aid for safety," said FAA Administrator Michael Huerta. "These indicators provide precise information to the pilot and could help many avoid needless accidents."

Under the new policy, manufacturers must build the AOA indicator system according to standards from the American Society for Testing and Materials (ASTM), and apply for FAA approval for the design via a letter certifying that the equipment meets ASTM standards and was produced under required quality systems.

Though AOA indicators aren't a cure-all for eliminating accidents, they're another source of information for pilots. Their purpose is to warn pilots when they're entering the stall realm so they can react faster than a traditional stall warning might allow. Manufacturers are jumping on this potential bonanza with Garmin announcing that their GI 260 AOA indicator would be available in the third quarter of this year. BendixKing has their KLR 10 available now, and Alpha Systems has several AOA kits available, as well. Safe Flight Instruments offers a "lift detector" that works with their stall warning product. More manufacturers are expected to offer AOA indicators in the coming months.


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