Hats off to the FAA for finally suggesting that all airplanes be equipped with angle of attack systems. The agency recently published a special airworthiness information bulletin (SAIB) recommending that AoA systems become standard equipment in new airplanes and retrofitted in existing ones.
As background in the bulletin, the FAA calls attention to the 2009 Colgan Air Dash 8 airliner crash in New York, and the flying pilot’s “inappropriate response to the airplane’s stick shaker” and the resulting low speed and eventual stall. But you don’t have to look far beyond the highly publicized Colgan wreck to find plenty of other ones where the pilot simply didn’t recognize a slow-speed condition by referencing the standard airspeed indicator alone. Never flown with an AoA? I hadn’t, either, until I had a crack at Safe Flight Instrument Corporation’s wing leading-edge speed indexer in the company’s Beech Baron in the mid-2000s. I’ve been a believer ever since. Since Safe Flight invented the stall warning system lift detection system in the 1940s, its AoA tech leverages a similar wing leading-edge sensor for AoA and speed indexing. That’s a photo I captured of Safe Flight’s second-gen system from a demo flight on approach to Waterbury Oxford Airport in Connecticut in the company’s Cessna.
The theory in which Safe Flight’s system measures AoA boils down to the very basic fundamentals of wing lift. Plus, I think a leading-edge lift transducer is one of the most accurate ways of measuring AoA because the system is accurate regardless of aircraft weight, wing loading, turbulence or wing flap configuration. As the aircraft wing moves through the air it divides the air mass. At the center of this divided airflow is a narrow region known as the stagnation point. The location of the stagnation point uniquely represents the wing’s AoA. The system’s lift transducer—installed on the leading edge of the wing—senses the location of the stagnation point by means of a spring-loaded vane. The sensor isn’t a replacement for the aircraft’s stall warning system but is installed in the opposite wing. For an OEM standard, I think the system can work well. The system I flew with used an indexer mounted on the glareshield as you see in the photo, but it’s easy to interface with a primary flight display in both new and retrofit avionics.
Of course, AoA systems have been standard in higher-end avionics for a while now but there are plenty of federated panels that can benefit from aftermarket systems, and while there have been lots of retrofits—and integrated AoA features in Aspen Evolution flight displays and others—I think there can be lots of prevented wrecks with more installations. And now with the FAA advocating AoA equipage for all aircraft, why not sweeten the deal much like it did during the ADS-B Out equipage mandate rush? At the time, the FAA was handing out rebates for qualified installations and it was successful. And now that we have an approved high-octane unleaded avgas that’s being distributed and pumped, perhaps the FAA can focus its efforts and dollars to equip the fleet with AoA systems, while also working on a training initiative so pilots can use them safely. We’ll look at available system options in an upcoming issue of Aviation Consumer.
