Mark Korin's small business in Ramsey, Minn., has been building angle-of-attack indicators for the experimental and light aircraft market in relative anonymity for nearly 18 years.
That is no longer the case, thanks to the findings of anand industry committee that studied light aircraft loss-of-control (LOC) accidents. In a final report issued in September 2012, the government/industry General Aviation Joint Steering Committee ranked installation of angle-of-attack (AOA) indicators at the top of its list of 23 safety enhancements that could help cut the problematic general aviation (GA) fatal accident rate. “AOA systems are not in wide use in GA,” the committee concluded. “The GA community should embrace to the fullest extent the stall margin awareness benefits of these systems.”
The safety spotlight, combined with only a few companies who sell AOA systems, has quadrupled Korin's business and has led to a new joint venture with asubsidiary.
The steering committee's action was not a surprise to Korin, a firm believer that the legacy method of teaching general aviation pilots to avoid stalls based on airspeed alone is flawed. Whereas airspeed is an indirect and approximate measure of the lifting capability of a wing, an AOA indicator provides a direct measure of margin with respect to the critical angle of attack, the angle where the wing will stall regardless of weight, configuration or air density.
Korin's company, DepotStar, builds a line of AOA systems that typically includes a probe (separate from the pitot tube) mounted in place of an inspection plate under the wing, a computer unit and a lighted indicator in the cockpit. The indicator is mounted where the pilot can see the colored lights (green is good, red is bad) through peripheral vision while maintaining a focus outside. Along with alerting pilots of dangerous AOA angles, the system also identifies the optimum AOA for landing with a lighted circle, a marker the military calls the “donut.” Military pilots, particularly in the U.S. Navy, are taught to “pitch to the donut” on approaches, says Korin.
Though airliners and business jets come equipped with AOA sensors, the information is typically integrated into the primary flight display and used for automatic stall-avoidance systems, including stick shakers and stick pushers.
For general aviation, Korin says, the primary flight display (PFD) “is the wrong place you want a pilot to be focused on” unless the aircraft is flying in instrument conditions.
One of his competitors, Dynon Avionics, displays AOA on the PFD, but has audible aids to keep the pilot looking outside. A provider of avionics to the experimental and light-sport sectors, Dynon builds a pitot tube with a second hole under the front surface that senses AOA and provides the information to the avionics. While Dynon does not build a dedicated display for AOA, it does have an audible annunciation. “The time when you're going to use it the most is on short final, when you're trying to minimize your workload,” says Mike Schofield, marketing manager for Dynon. “As the AOA increases, you get something that sounds like a Geiger counter mixed with the stall horn—the frequency [of the beeps] increases as the AOA increases.”
This summer, Honeywell, through its light-aircraft avionics arm, Bendix King, partnered with Korin to build a new product called the Bendix King KLR10 “lift reserve indicator,” an AOA system initially for the experimental market but with an eye on the FAA-certified Part 23 light aircraft sector.
Korin is the “technology partner” for the program, which includes his sensor, computer and indicator, redesigned by Bendix King to show the ideal-approach AOA, also known as the “blue meatball,” as well as yellow and red AOA indications and audio alerts for the normal, caution and action-required AOA zones.
Bendix King is selling the KRL10 for $1,600 for the experimental market, but is waiting to see how the FAA will finalize with a planned modernization to Part 23 light-aircraft certification standards before entering that market.
The FAA is considering moving to ASTM consensus standards for certain aspects of Part 23 certification, which would list an AOA installation as a minor modification to a certified aircraft, eliminating the need for a costly supplemental type certificate.