Angle of Attack and Your Airplane

Angle of attack, despite sounding a bit dramatic, is defined as the acute angle between the chord line of the airfoil and the direction of the relative wind. In a high angle of attack situation, the wing of an airplane begins to lose lift and in some cases, can potentially stall. Failure to recognize this while in flight can result in an abrupt loss of altitude and if not handled properly, loss of aircraft control. I know you might be thinking, “Isn’t this a bit technical for a Friday?” But bear with me!

More commonly seen on military and commercial aircraft, Angle of Attack (AOA) indicators are now becoming the topic of conversation among general aviation. The FAA recently announced in February that it is going to make the installation of angle of attack indicators in GA aircraft easier, so what are you doing to take advantage of this safety-enhancing opportunity? 

The Garmin AOA system was announced several months ago and is comprised of the GI 260 AOA indicator, GAP 26 probe and GSU 25 air data computer. Pitot and AOA pressure is sensed using the GAP 26 and is combined with other parameters in the GSU 25 air data computer, where “normalized” AOA is computed. “Normalized” AOA is unique in that it provides a consistent indication of AOA irrespective of atmospheric conditions, providing a much more accurate readout of the amount of lift remaining.  The Garmin AOA system combines pressure differential between two ports on the pitot and computes the effects of weight, G-loading and density altitude, therefore offering a “normalized” value, which yields true AOA.

What’s the difference between a so-called Lift Reserve Indicator and an AOA indicator? A lift reserve computer uses the difference in pressure between two ports on a pitot probe that is calibrated and used to determine “Lift Reserve.” However, this pressure differential can change with aircraft weight, G-loading, density altitude and more. If any of these conditions differ from the calibration settings, the indication may not be correct and therefore not yield true AOA.

Angle of attack indicators can provide a number of benefits and act as a great supplement to airspeed indicators and stall warning systems. Thanks to the FAA’s simplified installation approval, pilots can easily and affordably put an AOA system in their airplane and add yet another safety-enhancing tool to their cockpit.

So, what are you waiting for?

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