Flight Testing Angle-of-Attack Warning Combinations on Part 23 Aircraft
Geehan, Jennifer Grey
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The high number of accidents involving General Aviation (GA) aircraft leads to a need for improved methods to warn pilots of high angles of attack (AOA) and impending stall. Such methods must be certified by the Federal Aviation Administration (FAA) under Federal Aviation Regulations Part 23 regarding their effectiveness in preventing departures from controlled flight. Therefore, methods of compliance must be developed to certify Part 23 aircraft equipped with AOA warning or limiting systems. The research objectives were to (a) determine methods for the evaluation of AOA warning and limiting systems and to (b) evaluate the effectiveness of baseline combinations of such systems. The warning systems included visual, aural, and haptic feedback cues. The work performed in this study was the design, implementation, and testing of an AOA indicator that intuitively displayed the aircraft’s AOA and its current flap configuration. Also tested were aural alerts that informed the pilot of both the state of the aircraft and the actions needed to prevent further energy decay. Finally, an active stick that provided haptic feedback by shaking, pushing, and stepwise increasing the stick force depending on AOA was tested. These systems were evaluated using both a traditional stall matrix approach and an innovative AOA tracking task. The test aircraft used was the Technical University of Munich’s fly-by-wire DA42. The key results were that the stall matrix was found to be an effective means to establish compliance, while the AOA tracking task did not produce the desired repeatability and consistency and could potentially be unsafe. However, the tracking task was effective in monopolizing pilot awareness and this lack of situational awareness is believed to be a major cause in fatal GA accidents. From the visual, aural, and haptic feedback cues evaluated, all evaluation pilots preferred the AOA indicator developed for the project over current off-the-shelf products, the human recorded voice was the preferred aural alert, and the stick shaker was found to be very effective. The stick pusher, the only active system tested, needs further investigation for safe operation at low altitudes.