Introduction
The initial video uploaded by SleepyTito discusses the impact of aircraft icing on the horizontal stabilizer and its link to numerous turboprop accidents. Ice accumulation on the horizontal stabilizer can lead to sudden nose pitch-downs or other severe control problems, particularly when flaps are extended (SleepyTito, 2009a).
Discussion
Regional airline fleets flying at lower altitudes in icing-prone environments are particularly susceptible to such issues, but both small and large general aviation aircraft can experience tail plane icing. However, despite the prevalence of such incidents, the procedures for handling tailplane icing still need to be clarified, and traditional techniques for wing stall recovery may even exacerbate the problem. The video mentions NASA’s ongoing research and training efforts, including the comprehensive study by the NASA Lewis Research Center, whose findings will be used by regulatory authorities and aircraft manufacturers (SleepyTito, 2009a). It is crucial for pilots to be aware of the symptoms of tailplane icing and to be prepared to take corrective action to prevent an ice-induced tailplane stall. Proper procedures and knowledge can prevent tragic accidents from pilot errors.
SleepyTito’s second video explores the basic principles of aerodynamics in straight and level flight. The video shows that the wing’s center of lift moves when flaps are extended, causing the horizontal stabilizer to compensate for a perfect nose-down pitching moment (SleepyTito, 2009b). If the aircraft slows down, the extension of flaps brings the horizontal stabilizer closer to its stalling angle, making tailplane icing a significant issue. A small amount of ice on the tailplane leading edge can disrupt the airflow on the lower surface of the horizontal stabilizer, causing flow separation that reduces the stalling angle of attack and limits the amount of negative lift available. NASA conducted flight tests to measure the aerodynamic effects and control characteristics of tailplanes contaminated with ice (SleepyTito, 2009b). The tests discovered three factors that could result in tail stall conditions: increasing flaps, speed, and power. The video features accurate in-flight maneuvers, Tuft and instrumentation data, and visual cues that warn of possible tailplane stall conditions (SleepyTito, 2009b). However, intentional tailplane stall maneuvers are not recommended in an uncontrolled environment. Video warns against intentional tailplane stall maneuvers in a wild environment.
In the third video from SleepyTito, NASA showcases the testing of tailplane icing on a modified de Havilland DH6 aircraft by attaching polyurethane ice castings to the horizontal stabilizer. The research showed that an ice-induced tail stall could occur through three paths: increasing flaps, speed, and power (SleepyTito, 2009c). If a tail stall is detected, the pilot should immediately retract the flaps, pull the yoke back, and use power judiciously. The pilot should differentiate between an airframe buffet and a yoke buffet, with the latter providing feedback through the seat of their pants. If the aircraft is equipped with a de-icing system, the pilot should activate it several times to clear ice. Avoiding autopilot in known icing conditions and retracting flaps to the previous setting if lightning of the controls, difficulty in trimming, or pilot-induced oscillations are experienced can prevent ice-induced tailplane stalls (SleepyTito, 2009c).
Conclusion
The aviator should make pitch changes slowly, avoid full extension of flaps, and consider landing with reduced flaps. Large aircraft with hydraulic controls have subtler clues, including unusual trim settings and the possibility of pilot-induced oscillations..
References
SleepyTito. (2009a). 1 of 3, aircraft icing loss of control [Video]. YouTube. Web.
SleepyTito. (2009b). 2 of 3, aircraft icing loss of control [Video]. YouTube. Web.
SleepyTito. (2009c). 3 of 3, aircraft icing loss of control [Video]. YouTube. Web.