One of the most critical maneuvers that helicopter CFIs perform with their students is autorotations. It requires precision, timing and the ability to multitask. Rotor RPM, airspeed and trim must all be maintained within allowed parameters while simultaneously finding a suitable landing area and maneuvering the helicopter into the wind. From 500 feet above ground level, a student has 20 to 30 seconds to process and manage all the factors and make the right decisions to achieve a successful outcome.
Allowing a student to perform an autorotation requires constant vigilance from the instructor. The best way for students to learn is by doing as much of the maneuver as possible, however, the instructor does not always have a lot of time to decide to take the controls before the student gets the helicopter in an unrecoverable situation. Sometimes, the difference between a successful practice autorotation and an accident is just a second or two.
During the first 2 months of 2012 three accidents happened from practice autorotations and the NTSB issued the following probable causes:
- The flight instructor’s delayed remedial action during the pilot-receiving-instruction’s practice autorotation that developed a high rate of descent. Contributing to the accident was the pilot-receiving-instruction’s improper control inputs during the practice autorotation.
- The flight instructor’s failure to apply power during a practice autorotation in order to arrest a high rate of descent, which resulted in an in-flight collision with terrain.
These two happened in a Robinson R22 and a R44. However, the following is from an AS350 with a more experienced instructor.
- The flight instructor’s improper use of the collective control during a practice hovering autorotation, which resulted in a hard landing.
Even an excellent and experienced instructor who gets distracted, even for just a second or less, can damage an aircraft. Full touchdown autorotations (that is, not bringing the engine back in before ground contact) add another level of risk. Fortunately, most accidents that happen from practice autorotations are not fatal.
NTSB accident references:
NTSB Identification: WPR12TA120
NTSB Identification: ERA12CA179
NTSB Identification: ERA12CA137