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Autorotation Fly-Through | A Potentially Dangerous Compromise

Posted 3 years 1 days ago ago by Randy Rowles

An increasing number of helicopter flight schools have reduced emphasis on the flare portion of the autorotation due to over-speeding. I’m told the risks of an over-speed outweigh the benefit the student experiences by conducting a positive flare in the early stages of autorotation training. It seems consensus among helicopter flight school leadership is that a gentle reduction in forward velocity to an approximate 30-knot ground speed is enough, and a go-around from this point in the maneuver is the safest solution. To be very clear, this is a dangerous compromise!

The flare portion of the autorotative profile is a key component to the survival of this maneuver. The understanding and ability of the pilot to position the helicopter correctly so that a safe landing can be accomplished is the goal. Leaving a large amount of energy available in the airspeed of the helicopter is a critical mistake. The assumption that every autorotation will end with a long, hard, smooth surface is more fantasy than fact.   

The profile of the glide dictates the aggressiveness of the flare in many cases. A high-speed, low rotor RPM extended glide autorotative profile will begin with a small amount of aft cyclic to engage a deceleration without an altitude increase. However, the airspeed will begin to reduce rapidly. When this occurs, an increase in the flare profile will allow the helicopter to maintain a low constant altitude above the ground while sustaining rotor rpm. We see this profile often flown at airports with long, low flares to the predetermined point of touchdown. This may not be the suggested profile in an actual emergency autorotation as the low altitude of the flare is well within the expected obstacle height to include wires, trees, etc.

A smaller open area two or three times the main rotor diameter of the helicopter is likely a realistic emergency landing area. In these cases, a slower (minimum rate of descent) type autorotation may be better suited. The desired rotor RPM may vary based on the phase of the maneuver. Lower rotor RPM during the glide will provide a slower rate of descent. However, increasing rotor RPM toward the end of the autorotation may aid the flare due to the lower airspeed, which may affect positive energy transfer. In either case, the rotor RPM at the end of the flare will directly affect aircraft controllability and ground run.    

I reference airspeed, but ground speed is more important when the skids touch the surface. The airspeed is key for a helicopter to have a functional flare. Once the flare begins and the transfer from horizontal flight to ground contact occurs, the importance shifts to ground speed. Having a high ground speed when confronted with a marshy area, a busy city street, or a small landing area will most likely be disastrous. 

Training autorotations to fly through the flare portion of the maneuver should be a technique utilized when the maneuver is in jeopardy, or when a go-around is the safest course of action. Using this technique to increase the number of autorotations during a single training evolution is common among helicopter flight instructors and may create a potentially hazardous motor-skill for the student.

The intent of the performance-based autorotation on the practical test is to measure the applicant’s ability to maneuver the helicopter to within a specified distance from a predetermined spot. Flying thru the autorotational flare in training may cause the applicant to be found unsatisfactory during the practical exam, and a compromised flare during an actual  emergency autorotation may find you sharing space with the same obstacle you tried to avoid!    

About Randy:  Randy Rowles has been a FAA pilot examiner for 20 years for all helicopter certificates and ratings. He holds a FAA Gold Seal Flight Instructor Certificate, NAFI Master Flight Instructor designation, and was the 2013 recipient of the HAI Flight Instructor of the Year Award. Rowles is the owner/president of Helicopter Institute.