Edited in January 2022
Why is autorotation management important for safety?
Mismanagement of autorotation is a common fatal accident scenario, both in operational flights and in training flights. One of the objectives of the EASA Rotorcraft Safety Roadmap published in December 2018 is to reduce high-risk training scenarios in flight.
Training on full autorotation is particularly relevant for less experienced pilots and those who fly less forgiving rotorcraft. Some of the lighter helicopters have low rotor inertia, which also make this type of training more risky.
One of the questions that the EASA Rotorcraft Roadmap is asking is whether if the risk of training for a particular failure situation is higher than the risk of suffering that failure in operation, then perhaps we should be thinking about doing less of that type of training in the real helicopter and using simulators more often.
Your first question - Could this training also be carried out in the simulator?
Before moving on to talk about autorotation management itself, if you are considering a training flight involving autorotation, the first thing you should be asking is whether you could achieve the same objectives and outcomes using a simulator. Because crashing in a simulator doesn’t damage the helicopter nor injure or kill occupants, training in a simulator is a much safer option
How you can manage an autorotation if you have to?
In powered flight the rotor drag is overcome by engine power but when the engine fails or is deliberately disengaged some other means is required to maintain the RPM. This is achieved by allowing the helicopter to descend and lowering the collective lever so that the resultant airflow provides the driving force to turn the blades.
When sufficient height is available, the helicopter remains fully manoeuvrable in autorotation.
Know and use the manufacturer Indicated Airspeed and RPM for minimum rate of descent in autorotation and refer to the manufacturer flight manual and procedures.
Entry into Autorotation
- Straight and level cruise, into wind, over a suitable area, and complete airmanship checks
- Lower the collective
- Use throttle to prevent over-speed, as appropriate to type
- When collective is fully down, split needles and select recommended engine RPM
- Prevent yaw
- Control heading and airspeed with cyclic, as in powered flight
- Note: Changes in speed will cause the RPM to increase and decrease; control RPM with the collective
- Note: Turns in autorotation increase the rate of descent and RPM
- Incline the lift vector of the rotor system to the rear slowing forward speed
- Note: Increased airflow results in increasing RPM; control RPM with the collective
- Note: The lifting force of the rotor system is increased and rate of descent is reduced
- Note: The lack of torque is noticeable and the aircraft fuselage may rotate counterclockwise with application of the collective due to frictional drag in the transmission, drive train, associated pumps, and generators (depending on type of helicopter)
- Apply pedal to maintain a heading aligned with the touchdown area
- Note: Any crosswind also causes the nose to weathervane into the wind due to lift produced by the vertical fin
- During this final phase of the autorotation with the airspeed at a minimum, move the cyclic stick forward to place the aircraft in a landing attitude while applying collective pitch to cushion the landing
- Note: The height at which this phase is entered depends on the size of the helicopter and the length of the tail-boom. The landing attitude varies between helicopter designs from touching the aft portion of the landing gear first as in an airplane, to a level attitude with all surfaces touching down at once
- Control heading with the pedals to preclude the aircraft from rolling over when contacting ground
Some of the Most Common Errors
- Allowing the nose to drop during entry
- Allowing aircraft to yaw during entry and re-engagement
- Over controlling on cyclic on entry
- Closing throttle before collective lever is fully down
- Over speeding the engine by not closing the throttle as collective lever is lowered
- Harsh re-engagement with a tendency to over pitch on go-around with low RPM
- Rapid throttle engagement and raising collective lever on go-around causing over-speed
- Ensuring safe air-speed, before initiating go-around, to prevent Vortex Ring State (VRS)
Helicopter Instructor Guides
The three guides listed below provide valuables training guidelines and precautions aimed to develop competencies in trainees and reduce the risk of accidents in autorotation training flights:
- Based on and upgrading the EHEST Helicopter Flight Instructor Manual, the EASA Helicopter Flight Instructor Guide aims to assist instructors implement the PPL(H) Syllabus. Autorotation is addressed in PART II Exercises 10 Basic Autorotation, 14c Emergency procedures, 19 Simulated Engine Out Landing (EOL), 20 Advanced Autorotation and 21 Practice Force Landings.
- FAA Helicopter Instructor’s Handbook, Chapter 3 Aerodynamics of Flight, Chapter 3 Autorotation, and Chapter 12 Helicopter Emergencies.
- CASA Flight Instructor Manual (Helicopter), PART II Ground and Air Instruction Exercises, 13. Entry to autorotation, 14, Power terminated and touchdown autorotations, and 15. Autorotation variables.
This article is based on the EASA Rotorcraft Safety Roadmap, issue 1, Chapter III.3 Training in Flight and EASA Helicopter Flight Instructor Guide, issue 3, PART 2 - Air Exercise. It also refers to the FAA Helicopter Instructor’s Handbook, 2012, and CASA Flight Instructor Manual (Helicopter), issue 3.