ATSB warns of the risks surrounding practice autorotations

ATSB warns of the risks surrounding practice autorotations

15-Nov-2012 Source: ATSB

As a result of the ATSB investigation and in order to reduce the level of risk associated with emergency training, a helicopter operator is investigating amendments to their company operations manual.

One amendment being investigated by the operator is the requirement for at least 10 kts of wind in the runway direction for the performance of low-level practice operations. This is an important safety action, as ATSB research indicates that for helicopters the greatest risk of an accident occurs during the performance of practice autorotations.

The accident occurred on 18 June, 2012, when an instructor and student were conducting emergency procedures training in the circuit at Redcliffe aerodrome in Queensland. They were flying in a Schweizer 269C-1 helicopter and, as part of a bi-annual flight review, were carrying out low-level autorotations to simulate an engine failure on approach. (Autorotation occurs during descent with the power off. The air flowing in reverse direction upwards through the lifting rotor(s) causes it to continue to rotate at approximately cruise RPM.)

When the helicopter was at about 250 ft above ground level and 55 kts airspeed, the instructor called for a practice engine failure. The student closed the throttle and lowered the collective to enter autorotation. Power was restored shortly after, by opening the throttle in anticipation of a power termination. The student flared the helicopter, however the helicopter did not decelerate as expected. The instructor increased the flare in an attempt to arrest the rate of descent and decrease the groundspeed.

The tail rotor struck the ground and the helicopter pitched forward. The crew closed the throttle in an attempt to recover from an uncommanded right yaw, however the helicopter impacted the ground before the rotation could be arrested and the helicopter rolled over. The helicopter was seriously damaged. Both instructor and student reported soft tissue injuries and some minor cuts and bruises.

The reason for the accident could not be conclusively established, however it was considered likely that the helicopter encountered low level wind shear during the flare resulting in a tail rotor strike and subsequent loss of control.

When performing autorotations, there are a number of factors that must be considered in planning and execution to achieve a successful outcome. The investigation report AO-2012-082 includes important advice, and also provides links to other useful sources of information on the subject.

You can find this and other investigations in the ATSB’s Aviation Short Investigation Bulletin issue 12. The bulletin highlights valuable safety lessons for pilots, operators and safety managers.

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