On 9 January 2015, the pilot of a Robinson R44, registered VH-YMD, was operating in support of the Northern Territory Police. As part of the operation, the pilot was asked to convey three passengers from a location on the bed of Todd River just north of Alice Springs, to another site near Alice Springs Township.

The pilot lifted off from the river bed and commenced departure over the river to follow what he assessed to be the most suitable departure route. Lift-off was normal, but as the helicopter climbed away from the river bed the pilot became aware that the main rotor RPM was decaying. In response, he overrode the governor and applied full throttle. The pilot was able to clear rocks and shrubs on the opposite side of the river, but with decaying rotor RPM he was forced to make a run-on landing on a flat area just above the river bed.

The helicopter tipped precariously during the landing. The pilot immediately lifted off again to reposition the helicopter with a level attitude, following which he shut down the engine and the passengers evacuated. The helicopter was substantially damaged during the event, particularly the left skid and the tail boom.

A number of factors related to power available and power required probably explain why the rotor RPM decayed during departure from the river bed. These factors relate to density altitude, take-off weight and possibly a tail wind component. This accident provides a reminder to pilots to carefully and accurately assess these factors before committing to any departure. When performance is likely to be adversely affected by a combination of these factors, extreme caution is warranted.

Aviation Short Investigations Bulletin - Issue 41


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