Incident Summary
On 3 November 2022, a Robinson Helicopter Company R44 Raven I, registered VH-OCL, departed a cultural heritage site in the Collier Ranges, Western Australia, with one pilot and three passengers on board. During the take-off, just above treetop height and at a speed of about 27 knots, the pilot experienced a severe drop in helicopter performance and the low rotor RPM warning horn sounded. The pilot conducted low rotor RPM recovery actions but was unable to arrest the descent. The helicopter collided with terrain and rolled onto its left side about 150–200 metres from its take-off point. The pilot and two passengers received minor injuries; one passenger received serious injuries. The helicopter was substantially damaged.
ATSB Findings
The Australian Transport Safety Bureau (ATSB) found that the helicopter was operating at a high density altitude. Although the pilot expected to be near but below the maximum gross weight, the helicopter was likely to have exceeded it. This resulted from the pilot not obtaining actual passenger weights, instead using estimated figures not directly provided by the passengers. The pilot had completed performance calculations prior to the day’s flying but did not review or recalculate using actual conditions at the time of the accident flight.
Weight and Balance Issues
The pilot used estimated passenger weights based on physical description rather than weighing or asking for self-reported weights. This approach was very likely to produce an incorrect gross weight. ATSB analysis found the take-off weight was likely about 30 kg more than the pilot calculated, exceeding the out of ground effect (OGE) hover performance weight and the maximum gross weight. Operations above maximum gross weight negate safety margins available to minimise risk of performance-limited conditions.
Performance and Take-off Profile
The pilot believed that lacking OGE performance would prevent high-power, high-performance take-offs. The landing area was confined, with a tree line about 10 feet high blocking the most into-wind direction. The pilot had successfully departed twice that morning with lower temperatures and reduced weight (no passengers). The accident flight was the first departure with a full passenger load and occurred later in the day with higher outside air temperature. The pilot did not follow Robinson Helicopter Company guidance for clearing an obstacle during take-off; instead of the maximum performance take-off procedure (applying maximum power, climbing vertically to obstacle clearance height before forward flight), the pilot commenced a normal take-off with reduced time in ground effect. The pilot assessed negligible OGE performance and avoided high-power manoeuvres.
Recovery Actions
The pilot initially did not mention increasing throttle when attempting to recover from low rotor RPM, later clarifying they simultaneously lowered collective and rolled on throttle. They reported attempting to increase airspeed (forward cyclic), stating that aft cyclic would slow the aircraft and cause loss of translational lift. This differed from the Pilot Operating Handbook (POH) procedure: “lower collective, roll throttle on and, in forward flight, apply aft cyclic.” The ATSB found insufficient evidence to ascertain the effect of the emergency technique, but not applying the correct recovery may have inhibited recovery. Given low height, low airspeed, and low rotor RPM, the helicopter lacked sufficient energy to arrest the descent.
Subsequent Actions
The operator immediately paused operations for debriefing and discussions with all company pilots. They engaged an independent auditor to review operations. Prior to the following year’s operations, the operator conducted induction and familiarisation training, including an independent examiner for proficiency checks and flight reviews. The operator stated that passenger-carrying operations would require head of operations clearance to proceed.