What happened
During an approach to a landing site, the pilot of the helicopter experienced a sudden sensation of "no power," which they believed to be an engine failure. During the descent, the airframe separated from the landing skids and rotated 180 degrees. The impact occurred at low forward speed, and the aircraft's landing skids and airframe ended in a position consistent with engine torque being applied to the airframe at low rotor speed. The pilot and passenger survived the crash but were not located by search and rescue services until approximately 39 hours after the event.
The investigation
Investigators examined the wreckage and found no evidence of mechanical faults prior to the impact. While the pilot reported an engine failure, the ATSB noted that the symptoms were more consistent with a rotor stall. In such an event, the engine continues to apply torque to the airframe, which can cause an uncommanded turn and a decay in rotor speed, often perceived by the pilot as a loss of power. The investigation also ruled out fuel exhaustion or fuel starvation as likely causes.
Regarding the aircraft's safety equipment, the pilot had verified the circuit breakers and warning lights before takeoff; the tripped breakers found after the crash were likely caused by impact forces. Additionally, the pilot was using an active noise reduction headset, which may have hindered the ability to hear subtle changes in engine or rotor pitch, though this was not specifically tested.
Findings
- The helicopter was manufactured to 1956 standards and was not fitted with a low rotor speed warning system, a feature required by modern airworthiness standards.
- The pilot likely entered an incipient rotor stall while focused on positioning the aircraft for landing, and the lack of a warning system meant the condition went undetected until it was too late to recover.
- The aircraft was carrying an EPIRB, but because it required manual activation and the pilot could not retrieve it from the wreckage, there was a significant delay in activating search and rescue.
- The absence of an automatically activated ELT and the inaccessible EPIRB increased the risks to the occupants' post-accident survival.