What happened
On the day of the incident, an EC120 helicopter was operating within the Parramatta River helicopter lane. Radar data and pilot reports indicate that the aircraft passed over the Ryde Bridge approximately nine seconds after a heavier, three-bladed helicopter had passed through the same area. During this transit, the pilot experienced sudden, heavy turbulence and an uncontrolled descent. In an attempt to prevent the aircraft from striking the water, the pilot applied full collective, which led to a low rotor speed condition. Consequently, the pilot was forced to perform an emergency landing on the banks of the Parramatta River.
The investigation
Investigators examined the flight path and the aircraft's mechanical state following the event. While the aircraft was flying in relatively calm wind conditions, the investigation focused on the proximity between the two aircraft. Analysis of primary radar data confirmed that the aircraft was flying slightly below and behind the preceding heavier helicopter. Post-incident maintenance inspections were conducted on the EC120, but no mechanical faults or defects were identified, and the aircraft was found to be in a serviceable condition for flight.
Findings
- The aircraft entered the rotor wake produced by a preceding, heavier three-bladed helicopter.
- This encounter with rotor wake turbulence triggered the uncontrolled descent and subsequent control difficulties.
- The application of full collective to avoid the water resulted in a low rotor speed warning.
- There were no mechanical failures found during subsequent inspections of the aircraft.