A firefighting helicopter sustained substantial damage when it unexpectedly lost height when filling its underslung bucket from the Murchison River on Tasmania's West Coast, an ATSB investigation interim report details.
The twin-engine Bell 412 helicopter, operated by Coulson Aviation, was performing waterbombing activities for the Tasmanian Fire Service in the Cradle Mountain-Lake St Clair National Park in the state's west on 10 March 2025.
While hovering at about 150 ft over the Murchison River refilling its bucket, which was attached via a longline, the helicopter sank unexpectedly about 50 ft.
While applying recovery control inputs, the pilot, the sole occupant, unsuccessfully attempted to jettison the longline, and it subsequently became taught.
"The helicopter then came to an abrupt stop and the pilot heard a 'loud clunking noise'," said ATSB Director Transport Safety Dr Stuart Godley.
"The pilot then recovered the helicopter to a stable hover approximately 30 ft above the water and initiated rearward flight to release the water and retrieve the bucket from the river."
The pilot then observed an engine torque split - when the proportion of main rotor torque is spread unevenly between the helicopter's two engines.
"After regaining control and recovering the longline and bucket, the pilot found the tail rotor pedals to be stiff, but said they were still able to control the helicopter."
The pilot subsequently flew the helicopter back to the air base at Zeehan, about 33 km away.
"During this flight, the air attack supervisor - in a different aircraft - observed the helicopter's flight as abnormal: slower and lower than usual, and yawing from side to side," Dr Godley said.
After landing at Zeehan, the pilot was unable to roll the engine throttles back to idle, and had to cut fuel supply to shut the engines down.
A post-flight inspection found substantial damage to the helicopter's fuselage structure aft of the external hook, and damage to the water bucket.
A technical inspection by the operator the following morning found the #1 (left) engine control tube had sheared, resulting in a complete loss of pilot input to that engine, and the #2 (right) engine control tube bell crank attachment bracket had detached, restricting pilot control of that engine.
Dr Godley noted the investigation had so far included interviews with involved parties, and the review of recorded aircraft information, weather conditions, maintenance documentation and pilot training.
"As the investigation progresses towards a final report, it will also review Coulson's risk controls for bucketing operations in the Bell 412, and operational and reporting procedures for both Coulson and the Tasmanian Fire Service," Dr Godley explained.
"A final report will be released at the conclusion of the investigation once the available evidence has been analysed and findings are developed and established."
You can find here the interim report: Loss of control and equipment contact with water involving Bell 412EP, VH-VJF, 57 km north-east of Strahan Airport, Tasmania, on 10 March 2025
