The operation of a Pilatus PC-6 skydiving aircraft's horizontal stabiliser electric trim system will be examined as part of the ATSB's ongoing investigation of a fatal accident near Moruya on the New South Wales South Coast.
A preliminary report, which contains information gathered to date in the ATSB's investigation of the 27 September accident, explains the aircraft had taken off from Moruya Airport shortly before 1400, for a parachute jump flight over the airport, its ninth of the day.
After climbing to the planned jump altitude, recorded data shows the aircraft in a gradual descent from 15,000 ft to 14,000 ft as eight parachutists jumped out. The parachutists later reported the jump was normal, and all exited the aircraft safely.
At 1406:15, the pilot made a radio broadcast on the local CTAF radio that the parachutists had exited and the aircraft was on descent.
"Several witnesses on the ground then observed the aircraft enter a steep nose-down dive, rotating left before pitching up and rolling right," ATSB Chief Commissioner Angus Mitchell said.
The aircraft's last recorded ADS-B data position was at 1407:26, at 7,425 ft and descending at about 15,000 ft per minute.
It collided with terrain about 2.5 km north, and slightly west, of the northern end of Moruya Airport's runway 36. The pilot was fatally injured.
ATSB transport safety investigators' examination of the accident site showed the aircraft's right wing struck a tree on the eastern side of George Bass Drive, and separated from the fuselage, before the aircraft collided with trees on the other side of the road. There was no post-impact fire.
"All major components of the aircraft were at the site, the propeller had indications that the engine was producing power at impact, and there were no indications of any pre-impact mechanical anomalies that would have precluded normal engine operation," Mr Mitchell said.
"Wreckage examination also identified that the aircraft's horizontal stabiliser trim actuator was in the fully nose-down position."
The preliminary report details that the PC-6 is fitted with a horizontal stabiliser electric trim system, which in response to pilot inputs moves the entire horizontal stabiliser to adjust the pitch trim of the aircraft. This reduces the control forces the pilot is required to input on the elevator with the control column.
The report also details the aircraft flight manual's instructions to pilots in the events of trim runaways and jammed trim actuators.
"As the investigation progresses, the ATSB will further examine the horizontal stabiliser trim system, alongside recorded flight data, aircraft history and maintenance records, operational procedures and documentation and pilot training."
Mr Mitchell also said the investigation would consider the configuration of the aircraft's doors, and the pilot's opportunity to egress during the accident sequence.
"Consideration will be given to survivability aspects, given the pilot was almost certainly not in their seat when the collision occurred, and they were wearing their emergency parachute," Mr Mitchell said.
A final report, with findings and the ATSB's analysis to support those findings, will be released at the conclusion of the investigation.
