An unexplained loss of engine power led to a loss of control and the fatal crash of a Robinson R22 according to an ATSB investigation report released last week.
VH-PSC was on mustering operations in company with a second R22 near Limbunya Station in the NT in June last year when the mustering crew lost contact with the pilot. The pilot of the second R22 conducted a short search before locating the wreckage of PSC in a moderately treed area, which had no powerlines in the vicinity. The aircraft was destroyed, and the pilot died in the crash.
ATSB investigators attending the crash site found the both main rotor blades remained connected to the rotor head all components associated with the rotor head, blades and flight controls were secure and the pitch links were secured to the swashplate and main rotor pitch horns.
One pitch horn showed distortion consistent with a ground strike and the only damage to the rotor blades was backward bending.
The ATSB said that these characteristics were consistent with the engine not driving the rotor blades at the time of impact, but couldn't explain why.
“The site and wreckage signatures were consistent with the helicopter being in a low rotor energy state with low-to-nil engine power,” Director Transport Safety Kerri Hughes said.
“Investigators were able to confirm continuity of the flight controls prior to the accident, while an examination of the helicopter’s engine found no damage or defects that may have affected its pre-accident operation.”
ATSB investigators considered the possibility of pilot incapacitation, but a review of the pilot’s medical history and post-mortem examination results there was insufficient evidence to determine if the pilot became incapacitated.
“Therefore, in the absence of an identified problem with the helicopter and having considered other plausible explanations, the reason for the engine reduction and loss of control could not be determined," Hughes said.
Investigators found no mechanical issues with the engine or other systems, and there was no evidence found of birdstrike, wirestrike or mast bumping.
Crash distortion prevented investigators determining the throttle position at impact, although the mixture control was found in the full rich position.
"Therefore, due to the limited evidence available, the ATSB was unable to determine the reason for the engine power reduction and loss of control, nor the sequence of these events," the report says.
The full report is on the ATSB website.