A main KAflex drive shaft failure led to the fatal crash of a firebombing Garlick UH-1H helicopter in Tasmania, according to an ATSB investigation report released this week.
VH-UHX was tasked to support the Tasmania Fire Service on a bushfire at Lebrina north-east of Launceston in February 2022, when the pilot lost partial drive to the rotor system. The pilot dumped the load of water and headed towards clear ground, but the aircraft then suffered a total loss of drive.
The pilot was not able to complete a safe autorotation–possibly due to a loss of main rotor speed–and the aircraft collided with the ground. The pilot suffered fatal injuries.
The investigation found that the helicopter’s engine-to-transmission main KAflex drive shaft partially failed due to fracture of a flex frame attaching bolt, or a flex frame element and entered fail-safe mode.
During its investigation, the ATSB issued a safety advisory notice to all UH-1H operators with details of the accident and to look for defects in the KAflex drive shaft of their helicopters, if fitted.
Also since the accident, CASA has updated a previously-released AWB on the subject of pre-flight inspection requirements for the KAflex drive shaft.
The US FAA now requires operators to replace KAflex drive shafts beyond 5000 hours of use, or where flight hours are unable to be verified.
“A rapid increase in vibration or noise from the transmission area – significantly the commencement of a distinct ‘howling’ or ‘shrieking’ – may signify the KAflex has entered fail-safe mode, and could imminently fail,” said ATSB Chief Commissioner Angus Macleod said.
“Pilots should land as soon as possible on detection of such symptoms.”
The full investigation report is on the ATSB website.