A sightseeing helicopter accident as a result of a seized bearing demonstrates the importance of ensuring all aircraft parts are maintained in accordance with regulations and manufacturer guidance, an Australian Transport Safety Bureau investigation report highlights.
The Robinson R44 helicopter was being used for a sightseeing flight over Limmen National Park, NT on 16 May 2022, with a pilot and three passengers on board.
During cruise, the pilot detected vibrations and observed the engine RPM rise and then drop to zero. In response, the pilot initiated an autorotation, flaring above trees before the helicopter contacted the ground initially on the right front side, nose low. The helicopter then spun and rolled on to the left side facing the opposite way to the direction of travel.
Two of the passengers were seriously injured in the accident, while the pilot and other passenger sustained minor injuries.
An investigation by the ATSB found the helicopter’s clutch actuator lower bearing had seized, resulting in a total loss of drive from the engine to the rotor system.
“Two key findings from this investigation demonstrate the importance of following the relevant manufacturer’s maintenance procedures for all components of an aircraft,” ATSB Director Transport Safety Stuart Macleod said.
The ATSB found the seized bearing had not been maintained in accordance with the maintenance procedures.
Early in its life, the bearing had been lubricated less often than the 300 hour frequency stated in Robinson’s guidance. More recently, the maintenance organisation advised the bearing was lubricated more frequently than required.
“If a maintainer considers that additional maintenance should be conducted on any component of an aircraft, they should contact the manufacturer for engineering advice before varying from the procedure,” Mr Macleod said.
Additionally, the helicopter’s emergency locator transmitter (ELT) did not activate during the accident sequence.
The maintenance organisation advised they had not maintained the ELT since taking over maintenance of the helicopter. The operator stated they presumed it was being maintained on a 100-hourly basis.
“This serves as a reminder to operators that they should be ensuring a self-test of the ELT unit is conducted monthly, to verify it is operational.”
The report also notes findings relating to the absence of a pre-flight safety briefing, and the lack of clear guidance from the Civil Aviation Safety Authority (CASA) about brace positions for helicopters with 3-point harnesses.
“CASA has since the accident released a revised multi-part advisory circular to include information on how to brace in a helicopter with a 3-point harness,” Mr Macleod said.