The Australian Transport Safety Bureau’s investigation into the in-flight breakup of a Robinson R44 helicopter at Broome, Western Australia on 4 July 2020 is continuing.
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A preliminary report from the on-going investigation details that the helicopter, with a pilot and three passengers on board, had departed a yard in the Broome industrial suburb of Bilingurr for a private local scenic flight.
As the helicopter reached a height of about 55 feet, witnesses heard a bang, which one described as sounding similar to a metal bar striking a metal pole. Footage from a nearby CCTV camera showed that the R44’s aft tail cone bulkhead, empennage, tail rotor gearbox and tail rotor assembly all separated from the helicopter in about one second.
The helicopter climbed to around 75 feet while rotating rapidly to the right, before rolling and impacting the ground on its right side, about 30 metres from the departure point.
The pilot, who owned the helicopter, and a passenger, both seated on the right side of the helicopter, were fatally injured, while the front left seat and rear left seat passengers were seriously injured. The helicopter was destroyed.
“ATSB preliminary reports detail factual information established in the investigation’s early evidence collection phase, and contain no analysis or findings, which will be detailed in the investigation’s final report,†ATSB Director Transport Safety Dr Mike Walker noted.
The preliminary report details that on 29 June the R44 was ferried from Bilingurr to Broome Airport, where it was fitted with a tracking system.
“That pilot reported feeling a vibration in the tail rotor pedals that felt like someone tapping the pilot’s feet with spoons. The sensation was noticeable yet not strong enough to cause significant alarm.â€
Three days later the helicopter’s owner, accompanied by a passenger, returned the helicopter to Bilingurr, where on landing the owner also reported feeling vibrations in the pedals, and requested maintenance engineers inspect the helicopter.
Subsequently on 3 July, a maintenance engineer visually inspected the R44’s flex plate, empennage, gearbox, pitch links and tail rotor assembly, and found no defects.
In addition, the maintenance engineer and an apprentice used electronic dynamic balancing equipment to measure the dynamic balance of the tail rotor, which was found to be within limits.
A maintenance pilot started the helicopter, and while ground running the R44 could not feel any vibration through the pedals. In addition, the maintenance engineer leant into the cabin and placed their hands on the pedals, and also could not feel any vibration.
Due to the confined nature of the yard, and concerns over securing the site, the maintenance pilot elected not to test fly the helicopter, and so the tail rotor system was not assessed under load.
The maintenance pilot stated separately advising the pilot who originally detected the vibration and the owner that the engineers had not detected a vibration, and that the tail rotor was in balance.
The maintenance pilot also stated that the owner was told that no changes were made to the balance weights, that the helicopter had not been flown, and that an instruction from the engineer to conduct a check flight was relayed.
The accident flight was conducted the following day, with the helicopter owner as the pilot.
“It is not clear whether the pilot experienced any vibrations through the pedals at the time of the accident flight,†Dr Walker said.
“Nevertheless, the ATSB urges any R44 pilot who experiences unusual vibrations through the tail rotor pedals to land as soon as possible and follow the advice in the pilot’s operating handbook.â€
The R44 pilot’s operating handbook advises that a “change in the sound or vibration of the helicopter may indicate an impending failure of a critical component. If unusual sound or vibration begins in flight, make a safe landing and have the aircraft thoroughly inspected before flight is resumedâ€.
A number of major components from the R44 were recovered to the ATSB’s technical facilities in Canberra for further analysis, including the tail rotor assembly, gearbox, vertical fin and rear section of the tail cone.
“No definitive results from our examinations are available at this stage, and a non-destructive 3D X-ray of the tail rotor gearbox prior to its disassembly did not find evidence of internal damage,†Dr Walker said.
“The ATSB will continue to extensively examine and analyse the recovered components as it seeks to determine the contributing factors behind the in-flight break-up.â€
As the investigation continues, the ATSB will examine a range of aspects.
“These include the on-going, detailed technical examination of the helicopter’s tail and tail rotor assembly; continued review of the accident helicopter’s construction, assembly, flight and maintenance history; and further analysis of the CCTV footage,†Dr Walker said.
The ATSB will also review policies and procedures for maintenance check flights, and examine related occurrences involving the R44.
“While the investigation is continuing, should a critical safety issue be identified at any time, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.†■