The “catastrophic, but contained failure” of an Australian army NH Industries (NHI) MRH90 Taipan transport helicopter’s left-hand Safran Helicopter Engines RTM322 led to it ditching during a non-fatal training accident last year.
Australian defence minister Richard Marles on 13 September released a redacted version of an aviation safety investigation report into the 22 March 2023 event, in response to a request from minister for emergency management Senator Jenny McAllister.
Operating as ‘Bushman 82’, the twin-engined rotorcraft lost power when a blade in its high-pressure turbine’s high-pressure 1 (HP1) wheel ruptured while its crew was performing an overwater helicopter insertion and extraction technique manoeuvre at night with special forces divers suspended from either side of its fuselage.
Australia’s Department of Defence had previously confirmed that four crew members and six passengers were involved – all escaped serious injury.
Following the sudden power loss, incident aircraft A40-025 descended and briefly made contact with the water, before its right-hand engine automatically reached its maximum available one engine inoperative power rating.
“The aircraft then rose into a low hover of approximately 23ft, albeit with rotor speed decaying,” the report says.
During this time, “the non-flying pilot in the left-hand cockpit seat, believing the aircraft had settled on the water, removed their helmet in preparation for commencing emergency egress procedures”. The crew member perceived that the MRH90 “would roll inverted, and snagging hazards related to the [Thales] TopOwl [helmet-mounted display] quick-release pack, and associated helmet leads, would prevent underwater egress from the cockpit”.
Meanwhile, the pilot flying chose to switch off the still operational right-hand RTM322 while at a height of around 19ft: “not in accordance with standard emergency procedures”.
“This resulted in a high rate of decent, an impact force of 8g, extensive structural damage to the airframe and automatic activation of the emergency flotation system,” investigators say.
“This decision was found to be heavily influenced by their concern over potential injuries to the crew and personnel in the vicinity caused by flying debris from high-energy rotors striking the water,” they add.
The aircraft’s rear left-hand aircrewman had jettisoned the divers on their side of the aircraft, but their colleague on the other side had been unable to do the same while using night-vision goggles. This resulted in some divers “being dragged unexpectedly through the water… which resulted in the forced removal and/or degradation of underwater breathing equipment”.
Despite the hard impact, the 6th Aviation Regiment-operated aircraft remained “upright and afloat” on the shore of Jervis Bay, New South Wales.
“The crew was not expecting, nor were prepared for, a scenario where the flotation system kept the aircraft afloat and upright,” the report says.
While the engine blade failure was the first such event to have affected an Australian MRH90, NHI had in 2017 issued a service bulletin to operators of RTM322-powered NH90s following “several HP1 failures across the global fleet”. This advised them to replace the affected part with a redesigned version.
Neither of A40-025’s installed engines had yet received the enhancement, since the Australian army had decided to install replacement blades as part of scheduled depth-level maintenance activities. Cirium fleets data shows that the incident aircraft had entered service in November 2013.
The report makes 13 recommendations, mainly around “organisational-level policy, processes, standardisation and training, as well as the efficacy of aviation risk management”.
Canberra permanently withdrew its remaining fleet of more than 40 MRH90s from use after another of its aircraft crashed in the sea off Queensland in July 2023, killing all four crew members.
The Australian army is in the process of acquiring 40 Sikorsky UH-60M Black Hawks as replacements, with Cirium showing that eight of these as now in operational use.
