On September 4, 2024, a Royal Navy Merlin Mk4 helicopter crashed into the English Channel during a night training exercise involving the HMS Queen Elizabeth. The accident resulted in the death of 31-year-old Lieutenant Rhodri Leyshon after the crew mistakenly deactivated functioning engines.
The Safran diaphragm failure and the 136 percent torque surge
The sequence of events began with a mechanical failure in the fuel system of the No. 2 engine, specifically a ruptured rubber diaphragm. According to a 152-page report by the Defence Safety Authority, this rupture caused a sudden fuel flow surge that pushed the engine's torque output beyond 136 percent. To compensate and maintain rotor speed, the Merlin Mk4's automatic turbine control reduced power to the other two healthy engines.
This mechanical trigger points to a broader systemic risk within the fleet. Maintenance investigators traced the faulty diaphragm to a design introduced by the manufacturer Safran in 2020. as the Defence Safety Authority report noted, ten out of 117 suspect diaphragms examined after the crash showed potentially dangerous damage, suggesting that other aircraft with the same configuration may be at risk.
Confusing 'ENG FAIL' alerts and the 21-second window of error
The mechanical fault created a cockpit environment characterized by ambiguity. The crew was met with a master warning and a red "ENG FAIL" indicator that failed to specify which of the three engines was actually malfunctioning. Because the automatic system had lowered the power of the healthy engines, the crew misinterpreted the lower torque readings as evidence that engines one and three had failed.
The breakdown in communication happened rapidly; within 21 seconds of the initial fault, Lieutenant Rhodri Leyshon informed the crew that the helicopter was operating on a single engine. This diagnosis was not challenged by the commander.. Roughly one minute into the emergency, the commander shut down engines one and three by moving switches from "FLIGHT" to "OFF," bypassing the mandatory second-crew-member confirmation. This left the Merlin Mk4 dependent on the already-faulty No. 2 engine, which soon hit its overspeed limit and shut down automatically.
Skill fade and the commander's sub-15-hour monthly flight average
The investigation highlights a critical lapse in personnel readiness, describing a collective "skill fade" that impaired the crew's emergency management. The commander, who held the authority for flight-control decisions, was not current for night-vision deck landings. Furthermore, the commander's flight hours over the preceding four months had fallen below the required 15 hours per month, and he had flown only once in the 40 days leading up to the crash.
This lack of currency reflects a worrying trend in high-stakes military aviation where procedural lapses often mirror gaps in active flight time. The Defence Safety Authority report emphasized that the crew worked in relative isolation, failing to collaboratively challenge the incorrect diagnosis of the engine failures, which likely exacerbated the impact of the commander's degraded proficiency.
Incorrect seat weight settings and the failure of two flotation bags
Even after the aircraft struck the sea at roughly 62 knots, safety equipment failed to provide maximum protection.. The energy-absorbing seat used by Lieutenant Rhodri Leyshon had been configured for a weight lower than his actual flight weight, which the report suggests reduced the seat's ability to absorb the 10 g impact forces. Additionally, only two of the four rear flotation bags deployed as intended, compromising the buoyancy of the fuselage after it overturned.
Several critical questions remain regarding the oversight of these safety protocols. It is unclear why the seat weight was incorrectly set or why the flotation system experienced a 50 percent failure rate. Furthermore, while the report identifies the Safran diaphragm as a point of failure, it remains to be seen how quickly the Royal Navy can implement the recommended overhaul of crash-protection systems and maintenance procedures across the entire Merlin Mk4 fleet.
Comments 0