Engine fault and switch off of wrong engines led to crash that killed Royal Navy pilot, report concludes
A helicopter crash that led to the death of a Royal Navy pilot was caused by an engine fault that was mis-diagnosed by the crew, leading to two healthy engines being switched off, a service inquiry has found.
Lieutenant Rhodri Leyshon died on 4 September 2024 when the Merlin Mk4 he was piloting came down during a night-flying training exercise with HMS Queen Elizabeth and ditched into the sea. He was recovered from the water roughly two hours later.
An investigation by the Defence Safety Authority (DSA) identified a chain of interconnected failures following the engine malfunction, including issues relating to warning systems, emergency diagnosis, training and operational decision-making.
The lead-up to events
The crew of the Merlin Mk4 had been conducting night-time landings on HMS Queen Elizabeth, approximately 25 nautical miles south of Lyme Regis, Dorset.
On the final approach, while flying at 125ft and 65 knots, a rubber-type diaphragm inside the No. 2 engine ruptured.
Air Marshal AK Gillespie, Director General of the Defence Safety Authority, said: "This allowed fuel to flow through the diaphragm and into the engine. The excess fuel caused the engine to operate at a much faster speed than normal... The split in the diaphragm was the first causal factor."
The rupture caused a red engine fail light to appear to the crew, but this was mistakenly interpreted as indicating the other two engines (No.1 and No.3) had failed and these were manually switched off.
With no power coming from the two engines, and the runaway No.2 engine's own safety system automatically cutting its fuel supply (having hit its own overspeed limit), the aircraft was left without power from any of its three engines.
The helicopter subsequently ditched into the sea nose-up at nearly 10G of force.
Lt Leyshon suffered serious injuries and could not escape as the aircraft broke apart and sank. The other two crew members survived with minor injuries.
Factors and recommendations
The report by DSA categorised accident factors into five groups: causal, contributory, aggravating, other factors and observations.
Casual factors carry the most significance, as removing any one of them would have prevented the accident occurring in the first place. Three were identified in the report.
Mechanical fault
The inquiry found that the diaphragm failure was caused by a manufacturing process at the engine manufacturer, Safran Helicopter Engines, where repeated and excessive pressure had been applied to the diaphragms during assembly – a procedure that had never been through a proper safety approval process.
The report recommends an audit of Safran's UK maintenance and design-approval processes. We’ve asked Safran Helicopter Engines for a statement.
Wrong diagnosis
The crew misread the warnings and concluded the wrong engines had failed.
The inquiry concluded that each crew member was working things out largely on their own rather than together, and no one identified the mistake.
Switching off engines No.1 and No.3
Due to a misdiagnosis, the crew shut off two healthy engines, leading to a total loss of power.
Navy and family reacts
The panel made a total of 44 recommendations, which a Royal Navy spokesman said have been accepted in full. A number have been implemented to date, and they are working to deliver the rest to improve safety for serving personnel.
They added: "Our thoughts remain with Lt Rhodri Leyshon's family, friends, and colleagues at this very difficult time. He served with great professionalism and is much missed by those who knew and worked alongside him."
Responding to the inquiry, the family of Lt Leyshon released a statement via lawyers which said: "The Service Enquiry tells a harrowing story of compounded errors, with numerous mistakes which resulted in this deadly accident."
It added that each of those mistakes were avoidable and set out hopes that processes can be put in place to prevent any similar accident in the future.
Lt Leyshon’s mother Mary said: "I know that he would have done everything within his power to get the helicopter back. It is therefore heartbreaking to see that he was put into this situation.
"What saddens us further is that Rhodri had ultimate faith in and loyalty towards the organisation and system in which he worked. He had so much more life to live."
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