A British military inquiry found that a split engine diaphragm set off a cascade of mechanical and crew errors that left a Royal Navy helicopter powerless over the English Channel, and Lt Rhodri Leyshon trapped inside as it sank.
Leyshon, a pilot seated in the right-hand seat of a Merlin Mk4 helicopter, died on 4 September 2024 after the aircraft ditched into the sea roughly 25 nautical miles south of Lyme Regis, on the Dorset coast. The night-flying training exercise turned fatal in minutes. A service inquiry conducted by the Defence Safety Authority has now released its findings, identifying both an engine component failure and a critical crew misreading of cockpit instruments as factors in the crash, the BBC reported.
Three crew members were aboard the Merlin Mk4, which was operating out of Royal Naval Air Station Yeovilton in Somerset. The other two survived with minor injuries. Leyshon was not recovered from the water for approximately two hours. He was pronounced dead at a hospital whose name has not been disclosed.
A split diaphragm started the chain reaction
The inquiry traced the disaster's origin to a diaphragm inside one of the helicopter's engines. The component split during flight, and the consequences compounded fast. The service inquiry report stated plainly what happened next:
"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."
That overspeed condition on one engine created confusing readings in the cockpit. The crew members, flying in darkness over open water, misread the situation. They concluded, wrongly, that two of the helicopter's three engines had failed.
The inquiry report found that the crew "erroneously concluded that the number one and three engines had failed." Acting on that mistaken assessment, they manually shut down both engines. That left the aircraft running on only the one engine already malfunctioning from the fuel overflow.
It did not last. The remaining engine hit what the inquiry called its "overspeed trip threshold" and automatically deactivated. All three engines were now offline. The helicopter had no power.
Military helicopter crashes remain an unsettling recurring theme across Western armed forces. In the United States, two Fort Hood soldiers were killed in an Apache crash near Salado, Texas, in another incident that raised questions about aircraft maintenance and training safety.
Lt Leyshon could not escape the sinking aircraft
With no engine power, the Merlin Mk4 descended into the English Channel. The inquiry described the landing as a deliberate emergency ditching, a controlled crash onto water, but the impact was severe enough to cause serious injury.
The report found that Leyshon had been "seriously injured" during the impact and was "unable to escape from the aircraft as it entered the water." The two other crew members managed to get out and sustained only minor injuries. Leyshon remained trapped.
Rescue teams did not reach him for roughly two hours. By the time he was pulled from the water, it was too late. He was taken to a hospital and pronounced dead. The inquiry has not disclosed whether the delay was caused by the remote location, 25 nautical miles offshore in darkness, or by other factors.
The incident carries echoes of other naval aviation disasters in recent months, including a U.S. Navy Sea Hawk helicopter that went down in the Arabian Sea with a crew member still missing.
Helicopter destroyed, recovered in two pieces weeks later
The Merlin Mk4 sank to the seabed and was damaged beyond repair. Recovery crews pulled the wreckage up in two major sections, the first on 12 September 2024, the second on 23 September. The salvage operation took nearly three weeks from the date of the crash.
The recovered wreckage presumably formed the physical basis for the inquiry's mechanical findings, though the report does not describe the forensic process in detail. The split diaphragm was identified as a key failure point, but the inquiry has not publicly stated which of the three engines contained the faulty component or what caused the diaphragm to fail in the first place.
Naval vessels and aircraft operating far from shore face unique dangers when systems fail. The USS Benfold lost all power in the South China Sea earlier, stranding 300 sailors for four days, a reminder that mechanical breakdowns at sea can leave service members with no margin for error.
Forty-four recommendations, but few details made public
The service inquiry panel issued 44 recommendations in the wake of Leyshon's death. Air Marshal Alan Gillespie, the Director General of the Defence Safety Authority, urged all commands to consider them. But the specific content of those 44 recommendations has not been made public in the reporting so far.
That gap matters. Forty-four recommendations suggest the panel found problems well beyond a single faulty diaphragm. Were the findings about cockpit instrument design? Crew training for engine-failure scenarios at night? Emergency egress procedures? Rescue response times? The number alone signals systemic concern, but without the details, the public, and the families of service members who fly these aircraft, cannot evaluate whether the fixes will be real or bureaucratic.
Gillespie offered condolences in a statement released alongside the findings:
"On behalf of the Defence Safety Authority and the wider Defence Aviation community, I offer my sincere condolences to Lt Leyshon's family, friends and colleagues."
Condolences are appropriate. But families of military personnel lost in training accidents, whether in Britain or the United States, where two soldiers died in another helicopter crash near Fort Hood, deserve more than sympathy. They deserve transparency about what went wrong and proof that the same failure will not happen again.
What the inquiry still has not answered
Several critical questions remain unaddressed. The inquiry has not disclosed what caused the diaphragm to split, whether it was a manufacturing defect, wear, improper maintenance, or something else. It has not identified the specific engine involved. The identities and roles of the two surviving crew members have not been released.
Perhaps most importantly, there is no public indication of whether the Royal Navy has grounded or ordered inspections of other Merlin Mk4 helicopters in the fleet. If a diaphragm failure in one engine can produce a chain reaction that drops a helicopter into the sea, the obvious question is whether the same component in other aircraft is at risk.
The Defence Safety Authority has not stated whether the full inquiry report will be published. A link to the authority's official page exists on the UK government website, but the report itself does not appear to have been posted for public review.
Military readiness depends on equipment that works and crews trained to handle it when it does not. Lt Rhodri Leyshon went up for a routine night exercise and never came home. Forty-four recommendations sitting in a file do nothing for the next crew unless someone acts on them, and unless the public can verify that they did.
