Engine shutdown error led to fatal Royal Navy Merlin ditching, investigators find

A UK military air accident investigation has concluded that a Royal Navy Leonardo AW101 Merlin HC4 was lost in September 2024 after its crew mistakenly shut down two of the helicopter’s three engines while responding to an engine fault during night deck-landing training.

Lieutenant Rhodri Leyshon, flying from the right-hand seat, died when the aircraft struck the sea at a high rate of descent and inverted roughly 11 minutes after departing the carrier HMS Queen Elizabeth. His body was recovered 115 minutes after impact. The two other crew members escaped safely.

According to the Defence Safety Authority panel’s redacted report, the sortie — the second of the evening, conducted with night-vision goggles — was 0.25nm from the carrier at 65kt and 125ft when the number two RTM322 engine, built by Safran Helicopter Engines, suffered a failure. A rubber diaphragm in the high-pressure fuel metering unit had split, causing a sudden fuel-flow increase and a rapid rise in engine torque and rotor speed, a failure mode known as an engine runaway up.

The investigation found the diaphragm, designed for a 10-year service life, had been installed for three years and nine months. Post-accident analysis indicated the component could be weakened during manufacturer-mandated post-assembly testing. Notably, a second Merlin, ZJ998, had experienced a similar diaphragm failure on its port engine roughly a year earlier while on the ground at RNAS Yeovilton; that engine shut down automatically within three seconds, and analysis of the failure mode was still under way when the fatal accident occurred.

On the accident aircraft, ZJ135, the engine management system reduced output from the remaining two engines to keep torque and rotor speed within limits, and multiple warnings — including a red ENG FAIL alarm and a voice alert — were displayed. The crew overshot the deck and entered the port circuit to attempt a rolling landing, but the subsequent actions led to both remaining engines being shut down, condemning the helicopter to ditch. The report is heavily redacted and the released text cuts off before the full sequence of those actions.

The Merlin programme sits within Leonardo’s helicopter business; Leonardo DRS (DRS), the US-listed defence electronics affiliate, trades separately and was recently quoted at $36.06, down 3.19% on the day.

What to watch

• Any follow-up actions from the Defence Safety Authority, including the full unredacted findings and recommendations on engine procedures and training.
• Safran Helicopter Engines’ response regarding diaphragm manufacturing and post-assembly test processes, and whether fleet-wide inspections or component changes are ordered across the Merlin fleet.
• Any updated fleet restrictions or resumption timelines for night deck-landing training sorties from Royal Navy carriers.

Source: original release