LONDON—An investigation into the loss of a British F-35 Joint Strike Fighter during carrier operations in the Mediterranean Sea in November 2021 has raised questions about equipment, resource management and program security issues affecting personnel.

The long-awaited 148-page report into the loss of the F-35B ZM152 concludes that it was caused after one of the air intake blanks designed to protect the engine from foreign objects became stuck in the F-35’s intake and reduced engine power as the aircraft made its takeoff roll. The inquiry panel flags contributing factors that may have led to the accident and raises broader concerns with the UK’s approach to embarked operations, making no fewer than 46 recommendations.

Commanders should better understand “safety and security requirements for a fifth-generation platform,” the report says, noting that the “introduction of special access programs” such as the F-35 has “elevated security thresholds, which places extra strain on safety.”

The air intake blank formed part of a set of protective equipment called “red gear,” which was fitted to the sensitive parts of the aircraft when not flying.

This equipment would generally be fitted to the aircraft when the ship was in port “to protect aspects of the aircraft from espionage,” but was not generally used when the ship was at sea because the intake blanks could be blown out by modest winds or aircraft launching nearby.

The report also questions whether 617 Sqdn., the UK’s frontline F-35 unit, was fully ready for the deployment, noting that it “faced a higher operating tempo than it was prepared for, as the Carrier Strike Group aspired to a baseline flying rate associated with so-called surge operations.”

Personnel had not received the necessary levels of training for operations at sea, the report finds, noting there were high levels of fatigue.

Rates of flying, it says, resulted in decreased opportunities for fresh air and recreation for those personnel without routine access to outside spaces, contributing to fatigue. The report noted that some witnesses described the Queen Elizabeth carrier as “the largest submarine in the Navy.”

These issues contributed to the accident, the investigation panel found.

The probe found that the presence of the intake blank caused a minimum 17% deficit between demanded and delivered thrust during the takeoff roll. While the pilot requested 38,000 lb. of power through the throttles, only 31,500 lb. was delivered, the report said.

The pilot elected to abort the takeoff as the aircraft reached the carrier’s ski jump. He reduced the aircraft’s throttle to idle and applied the brakes. As the aircraft went over the ramp, the pilot initiated the ejection sequence.

The report says that a combination of the wind, the forward movement of the ship and the swing of the parachute meant that the pilot landed on the deck, 6 ft. to the right of the takeoff ramp and 3 ft. back from the front edge of the deck, while the parachute canopy snagged on the ramp end light shroud and the flight deck nets at the right-hand side of the top of the ramp.

The aircraft floated alongside the ship for a short time before sinking. It was later discovered intact upside down on the seabed at a depth of 2,000 m (6,562 ft.). As the aircraft flooded, the air intake blank which caused the incident was seen floating out of the air intake.

The report notes there had been several reports of the air intake blanks being dislodged, blown out or being lost overboard from the ship. It says there had been four similar incidents involving air intake blanks on U.S. aircraft, but they did not result in aircraft loss.

ZM152 was later recovered from the seabed at a cost of £2.63 million ($3.35 million).

In his closing remarks, Air Marshal Steve Shell, director general of the UK Defense Safety Authority, says the UK’s Lightning Force—the joint Royal Navy-Royal Air Force organization operating the F-35—had not yet reached a “critical mass,” with squadrons unable to support each other’s deployments without infringing on their own operations. “Until critical mass is reached, defense must recognize the trade-offs between readiness, growth and safety,” he says.

He added that with UK F-35 operations increasing and the government wanting to expand carrier deployments, the accident had been a “timely reminder to take stock and ensure we are giving the Lightning Force the best chance of success.”