Procedural shortcomings around the removal and storage of protective engine intake covers aboard the Royal Navy (RN) aircraft carrier HMS Queen Elizabeth led to the UK’s loss of a Lockheed Martin F-35B on take-off, a formal investigation has concluded.

F-35B launch from HMS Queen Elizabeth

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The F-35B uses a ski-jump ramp to take off from Royal Navy aircraft carriers

The incident, which happened in the Mediterranean Sea off the north coast of Egypt on 17 November 2021, resulted in the aircraft, BK-18 (service registration ZM152), being written off at an estimated cost of £81.8 million ($104 million).

The UK’s Defence Safety Authority published its service inquiry findings on 10 August, although multiple key sections detailing the actual accident sequence were redacted due to security considerations.

However, leaked video footage which appeared online shortly after the mishap showed the short take-off and vertical landing aircraft, assigned to the Royal Air Force’s 617 Sqn, fail to accelerate correctly before clearing the vessel’s ski-jump ramp and falling into the sea.


Having ejected following an unsuccessful attempt to abort the departure, its pilot came down on the launch vessel “six feet to the right of the take-off ramp, [and] three feet back from the front edge of the deck”, the report states. With the parachute canopy “snagged on the ramp end light shroud and the flight deck nets”, and his personal survival pack “hanging over the front of the ship”, the pilot quickly unstrapped from the harness.

As emergency personnel responded, the aircraft was seen passing by the side of the ship “floating on the surface, semi-submerged up to the canopy, but with the wings, tail, lift fan and auxiliary doors above water level”.

“Several witnesses saw a ‘large red object’ pushed up and out of the auxiliary intake on top of the aircraft,” the report says. This was subsequently recovered and identified as “BK-18’s left [engine] intake blank”; a removable foam-filled cover.

UK F-35B sinking with intake cover visible

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Engine intake cover floated clear of sinking aircraft as it passed by side of HMS Queen Elizabeth

“The panel concluded that it was almost certain that wind dislodged the left intake blank in BK-18 from its installed position and moved it to a point at which it could not be seen externally on the night of 16 November,” the report says.

Once dislodged, the cover is believed to have moved to “the front face of the engine compressor”, where it remained for the aircraft launch. The investigation team notes that “items located in the intake duct could only be discovered by someone climbing into the intake to look, not just observing from the ground”.

F-35B with dislodged engine intake blank

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Investigators replicated dislodged engine intake blank position after 2021 mishap

During a pre-flight walkaround inspection, which included checking inside the intakes, “the pilot reported not seeing the intake blank”, the report says. However, “BK-18’s pilot noticed the undercarriage pins were still installed, removed them and handed them to the see-off team.”

The panel’s investigation found that an engineering team had worked on the aircraft the night before the incident, and failed to remove all of its protective equipment, referred to as ‘Red Gear’.

“Eng [engineer] 1 observed the Red Gear fitted to BK-18. A full set of Red Gear was too bulky to be carried by one person, so on completing their servicing they took the right intake and Power Thermal Management System blanks down to the hangar. They left the exhaust and left intake blanks in place and assumed Eng 2 would collect them. However, no formal handover was conducted and they did not discuss the partial removal of Red Gear.”

It notes than when another aircraft took off from the carrier earlier on the incident day, “an exhaust blank was dislodged from a UK aircraft on [parking spot] ‘knuckle alpha’. It rolled aft to the Fly 1 section, entered the catwalk, away from the runway, and was recovered by aircraft handlers.”

This prompted an inspection, after which “all visible 617 Sqn blanks were recovered and stowed”, but “at around 07:45 it was reported to FLYCO [the ship’s flying control tower] that another exhaust blank [from BK-20] was seen to fall past the aft reception point and was lost into the sea.” The aircraft had been parked with its tail overhanging the edge of the vessel’s forward lift.

Investigators found that a total of “six related blank issues occurred on the night of 16 November and morning of 17 November”.


Noting that “The [removed] blanks were not stored in set order, so it would have been difficult to identify incomplete sets”, the report states: “In the panel’s opinion, at all levels of the [UK F-35] Lightning programme, Red Gear was not perceived as a threat. This perception caused it to be treated less rigorously than other tools and instruments. The perception [was] that Red Gear was only a risk to other aircraft or personnel, not a threat to airworthiness of the aircraft.”

F-35B in hanger at RAF Marham

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File image shows F-35B with its protective ‘Red Gear’ fitted

Meanwhile, investigators also highlighted the standard launch procedure chosen for F-35Bs aboard Queen Elizabeth – which involved using “a position as far forward on the deck as possible, usually 350ft” – was an aggravating factor. This meant that from the pilot commencing an attempted abort to the aircraft reaching the top of the ramp took just 3s.

“The accident was reproduced in the simulator with the aircraft starting at the 500ft point. It was determined that in this scenario, had the abort decision been made after the same elapsed time, it was possible to abort successfully.”


The panel also notes that UK F-35B pilots had been taught that once brakes have been released for take-off “there was no abort option available to them. They were expected to continue a take-off regardless of aircraft failures, and manage any problem when airborne, or eject.”

Notably, the mishap occurred during the latter stages of the UK’s Carrier Strike Group 21 deployment – its first major operational test of the F-35B aboard the RN’s 65,000t flagship.

UK F-35B BK-18 on sea bed

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Aircraft BK-18 was located and recovered from sea bed depth of around 2,000m

BK-18 was subsequently “discovered intact, inverted on the seabed, at a depth of 2,000m, with a few minor parts such as the ejection seat detached but close to the airframe”. It was recovered via a salvage operation and returned to the UK at a cost of £2.6 million. Cirium fleets data records it as having entered service with the UK customer on 25 July 2019.

Additionally highlighting two recorded F-35 “undercarriage pins-related” incidents which “could have had a serious outcome”, the panel cautions that this indicates a trend of “failure to follow process” by the Lightning Force.

“The Lightning Force will be subject to additional assurance activity as part of a programmed Director Force Generation audit in Autumn 2023,” it notes.