A jet on the bottom of the Mediterranean shows why even small parts can cause big problems for the F-35

• A British F-35B crashed during takeoff from the aircraft carrier HMS Queen Elizabeth in late 2021.
• An investigation found the accident was caused by an air intake cover that was lodged in the intake.

Why a US Marine Corps F-35B crashed in South Carolina this week is yet to be determined, but as the crash of a British F-35B two years ago showed, even a simple maintenance error can bring down a $100 million jet.

In August, Britain's Ministry of Defence released the final report on the loss of a Royal Navy F-35B that crashed into the Mediterranean Sea in November 2021 while taking off from the aircraft carrier HMS Queen Elizabeth, which was on its maiden deployment.

The pilot managed to eject safely and parachute onto the flight deck, but the aircraft sank to the seafloor, where it was found mostly intact in 6,500 feet of water and was eventually recovered.

Investigators determined the accident was caused by an air-intake cover that became lodged in the intake before takeoff. The F-35B, which is the short-takeoff-and-vertical-landing variant of the stealth jet, needed 38,000 pounds of thrust to launch from Queen Elizabeth's ski-jump flight deck, but the blocked intake meant the single-engine jet could only generate 31,500 pounds of thrust.

Wisely, the pilot ejected rather than try to continue a takeoff that probably would have failed to get the plane safely airborne.

High winds apparently blew the cover — known as a "blank" and one of several pieces of "Red Gear" meant to protect the jet's surfaces — into the intake. This wasn't detected because the design of the F-35B's inlet duct creates a blind spot where foreign objects in the duct can only be spotted by someone climbing into the intake.

Royal Navy crews were not aware of this problem as they learned to handle a new aircraft. "Lack of familiarity with this design feature and the associated potential for items to be concealed in the intake was a contributory factor," the investigators concluded.

The problem was exacerbated by a lack of record-keeping and documentation. According to the investigation, it wasn't evident to the crews that not all the engine covers had been removed from the aircraft and returned to storage.

In addition, personnel shortages led to ground crews being overworked and to insufficiently trained maintainers being hastily transferred from the Royal Air Force to the Queen Elizabeth. (Britain's F-35Bs are jointly operated by its air force and navy.)

But the accident report also raises issues that should concern the more than 20 nations that operate or plan to acquire F-35s. Engine covers — which are used to shield the jet's sensitive components from debris as well as from the prying eyes of enemy spies — have repeatedly been lost or fallen from the aircraft during towing, British investigators say.

"The panel determined that these issues occurred across the global F-35 user community but were at a level such that it was considered a 'nuisance,' rather than a documented failing," the report said. "This resulted in learned behavior of the poor performance of the Red Gear being a feature of F-35B operations."

Since the F-35, which has three variants, entered service in 2015, about a dozen have crashed, with the accident rate being on a par with other military aircraft. But interestingly, the British report listed multiple F-35 incidents — mostly with US aircraft — involving covers and plugs in the intake.

These include a 2014 mishap with a US Air Force F-35A that suffered an engine stall in flight, a plug left in the intake of a Marine Corps F-35B during a ground test in 2015, and a 2020 incident where a US Navy F-35C had to abort takeoff because of a cover stuck in the intake. In addition, British F-35s experienced engine blanks being blown across the runway or even wrapped around a lower lift fan door.

At this point, there's no reason to believe that engine covers had anything to with the recent crash in South Carolina, but, as shown by that jet on the bottom of the ocean, even a small error with a minor piece of equipment can have catastrophic consequences for an aircraft as complex as the F-35.

Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds a master's in political science. Follow him on Twitter and LinkedIn.