An in-flight fire that erupted on a Marine F-35B last year was caused by a flawed bracket that the Pentagon’s F-35 Joint Strike Fighter program office should have known was a serious hazard, according to a Marine Corps investigation.

The weapons bay bracket that caused the fire was a “known and previously identified hazard in the F-35B community,” the commander of Marine Aircraft Group 31 wrote in an endorsement of the investigation.

“The Joint Strike Fighter Program Office (JSFPO) should have assessed the risk of the broken bracket as more severe than Marginal, properly assessed the root cause of the broken brackets, and implemented a long-term solution to prevent bracket failures,” according to a redacted copy of the investigation, which Marine Corps Times obtained through a Freedom of Information Act request.

On Oct. 27, 2016, a fire broke out while the F-35B was in the air. The plane’s warning system identified the malfunction, allowing the pilot to land safely at Marine Corps Air Station Beaufort, South Carolina, a 2nd Marine Aircraft Wing spokesman said.

The broken bracket had chafed against electrical wiring, which is near hydraulic lines, the investigation found. An electrical short ignited fluid from a pinhole-sized leak in the hydraulic line.

“The Joint Strike Fighter Program Office should re-evaluate the risk severity of the faulty bracket design in order to prevent re-occurrence of an in-flight fire or the potential loss of an aircraft,” wrote the commander, whose name was redacted.

The investigation is the latest criticism for the F-35 program, which is the most expensive weapons program in U.S. military history. A spokesperson for the F-35 program was unable to provide a comment for this story on Friday afternoon.

The Marine Corps’ investigation also criticized the aircraft’s pilot warning system, which can “be confusing and task saturating for pilots” during complex emergencies because there is no way of knowing which warning is the most serious, the investigation found.

In this case, so many warning lights flashed in such a short period of time that it would be difficult for an experienced F-35 pilot to prioritize them, the investigation found.

The pilot did handle the situation in “a safe, efficient and professional manner,” and should not be held responsible for any damage to the aircraft.