A Marine Corps F-35B caught fire during a late October flight because of a weapons bay defect that military officials knew about and were already working to fix.

Air Force Lt. Gen. Christopher Bogdan, the F-35 program executive officer, told reporters Monday at the program’s offices in Arlington, Virginia, that the Oct. 27 mishap occurred when a bracket that held electrical wires in the weapons bay came loose, allowing the wires to chafe and come into contact with hydraulic lines, causing the fire.

Military.com broke the news about the fire, which caused at least $2 million in damage, according to Naval Safety Center estimates. An F-35B from Marine Fighter Attack Training Squadron 501, a 20-plane fleet replacement squadron for the Marine Corps based in Beaufort, South Carolina, was involved in the mishap.

“The good news is, we knew what it was,” Bogdan said. “When knew about this problem long before that, and all of our airplanes were being retrofitted with a new bracket.”

The F-35B that caught fire had not yet received the replacement bracket, he said, but had been inspected as part of a stopgap regiment designed to prevent mishaps. Prior to the flight, Bogdan said, the bracket had seemed to be holding.

“We inspected, it looked fine, and it just didn’t look fine in the air,” he said.

In the wake of the fire, the Marine Corps opted not to ground any aircraft or pause flight operations. Officials did, however, update the inspection regimen to make assessment of the faulty brackets more rigorous, Bogdan said.

Bogdan acknowledged it was a risk to fly the F-35Bs that had not yet received the bracket retrofit, but said it was one of many risks that come with operating the aircraft.

“Military airplanes all have risk,” he said. “This plane is like no other and yes, there are acknowledged risks, and that would be one of them. Until we fix that bracket, every airplane of the B-model that doesn’t have that bracket is going to have to be inspected, and hopefully that bracket remains in place when it’s flying.”

It’s not yet clear when the retrofit process will be complete or how many aircraft still need the new equipment.