F-35s are available to fly just 55% of the time and 73% of replacement parts have to be sent back to suppliers because the Pentagon’s maintenance depots are inadequate, according to a new congressional audit on the troubled upkeep of the fighter jet that is the world’s costliest weapons system.

The report released Thursday by the Government Accountability Office came days after a $100 million F-35B crashed over South Carolina. The warplane’s Marine Corps pilot, who had been on a training mission, ejected safely.

The Marine Corps has only begun its investigation into what went wrong. But the GAO report updates the persistent maintenance shortcomings of the advanced fighter fleet built by Lockheed Martin, which is expected to cost a total of $1.7 trillion including decades of operations and maintenance.