The Pentagon’s operational testing director has stated that the test fleet needs an 80 percent availability rate to meet the demanding schedule of the program’s test and evaluation master plan.

Aircraft mission capability statuses can be degraded for reasons including a lack of spare parts or a failure in a mission system like the radar or electronic warfare instruments. According to sources within the F-35 program, a frequently failing component is the Distributed Aperture System. This system provides the pilot warnings of incoming missiles and generates the imagery for the $400,000 helmet that the pilot wears. The F-35 can still fly with problems like this, and, using the data links between aircraft, some of the information from a functioning system on another F-35 can fill in a blind spot in a degraded one. But this only works up to a point, and to fully test the program’s capabilities, all systems must function properly.

Pentagon officials declined to comment on this report.

The operational test fleet’s low readiness rates are surprising, considering the high-profile nature of the fleet’s mission. Under federal law, a major defense acquisition program cannot legally proceed to full-rate production until the director of operational test and evaluation (DOT&E) submits a final report to the secretary of defense and Congress following the conclusion of the testing process. Because of this, the operational testing fleet receives extra support in the form of larger maintenance crews, and is presumably higher on the priority list to receive spare parts.

The operational test fleet readiness chart shows that aircraft being used for operational testing are actually performing worse than the rest of the F-35 fleet, which could achieve only a 27 percent fully mission capable rate, according to the latest available figures.