The weight of the new plane remained fairly steady over the past year, and the mean time between critical failures increased, but the plane’s performance remained below the level expected for this point in the program, the report said.

The report also cited continuing delays with Lockheed’s delivery of software for the new fighter, noting that software packages needed to support flight test were delayed or not complete when delivered.

It said the complex helmet that integrates data for the pilot from all the plane’s sensors was still facing issues, as is a computerized logistics system.

Weapons integration testing was delayed by a number of factors, including problems with the performance of a radar system and in tracking targets.

Durability testing of the Marine’s B-model had to be halted in December after multiple cracks were found on the underside of the plane’s fuselage, the report said.

It also cited problems with the ability of the Navy’s C-model to transfer video and imagery data to ships, and said one live-fire test revealed a potentially serious problem with the coolant system, which was now being addressed.

More work was also needed on a system aimed at protecting the plane from fuel tank explosions caused by lightning, the report concluded, noting that flight operations were currently banned within 25 miles of known lightning conditions.

No immediate comment was available from the Pentagon’s F-35 program office.