Japanese production of the F-35A stealth fighter remains stuck on the tarmac, a recent survey by Japan’s Board of Audit shows.

The Air Self-Defense Force plans to adopt the cutting-edge fighter jet, but nothing is happening due to several delays in the process, leading the audit board to conclude that the effects of Japanese corporate participation in F-35A production in maintaining and strengthening the country’s defense production and technology base have yet to be fully seen, according to the survey, released Wednesday.

The F-35 stealth fighter was developed jointly by nine countries, including the United States and Britain, while Lockheed Martin of the U.S. is in charge of designing and production. The Defense Ministry decided to procure the F-35 under the U.S. government’s Foreign Military Sales program on condition that Japanese companies are allowed to join in production and repairs.

Mitsubishi Heavy Industries Ltd. was picked for final assembly and checkups, IHI Corp. for engine parts production and Mitsubishi Electric Corp. for radar parts production. The three were set to conclude subcontracts with foreign firms partnered with the U.S. government.

In the initial plan, the three companies were supposed to join production of F-35s to be delivered to Japan in fiscal 2017 under the fiscal 2013 contract.

MHI moved ahead based on the schedule, but IHI and Mitsubishi Electric had not signed parts production subcontracts as of the end of fiscal 2016.

IHI fell behind due to a delay in the supply of materials from Pratt & Whitney of the U.S., an original contractor. In addition, after the U.S. government raised information security requirements, IHI took time overhauling its production system.

Mitsubishi Electric failed to meet the schedule partly because of a delay in Lockheed’s orders to Northrop Grumman, another original contractor.

Two F-35s contracted in fiscal 2013 do not have parts from IHI and Mitsubishi Electric. Their parts also may not be used for four F-35 aircraft contracted in fiscal 2014 for delivery in fiscal 2018, sources said.

The board of audit said that checks by the Defense Ministry’s Acquisition, Technology and Logistics Agency on the Japanese subcontractors’ manufacturing processes are insufficient, urging the agency to coordinate with the U.S. government to ensure that items required for F-35 production under the FMS program will be supplied quickly.

An official of the ministry said, “We sincerely take the board’s advice and will continue efforts to ensure appropriate procurement.”