The Trump administration should “rigorously and comprehensively review” Lockheed Martin’s F-35 fighter jet, the Pentagon’s costliest programme, the US defence department’s director of combat testing said. Michael Gilmore, who will leave the post as testing director when Donald Trump takes office as the US president next week, cited the fighter’s “significant, well-documented deficiencies in critical combat capabilities” in a letter to the House armed services committee chairman Mac Thornberry of Texas, who is a strong supporter of the F-35. While Mr Trump has tweeted that “the F-35 programme and cost is out of control”, Pentagon officials say the plane is now essentially on schedule and close to its budget after earlier problems. But Mr Gilmore focused on unresolved performance issues in the current US$55 billion development phase. These must be resolved before the aircraft can enter intense combat testing and the eventual deployment later this decade of fully capable combat jets. The defence department’s F-35 programme office “has no plan to adequately fix and verify hundreds of these deficiencies using flight testing within its currently planned schedule and resources”, Mr Gilmore wrote. Deploying F-35s “with capable mission systems is critical to our national security” but the programme now “is at high risk of sacrificing essential combat performance”, he added. The Pentagon’s office of independent cost analysis estimates that extending the development phase from its planned test flight completion in September 2017 to as late as into 2020 could cost as much as $1.12bn more. The number is contained in the testing director’s new annual report delivered to Pentagon leaders and policymakers late Monday. The programme office has said completing the phase will require about $530 million extra and acknowledges it may slip to May 2018. Mr Gilmore’s annual report contains a 62-page assessment of the programme that is a detailed primer for the incoming administration on deficiencies that include software, weapons accuracy, aircraft-carrier launching, the diagnostic system and reliability. * Bloomberg business@thenational.ae Follow The National's Business section on <a href="https://twitter.com/Ind_Insights">Twitter</a>