Lockheed Martin's F-35 fighter jet grounded

WASHINGTON Oct 1 (Reuters) - Flight testing of all three models of the F-35 fighter jet, the Pentagon's costliest arms purchase, has been suspended pending tweaks to the fuel system software, Lockheed Martin Corp (LMT.N), the plane's manufacturer, said on Friday.

The grounding's impact on the flight test schedule is unknown, John Kent, a company spokesman, said in an email after the close of markets. (Editing by Carol Bishopric)