Pratt & Whitney, a unit of United Technologies Corp (UTX.N), on Monday said it is working closely with suppliers to prepare for a large ramp-up in production in coming years of the F135 engine that powers the Lockheed Martin Corp (LMT.N) F-35 fighter jet. Bennett Croswell, who heads Pratt’s military engines division, said the company was seeking to ensure it had at least two suppliers for every major component, and was also carrying out production readiness reviews of key suppliers, and the companies that build parts for them.