EAST HARTFORD, Conn., May 21 (UPI) -- Connecticut-based Pratt & Whitney received an up-and-away flight operations certification for its F135-PW-600 short-takeoff/vertical-landing propulsion system.

The certification, from the U.S. Defense Department's F-35 Lightning II Joint Program Office, is a statement of qualification for Pratt & Whitney's F135 STOVL system, critical in the development of the F-35 Lightning II STOVL striker aircraft variant.

Company officials are calling the certification a milestone after more than 9,800 test hours conducted on the system. The announced certification adds to the F135 STOVL system's endurance and durability qualification, awarded after sea level and accelerated mission testing.

"This certification letter is a step on the critical path to flying the aircraft and brings us closer to powering the first flight of the F-35 Lightning II STOVL variant this spring," Bill Gostic, Pratt & Whitney vice president, F135 engine programs, said in a statement.