First flight of the U.S. Navy's Northrop Grumman X-47B unmanned combat air system demonstrator has slipped into the first quarter of 2010 after propulsion acoustic and engine-start sequencing issues uncovered during ground checkout at Edwards Air Force Base, Calif., forced adjustment and additional testing.

Low-speed taxi tests are now expected to begin no later than December, a Navy statement announced this afternoon, adding that sea trials of the carrier-capable UCAS-D remain on schedule for 2012. More information could not be immediately obtained from the Navy.

Northrop declined an AVIATION WEEK request for comment. A company representative said tonight that a "moratorium" had been placed on providing press interviews for UCAS.

The test flight was once eyed for this month, officers said in May at the Navy League's Sea-Air-Space show near Washington. Officials and executives even enjoyed public banter over the summer about flying the demonstrator in whole or in part en route to Patuxent River, Md. But by August, officials already were acknowledging they pushed the first flight out several weeks so they could further examine anomalies that arose during proof-load testing.

Photo credit: Guy Norris