Snecma has revealed more details about the upcoming flight tests of the Silvercrest engine on a Gulfstream II in the U.S. later this year before the evaluation campaign moves to Istres, France, in early 2014.

Although conversion of the Gulfstream in Texas appears to have taken longer than expected, the overall engine development schedule remains on track with certification expected in 2015, says Snecma. The Silvercrest, which will be rated at 11,450 pounds thrust to power Dassault’s newly unveiled Falcon 5X as well as at 11,000 pounds thrust for Cessna’s Citation Longitude, is likely to make its first flight in December, says Snecma Chairman and CEO Pierre Fabre.

“We have had four engines in the test cell as of today,” says Silvercrest Program General Manager Laurence Finet. “There were three engines running together from the beginning of October, and now we have removed the one on an open-air testbed prior to sending it shortly for installation on the flying testbed,” she adds. The unit will be mounted on the right-hand pylon in place of the aircraft’s original Rolls-Royce Spey. “The Gulfstream has been undergoing modification for the past two years in the U.S.” The Gulfstream was selected for the role over other models because of its high altitude capability, the similar thrust size of the Spey and the fact that the aircraft was already owned by Snecma parent company Safran.

“Once we obtain initial flight clearance with the Silvercrest, and conduct some altitude and performance tests, we will take it off and replace it with the original engine. The Gulfstream will fly then to Istres, where the Silvercrest will be refitted and complete the remainder of the flight-test campaign there,” Finet says. The effort, which will be conducted from Snecma’s flight test unit at the French national evaluation site, is expected to last around five months.

In testing, the engine has performed well to date, says Finet. “We have demonstrated and exceeded our full takeoff thrust, and have done performance and operability work. That is not yet complete, but we have good results so far, and we already know we have a sound engine.” Highlights from the early results include snap accelerations in which the engine went from idle to full takeoff thrust in 3.6 seconds. “The acceleration is excellent,” she adds.