Dassault Aviation’s long-delayed Falcon 5X big-cabin business jet development program faces a further holdup after Safran Aircraft Engines revealed it had encountered new problems with the aircraft’s Silvercrest turbofans during recent ground and flight tests.

Engine development issues have already forced Dassault to delay entry-into-service of the Falcon 5X to 2020, and Eric Trappier, the company’s chairman and CEO, says it is still too early to know how long the latest problems will further impact the revised schedule. First announced at NBAA in 2006, the Silvercrest was launched by Dassault to power the Falcon 5X, which was originally targeted at entry-into-service in 2017.

Clearly exasperated with the emergence of this new hurdle, Trappier says “Safran informed us, just before we left for Las Vegas, that ongoing tests have revealed some performance issues with the high-pressure compressor [HPC]. We have not yet analyzed all the consequences, but we already know the 5X entry-into-service, which was rescheduled to 2020, will be delayed again.”

Although Trappier declined to comment specifically on whether the latest test event has finally pushed Dassault to the brink of considering an alternative engine supplier, he says “it is too early to say. We are now trying to fix the problem with Safran, and we are trying to keep all our options open.” Trappier adds: “The consequences of this unfortunate issue and defining an appropriate solution will take some time.”

As if to underline Dassault’s increasing frustration with the engine situation, Trappier insisted in a press conference that detailed questions about the issues be answered directly by Cedric Goubet, vice president of commercial engines at Safran, who was seated in the audience. Although initially clarifying that Safran has “designed, validated and implemented the solutions for most of the technical issues we had faced two years ago,” Goubet acknowledges that “very recent flight testing on the flying testbed [a modified Gulfstream 2] in San Antonio, Texas, has shown the new engine configuration does not completely match our expectations.”

Goubet adds that “the fact is there seems to be a need to further improve the responsiveness of the high-pressure compressor. This is not an issue with the overall performance of the engine. It’s an issue with the efficiency of the compressor in certain operational conditions such as very high altitude or low speed where it is lacking responsiveness. For example, [it does not] deliver adequate acceleration and deceleration as expected by the pilots and the airplane. We understand this pretty well, and now we need to precisely define the solution with our customer and in which timeframe we can incorporate them.”

Silvercrest features a single-piece wide-chord titanium fan and four-stage booster powered by a four-stage low-pressure turbine. However, in an unusual departure from most turbofans in the upper mid-thrust power range, the high-pressure section is comprised of a four-stage axial compressor combined with a single centrifugal compressor powered by a single-stage high-pressure turbine with active clearance control. Other than clearance control challenges, the high-pressure section is not known to have been the source of previous problems for the development program. Up until two years ago, issues were mostly associated with the oil-fuel heat exchanger and carcass distortion.

The engine has also been selected by Textron Aviation for the Citation Hemisphere, and it remains unclear whether the newest delay may impact this program, which is slated for first flight in 2019. In the meantime, Dassault continues flight tests of the Falcon 5X powered by an interim standard of Silvercrest engine. Since making its first flight on July 5, the prototype has amassed around 50 flight hr. and achieved a top speed of Mach 0.8 and a maximum altitude of 41,000 ft. “We are very happy with the way the aircraft handles and also with the performance of the systems. The aircraft has a new generation of digital flight control system, and from what we have seen so far, it works very well,” says Olivier Villa, senior executive vice president of Dassault Falcon Civil Aircraft.