Bombardier has suspended flight tests of the CSeries airliner after a Pratt & Whitney PW1500G on the first development aircraft suffered an unspecified failure during ground runs at the Mirabel, Quebec site on May 29.

According to unconfirmed reports, the failure on FTV-1 caused debris to eject from an engine, while other reports also indicate the presence of smoke. Bombardier, which confirmed “an engine-related incident” occurred during “stationary ground maintenance testing involving the CSeries FTV1,” also says the airframe suffered damage. This supports speculation the event was a high-energy failure such as an uncontained turbine failure.

The manufacturer adds it is “investigating the incident with the support of Pratt & Whitney and the appropriate authorities. Safety is the priority, and the CSeries aircraft flight-test program will resume once the investigation is completed.”

Pratt & Whitney declines to comment directly on either the extent or type of damage suffered by the engine, or whether the event might have implications for the broader development of the PW1000G geared turbofan family. The engine maker says “it’s premature to speculate, as we continue to work with Bombardier to investigate the incident. Transport Canada certified the CSeries engine last February. Pratt & Whitney has an extensive technology risk reduction program and completed more than 9,000 hours of testing across the PurePower engine family, including more than 1,300 hours of flight.”

Pratt says it is also “premature” to speculate about whether the CSeries event is related to the April 29 incident in Mirabel in which an unidentified PW1000G engine on one of the company’s Boeing 747SP flying testbed aircraft suffered “a minor anomaly.” Pratt says “examination of that engine revealed that there was no apparent damage and we were able to run it again the next day. As a matter of policy, and for proprietary reasons, we do not reveal which engine was being tested.” The engine is thought to have been one of the PW1100G versions which is under development for the Airbus A320neo.

Commenting on the April event, Bob Saia, vice president, Pratt & Whitney Commercial Development Programs, says “we do a lot of unique testing on development engines and one of our margin tests had an anomaly.” Saia adds the test was one of several deliberately run toward the end of the test program to verify design and performance margins beyond normal operating parameters. “This particular engine had gone through a long series of tests and the condition of the engine was beyond the end of a certain level of service wear.  We were looking to get a certain data point and we got it.” Pratt Commercial Engines President David Brantner adds the engine showed no damage during a subsequent borescope inspection and was started without incident the following day.

Even if the latest incident is also related to a one-off failure, the engine event adds unwelcome pressure to the already delayed CSeries flight-test effort. After a slow start, the program was in the process of building momentum with the recent introduction of the fourth test airframe, FTV-4, earlier this month. Since the first flight of initial CSeries aircraft, FTV-1, in September 2013, the fleet has amassed more than 100 flights and more than 300 flight-test hours. But with some 2,400 hr. planned, and certification targeted for the second half of 2015, Bombardier is looking to accelerate the test campaign.

FTV-1, which recently completed stall testing, has been flown to the edges of the CSeries flight envelope, reaching Mach 0.82 and an altitude of 41,000 ft. FTV- 2 recently completed extreme temperature testing at the McKinley Climatic Facility in Florida, while FTV-3 remains in Wichita for avionics and electrical testing. FTV-4, which entered the test effort on May 18, is designated as a performance aircraft, while follow-on FTV-5, -6 and -7 are in assembly.