Pratt & Whitney has made a preliminary determination of the root cause of the PW1500G geared-turbofan engine failure during ground tests on a CSeries and is working with Bombardier "on a plan to resume testing in the next few weeks," says Greg Hayes, CFO of parent company United Technologies.

"We believe we have an understanding of what has occurred," he told analysts this morning. "If we are correct in our thinking it can be rapidly fixed."

The uncontained failure occurred on May 29 at Mirabel, near Montreal, during stationary ground maintenance testing of the first flight-test CSeries, aircraft FTV-1. The incident damaged both the engine and the aircraft.

Bombardier stopped all flying, but has continued ground testing on aircraft FTV-2, -3 and -4. The engine was shipped to Pratt’s Connecticut plan for tear-down and inspection.

While the investigation continues, Hayes said "We believe we have come to a preliminary root-cause analysis, and it will not have a significant impact on the testing schedule."

Hayes did not detail the suspected cause, but said "it does not relate to anything to do with the fan drive gearbox. It is something much simpler than that." Some unconfirmed reports have tied the incident to the engine’s oil system.

Bombardier, meanwhile, says the aircraft is "very repairable." FTV-1 is the envelope-expansion, handling-qualities and engine test aircraft, but FTV-2 is fully instrumented as a backup.

The manufacturer says it still plans to begin deliveries of the initial 110-seat CS100 variant in the second half of 2015, already a slip of more than 18 months from the original schedule.