The second Bombardier CSeries CS100 flight-test vehicle returned to the air on September 7 after more than a three-month hiatus. FTV2 took off at 6:10 p.m. from Bombardier’s facilities in Mirabel, Quebec, for a 30-minute “return-to-service maintenance flight,” during which flight test pilots Muz Colquhoun and Chuck Ellis took the airplane to an altitude of roughly 10,000 feet and a top speed of 245 knots. The flight marked the successful resolution of an engine lubrication “issue” that resulted in an uncontained failure of the first flight-test vehicle’s left Pratt & Whitney PW1524G on May 29.

“Following the pause of the CSeries aircraft flight-test program...Pratt & Whitney and Bombardier finalized a solution that Pratt has since incorporated into the engine’s oil lubrication system,” said CSeries program vice president Rob Dewar. “In spite of the flight-test program pause, we are still confident that entry-into-service will take place in the second half of 2015.”

The uncontained failure of the left engine on the first flight-test vehicle damaged the airplane’s left carbon-fiber wing. Experts from Bombardier’s Short Brothers composites plant in Belfast have nearly finished their repairs, said Dewar.

Bombardier stressed that engineering teams used “downtime” during the pause in flight testing to complete more ground tests, configuration and software upgrades, training for entry into service, telemetry and system analysis based on data collected so far “and a number of other activities that would have been required per the schedule.”

Since launching the program in 2008, Bombardier has announced no fewer than four separate delays to the CSeries, the most recent of which shifted expected certification from September 2014 to the second half of 2015, giving the company a six-month window in which to accomplish its goal. Originally expected to gain certification by the end of last year, the CSeries experienced several delays to first flight before finally taking to the air last September.

Between then and the time of the engine failure four flight-test airplanes had flown some 330 hours during about 100 sorties. On June 10 Bombardier confirmed it had restarted ground testing, and said it and Pratt & Whitney had gained a “very good understanding” of the sequence of events that led to the incident. On Friday Dewar reported that the now certified modifications did not affect the engines’ thrust, emissions or noise performance.

During July’s Farnborough airshow, Pratt & Whitney identified the source of the failure as a “seal issue” in the oil system, not the low-pressure turbine as previously indicated by Bombardier. Still, Pratt & Whitney executives resisted any temptation to precisely identify what engineers believe caused the uncontained failure. “The area that was affected was in the back end of the engine, but that’s all we are saying,” said Pratt & Whitney Commercial Engines president David Brantner. “I don’t want to speculate about anything else…the issue is a seal problem in the oil system.”