Farnborough -- Pratt & Whitney says it is testing and verifying a “more robust” oil system for the PW1500G as part of company-wide efforts to return the grounded Bombardier CSeries test fleet to the air as soon as possible.

Speaking in detail for the first time about the May 29 uncontained failure which halted the CSeries flight test program, Pratt says the chain of events has been traced to leaking oil seals. The issue led to reduced lubrication around bearings in the low pressure turbine, eventually triggering a failure during ground runs on engine number one on CS100 test aircraft FTV-1.

Describing the event as a “minor speed bump on the overall development path,” Pratt & Whitney PW1000G vice president and chief engineer Graham Webb says “there was an issue with the oil system that we are making modifications for.” The problem, he adds, was a “plumbing issue” and extensive testing is taking place across several Pratt facilities in North America to “ensure validation of the fix is robust.”  Webb declined to provide more specific details of the modifications but says unexplained high rates of oil consumption that preceded the failure had assisted in pinpointing the cause.

The company says “one or two” minor parts of the engine will be changed, but adds “we don’t have any plans to change parts of the low pressure turbine.” The fan drive gear system at the heart of the PW1000G family, which is lubricated and cooled by a dedicated oil system, was not a factor in the event and has continued to operate as planned throughout the test program says Pratt.

No timeline for completing the tests has been given.  “We have gotten a certain part of the way through it. You don’t know for certain you are done until you’re done,” says Webb.