Farnborough Air Show

CFM Fixes Leap Turbine Shroud Coatings

 - July 17, 2018, 3:42 AM
Turkish carrier Pegasus Airlines was the first operator to put the LEAP engine into commercial service, on an A320neo in the summer of 2016.

As of June, all new-production CFM International Leap-1A and Leap-1B engines delivered to Airbus and Boeing incorporate the permanent ceramic matrix composite (CMC) fix developed by CFM International. The fix mitigates an environmental barrier coating degradation issue that affected the CMC shroud surrounding the first high-pressure turbine stage of in-service examples, according to Gaël Méheust, president and CEO of the CFM joint venture.

Stressing that the CMC environmental barrier coating premature-loss problem has never represented a safety issue for any Leap engine, Méheust told AIN that, nonetheless, it has affected adversely the time on wing many in-service engines have been able to achieve. Loss of the coating reduces the amount of exhaust gas temperature (EGT) margin available to Leap engines, affecting their performance levels at high thrust settings. This lead to operators sending engines prematurely for performance-restoration maintenance shop visits after only a few thousand hours’ time on-wing.

Méheust said the coating degradation problem “is manifested after several thousand hours [in service] and is impacting both [Leap-1A and Leap-1B] models.” However, while by late June operators had sent about 70 engines to CFM and its MRO partners for premature performance-restoration work, all engines removed by that date had been Leap-1As installed on Airbus A320neos, he confirmed. The Leap-1A-powered A320neo entered commercial service in late summer 2016, on an aircraft operated by Turkish carrier Pegasus Airlines. This was at least eight months before the first Leap-1B-powered Boeing 737, a 737 Max 8 operated by Malaysian carrier Malindo Air, entered commercial service on May 22, 2017.

Once CFM became aware of the problem, it acted quickly to provide a temporary fix, according to Méheust. The fix relied on the fact that the designs of the two Leap models “had available extra EGT margin” which CFM knew about from testing but hadn’t yet made available to operators. So CFM engineers “were able to restore 25 degrees of EGT margin through a service bulletin,” which instructed Leap operators to implement a Fadec software upgrade that immediately provided them with some additional time-on-wing flexibility.

“This is very important, because it gives us the time to organize the return of engines to the shop” and deliver spare engines to operators before any operator needs to ground any aircraft as a result of having to remove prematurely a Leap which doesn’t have enough EGT margin available to continue operating, said Méheust. The additional time-on-wing flexibility has allowed CFM and operators to organize Leap removals and replacements without any aircraft on ground emergencies occurring.

“We don’t want any and we haven’t had any,” said Méheust. “We have special teams that do nothing but deal with the airlines and monitor their engine performance.” In addition, “we are doing quick [MRO] turn times to get these engines back” into service rapidly.

With the temporary fix in place, CFM developed a permanent fix for the coating-degradation problem by changing the bonding material it had used to bond the environmental barrier coating to the surface of the CMC shroud segments. (The coating is required because the silicon carbide fiber/silicon carbide matrix CMC parts are adversely affected by water vapor in the exhaust gas flowing from the combustor.) “The fix was introduced in June into the production lines,” said Méheust.

Having the permanent fix in place is particularly important “because we see more and more that airlines are using [Leap-powered] A321neos and 737 Maxs on longer legs, exceeding eight hours,” he said. As a result, the Leap engines on these aircraft are rapidly accumulating substantial amounts of flight hours and providing CFM with lots of operational performance data. “We are very positive that Leap has the best-in-class performance … [and] the longer the leg, the better the fuel-burn improvement,” he said.