Rolls-Royce is fast-tracking the removal of certain older Trent 1000 intermediate pressure turbine (IPT) blades and modifying its blade-life calculation methods in the aftermath of a Norwegian Air 787 engine failure near Rome linked to blades that cracked before established life limits.
The Aug. 10 incident occurred just after Norwegian 787-8 LN-LND departed Rome–Fiumicino International Airport (FCO) for Los Angeles. The left-side engine failure sent blade fragments into the streets of the Rome suburb of Fiumicino. The flight crew shut the engine down and safely returned to FCO.
An update from Italy’s ANSV accident investigation body issued Sept. 4 said that two adjacent IPT blades failed inside the Trent 1000-G/01A—a “Package B” version. The forward blade suffered a “progressive failure,” while the trailing blade suffered an “overload failure,” ANSV said.
The progressive failure is similar to 10 previous Trent 1000 incidents linked to sulphidation-related fatigue caused by pollutants interacting with high engine temperatures. The issue affects both Package B and Package C variants.
Rolls introduced a modified blade last year, and worked with the European Aviation Safety Agency (EASA) to establish life limits for pre-modification blades as the new parts are rolled out. Rolls used fleet sampling and other data to project each blade serial number's exposure to a variety of conditions—including time operated within certain temperature bands and exposure to specific pollutants in different environments—and set life limits. The limits were put in place after the eighth progressive-failure incident, which took place in July 2018.
Investigators determined the progressive failure occurred at 1,210 cycles, or 200 cycles before the blade's projected life limit. The overload failure happened after 1,337 cycles—103 cycles before the blade's life limit.
The premature failures suggest that Rolls’ hard-life limits are “not sufficient to avoid detrimental effects on safety,” ANSV said. The agency recommends that EASA “define more stringent time limits” for the affected blades, and “re-evaluate the whole validity of the service management” Rolls used to minimize risk of blade failures.
ANSV also urged EASA to consider a de-pairing mandate that would not permit two engines with pre-modified-standard blades to operate on the same airframe. Such a provision existed early on, but when Rolls developed the new blade, it set life limits on older blades that were below the de-pairing threshold, and EASA dropped the mandate.
Aviation Week Fleet Data Services shows about 640 Trent 1000s in service, including 140 Trent 1000 TENs. Only about 3% of the fleet have the pre-modification-standard blades, Rolls said. Rolls is working to get those blades out of the fleet as quickly as possible, bringing forward planned swaps where possible.
"The early deterioration of IPT blades of this standard of blade is a known issue with an ongoing program of modification already agreed with EASA,” Rolls said. "We are working with our customers to accelerate the pace of this program.”
Rolls indicated that its blade life-limit calculation methods have “further evolved” and will be used to adjust Trent 1000 service strategies. It is not clear whether the changes will only affect the limited number of Trent 1000 pre-modification blades still flying, or will have wider implications.
“We respect the recommendations that have been published by the ANSV,” Rolls added. "We will continue to work closely with the Italian authorities to support their investigation, and with EASA as they consider the recommendations in the ANSV report.”
The IPT problems are one of a series of issues that have plagued Trent 1000 operators, leaving 787s grounded while engines undergo shop visits and wait on new or airworthy parts. Rolls has said it expects to spend a combined total of about $1 billion in mitigation measures in 2019 and 2020.