GE’s Ted Ingling helped develop the GE90-115B, the world’s largest and most powerful jet engine in service. Boeing uses the engine to power its 777 jets.
GE has recommended operators of GE90-115B engines install re-designed stator vane segments to prevent wear and potential cracking that investigators determined was behind a 2017 Japan Airlines (JAL) engine failure, a Japan Transport Safety Board (JTSB) report on the incident revealed.
The issue is linked to the spacing between the low-pressure turbine (LPT) fifth-stage stator segments. Tests conducted by GE in 2013 predicted that binding could cause adjacent segments in the 26-segment fifth-stage stator to wear, causing stress and potentially cracks in vanes.
Even though the issue had never been linked to an in-service incident, GE re-designed the segment to provide more clearance. GE introduced the change on the production line and made the new segment – which can be mixed with the original design – available for retrofit.
However, a service bulletin detailing the change “did not describe that the part was design changed as a countermeasure for the in-house test,” JTSB explained in its report.
On September 5, 2017, a JAL Boeing 777-300ER experienced No. 1 engine failure on takeoff from Tokyo International Airport en route to New York’s John F. Kennedy Airport. The crew shut the engine down and returned to Tokyo safely.
Investigators found one of the engine’s LPT fifth-stage stator vanes fractured, causing downstream damage including damaged turbine blades and a 6 cm by 1 cm (2.4 in. by 0.4 in.) hole in the turbine rear frame. The missing vane fragments were not recovered, but investigators linked the damage to the previously known wear condition, or “arch-binding,” JTSB said.
“Wearing caused by rubbing of adjacent segments was confirmed on … multiple segments of LPT fifth-stage stator vanes,” JTSB said, adding that “repetitive stress associated with engine operation” likely caused the crack on the failed vane to expand.
“It is highly probable that the serious incident was caused by collisions of some of the fragments with the turbine rear frame, which led to generating the hole due to damage to multiple stages of stator vanes and turbine blades of low-pressure turbine (LPT) of No. 1 (left side) engine immediately after take-off,” JTSB said.
“It is highly probable that damage to multiple stages of stator vanes and turbine blades of the low-pressure turbine was contributed by the fracture of one of LPT fifth stage stator vanes.”
GE issued an SB in July 2018 recommending borescope inspections for the affected area.
By April 2019, GE reported cracks and wear in 18 stator segments from 14 engines, including two operated by JAL. One of the JAL engines had an LPT fifth-stage stator with 25 original-spec segments and one new-spec segment. Signs of arch binding were found on all 25 of the original-spec segments, JTSB said.
GE in August last year issued an SB that recommended operators upgrade all original-spec stator segments when the LPT is disassembled, even if the segments do not need to be replaced. The JTSB report said it is “probable” that the change will reduce the likelihood of arch-binding.
The agency also urged GE to analyse its data and determine an “appropriate interval” for conducting inspections to monitor old-spec stator segments and advise operators.
JAL is inspecting its engines every 250 cycles, JTSB said.