Incident: JAL B773 at Tokyo on Sep 5th 2017, engine shut down in
flight following uncontained failure
A JAL Japan Airlines Boeing 777-300, registration JA743J performing
flight JL-6 from Tokyo Haneda (Japan) to New York JFK,NY (USA) with 233
passengers and 18 crew, was in the initial climb out of Haneda's runway 34R when
the left hand engine (GE90) emitted a series of 5 bangs and streaks of flame.
Tower informed the crew about seeing flames out of the engine. The crew
receiving abnormal indications for engine #1 stopped the climb at 6000 feet,
shut the engine down, dumped fuel and returned to Haneda for a safe landing on
runway 34L about one hour after departure.
Metal debris was found on the departure runway.
A replacement Boeing 777-300 registration JA741J is estimated to
reach New York with a delay of 6.5 hours.
The airline initially suspected a bird strike but later reported that
no bird remains were found. The cause of the engine failure is under
investigation.
Japan's Ministry of Transport reported the grass left of the
departure runway caught fire when the engine distributed debris onto the runway.
An inspection of the engine did not reveal any bird remains. A number of blades
of the low pressure turbine were missing.
On Sep 7th 2017 Japan's TSB rated the accident type as: "Things
similar to 'breakage of the engine (only when the debris penetrates the case of
the engine)'" effectively describing the engine failure was uncontained. The
JTSB have opened an investigation.
On Nov 29th 2019 the JTSB released their final report concluding the
probable causes of the serious incident were:
It is highly probable that the serious incident was caused by
collisions of some of fragments with turbine rear frame (TRF), 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.
It is highly probable that damage to multiple stages of stator vanes
and turbine blades of low pressure turbine was contributed by the fracture of
one of LPT fifth stage stator vanes.
It is highly probable that the fracture of one of LPT fifth stage
stator vanes was contributed by the crack generated by stress concentration
caused by arch-binding, which progressed to the fracture by repetitive stress
associated with engine operation.
The JTSB reported immediately after becoming airborne noise was
generated by the #1 engine, the engine rpms decreased and a caution message "ENG
THRUST L" was displayed on the EICAS. Tower observed flames from behind the
engine. The crew proceeded to shut the engine down, declared emergency, dumped
fuel and returned to Tokyo for a safe landing. Engine fragments were recovered
from the departure runway and its surroundings, a grass area near the departure
runway was burned, the grass fire needed to be extinguished by emergency
services.
The JTSB analysed the engine damage:
(1) Damage on LPT
(i) It is highly probable that damages on fifth and sixth stage
turbine blades which were downstream from LPT fifth stage stator vanes were
triggered by fracture of one stator vane of the fifth stage stator vanes
segment, then collisions of fragments with fifth stage turbine blades led to
further damage, and continuous collisions of those fragments with other sections
resulted in the secondary damage.
(ii) Fracture of LPT fifth stage stator vane
It is highly probable that the fractured fifth stage stator vane was
impelled to be supported only by the inner side of engine due to the crack which
reached from the trailing edge side to the leading edge side caused by
repetitive stress associated with operations of engine, followed by another
crack generating and progressing on inner side of engine, which finally resulted
in fracture, because many striations indicating fatigue fracture were confirmed
on the fractured surface of the outer side of engine of LPT fifth stage stator
vane segment.
It is probable that the crack of LPT fifth stage stator vane was
caused by increased stress on the trailing edge side of LPT fifth stage stator
vane caused by arch-binding, because wearing, which was a trace of arch-binding,
was confirmed on the slash-face of LPT fifth stage stator vane segment on the
inner side of engine and arrest lines were periodically confirmed through
fracture analysis.
(2) The Hole of TRF
It is highly probable that the hole of TRF was caused by collisions
of fragments generated by the damaged LPT.
It is probable that fragments did not penetrate the hole, because
analytical results by NIMS and engine cowl did not show damage.
(3) Flame Outbreak at Engine Aft
It is highly probable that the flame that occurred at the engine aft
became incomplete combustion by the change in mixing rate in air flow amount and
fuel flow amount after the engine rpm had deviated from normal operating
condition due to the damage occurred in LPT, and then, the after fire occurred
due to the mixed gas including the fuel was exhausted to the engine aft and was
rapidly burned by the supply of oxygen in the atmosphere along with the heat of
exhaust duct, because evidence of abnormal combustion inside the engine was not
confirmed.
(4) Burned Grass Area along the Side of Runway
It is probable that burned grass area was caused by high temperature
fragments exhausted from the engine aft due to damage of LPT and fell on the
grass area on the side of runway near the taking off area of the
Aircraft.
(5) Safety Actions to Avoid Similar Cases
Inspection conducted by the Operator and the engine manufacturer
after the serious incident confirmed that cracks and wearing caused by
arch-binding occurred in multiple segments of LPT fifth stage stator
vanes.
In the serious incident, there occurred the ground damage of burning
grass area caused by many fragments of damaged multiple stages of LPT stator
vanes and turbine blades, which fell on runway and its surroundings. From this,
it is probable that taking safety actions as described below is meaningful to
prevent similar engine failure cases and falling objects on the ground in the
future:
(i) Widening space between adjacent segments of LPT fifth stage
stator vanes Cracks and wearing caused by arch-binding were confirmed to have
occurred on multiple segments of LPT fifth stage stator vanes since the serious
incident.
It is probable that widening space between adjacent segments of LPT
fifth stage stator vanes, which has not changed design in accordance with the
service bulletin (SB72-0637), reduces stress increase to the outer side of
engine of LPT fifth stage stator vanes caused by arch-binding and contributes to
prevent occurrence of cracks in fifth stage stator vanes. It is probably
meaningful to widen space between adjacent segments by use of LPT fifth stage
stator vanes in accordance with the service bulletin (SB72-0637) or by
modification of segments to which the service bulletin (SB72-0637) has not been
applied in order to avoid recurrence of similar cases.
(ii) Inspection of LPT fifth stage stator vanes segments
It is probable that BSI is effective for early detection of similar
engine failure, because the cracks were confirmed on LPT fifth stage stator
vanes of multiple engines by one time BSI on each engine at the engine
maintenance facility after the serious incident, and furthermore, the cracks
were confirmed on LPT fifth stage stator vanes of multiple engines by the BSI
which the Operator has been conducting every 250 flight cycles on the same type
engines under operation. Accordingly, it is desirable that the engine
manufacturer notify the users of the same type engine of the method of BSI and
an appropriate interval to repeat BSI for the segments of LPT fifth stage stator
vanes, which have not taken countermeasure to widen space between adjacent
segments of LPT fifth stage stator vanes on engines under operation by service
bulletin (SB).
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