Previous engine occurrences of this
aircraft
4 January 2002 (ATSB occurrence report
200200017)
During the landing flare shortly before touchdown, the aircraft
sustained a left engine flameout. The flight crew reported that the
engine exhaust gas temperature (EGT) remained high and selected the
left engine fuel control switch to the CUTOFF position and
completed the landing. After a visual inspection by fire crews at a
nearby taxiway, the aircraft was taxied to the terminal. The
operator's maintenance personnel inspected the engine for damage or
leaks, conducted idle and high power engine checks and completed
electronic engine control unlock function checks. All engine
parameters were found within limits and the aircraft was returned
to service.
5 January 2002 (ATSB occurrence report
200200006)
The B767 aircraft had just completed the landing roll, when air
traffic controllers in the tower noted fire coming from the left
engine. They advised the flight crew of the situation and called
for emergency services. The aircraft came to a stop on a nearby
taxiway. By the time emergency services arrived the fire had
extinguished. After a visual inspection by fire crews, the aircraft
was taxied to the terminal. Maintenance personnel conducted
troubleshooting using the engine manufacturer's troubleshooting
procedures. The left engine fuel control unit and fuel pump were
subsequently replaced. After completing test runs of the engine,
the aircraft was returned to service.
Engine/component history
On 14 December 2001, third party contract maintenance personnel
installed the left engine EVBC unit, part number 776555-7, serial
number F10363. At the time of installation, the operator reported
that the unit had accumulated 511,399 hours time since new, 506,732
cycles since new, 5,139 hours time since overhaul, and 3,315 cycles
since overhaul. The operator also advised that their practice was
to add 500,000 hours and cycles in order to identify units with
unknown hours and cycles prior to induction into their maintenance
control system. On 8 August 2001, the unit had been repaired by the
manufacturer following removal to resolve a discrepancy of a thrust
lever split, inability to close the 3.0 bleed valve and an EGT
difference between engines of 120 degrees C.
On 30 December 2001, the engine was test run for three hours.
The results of the engine run were documented and plotted on the
appropriate engine documentation graphs. Those plots were examined
and considered within prescribed limits. Having met all applicable
parameters, the engine and aircraft were subsequently returned to
service.
Following the 8 January 2002 occurrence, a review of the plotted
data on the engine run sheets indicated that several plotted points
fell slightly within the lower limits of the acceptable trim band.
The EVBC was initially bench tested at the operator's facility but
failed the testing and was then sent to the manufacturer for
further examination. The operator reported that the manufacturer's
testing confirmed that the EVBC and bleeds were operating out of
tolerance. The unit was subsequently disassembled and
overhauled.
Engine stall or surge
Gas turbine engines, under certain operating conditions, may
stall or surge due to any condition where the flow of air from the
compressor's inlet to its outlet was disturbed. This can result in
uncommanded shutdowns, internal damage or reduced performance of
the engine.
Engine compressor control system
The engine compressor control system (air scheduling) increased
compressor stability during engine starts, transient and reverse
thrust operations. The variable geometry stator vanes regulated
airflow into and through the high-pressure compressor. At maximum
power settings, the variable stator vanes were actuated to their
maximum open position to permit the greatest airflow to the engine.
At that time, during normal operation, the start bleed valves
(controlled by a signal from the EVBC to the normally open bleed
ring) were fully closed so that the compressor discharge air was
delivered to the combustor and turbine sections.
During power reductions for landing, the engine compressor air
scheduling to the left engine was incorrect. That resulted in
disrupted airflow throughout the engine and subsequent stalling.
The discrepancy in the air scheduling of the engine was due to the
incorrect performance of the engine vane bleed control unit. This
anomaly could also have resulted in excessive amounts of fuel for
the power setting and contributed to the fire witnessed coming from
the left engine exhaust as reported during the 5 January 2002
occurrence on this aircraft (see ATSB report 200200006).
Local safety action
As a result of this occurrence, the third party maintenance
organisation advised, 'As a preventative measure we have briefed
our maintenance personnel to trim or adjust to mid band position
when trimming or adjusting to a given band.'