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.'
