MAS Cargo B763 at Los Angeles on Jan 29th 2021, engine fire
Last Update: December 21, 2021 / 10:51:13 GMT/Zulu time
On Feb 1st 2021 the FAA reported: "AIRCRAFT EXPERIENCED AN ENGINE FIRE AND DIVERTED TO ONT, ONTARIO, CA." and rated the occurrence an incident stating the aircraft received "unknown" damage.
On Feb 2nd 2021 the NTSB reported they have opened an investigation into the occurrence though their investigators did not travel to the site. The NTSB stated: "experienced a right (No. 2) engine fire during climb from Los Angeles International Airport (LAX), Los Angles, California. A diversion to the Ontario International Airport (ONT), Ontario, California for an uneventful single engine landing was made."
On Dec 15th 2021 the NTSB opened their investigation docket and released their Aviation Incident Factual Report. The NTSB summarized the sequence of events:
The flightcrew reported feeling vibrations in the airplane as the landing gear was cycled up, so a second cycling of the gear was attempted, and the vibration continued. Shortly after that, the flightcrew detected a strong odor consistent with burning and a right engine fire warning message displayed on the engine indicating and crew alerting system (EICAS) display. The flightcrew declared an emergency, performed the Quick Reference Handbook (QRH) engine fire procedures, which included shutting down the affected engine and discharging 1 fire suppression bottle, and diverted to the Ontario International Airport (ONT), Ontario, California for an uneventful single engine overweight landing with no reported injuries to any of the flightcrew members.
The NTSB summarized the findings of the on scene examination:
The on-scene examination of the airplane revealed thermal distress and fire damage to the inside of the right engine core cowl and thrust reverser. The entire outer portion of the right engine turbine exhaust nozzle was missing as was the aft portion of the inner sleeve; the forward portion of the inner sleeve remained attached to the engine. The right engine strut/pylon outdoor skirt in-line with the aft edge of what remained of the turbine exhaust nozzle exhibited gouging and scratch marks. The airplane exhibited some impact marks and dings on the underside of the right wing and flaps, on the vertical and horizontal stabilizer, and on the right cargo door; however, some of the impacts appeared old and could not be confirmed if all the damage observed was from this incident.
The on-scene examination of the No. 2 engine revealed no signs of engine uncontainments but did show signs of low-grade thermal distress comprised of sooting and melted, consumed, and damaged cushion clamps, fire detector loop isolators, and electrical wire outer sheathing. Looking at the front of the engine, no damage was observed to the fan blades and the fan rotated freely by hand; the low pressure turbine rotated along with the fan. Looking through the engine exhaust:
1) all the low pressure turbine stage 5 blade roots were still installed in the disk and all the blades exhibited a combination of airfoil transverse fractures at various lengths and airfoil impact damage, tears, gouges, and missing airfoil material,
2) all the low pressure turbine stage 5 blade outer shroud segments were still present and exhibited a combination of gouging, missing material, heavy rub, and the honeycomb was worn down to the backing strip,
3) low pressure turbine stage 5 nozzles segments were present and exhibited a combination of trailing edge airfoil impact damage, gouges, tears, and missing material, and
4) the turbine rear frame exhibited a combination of multiple cracks, tears, openings, and punctures holes; no signs of low pressure turbine debris penetrating through the turbine rear frame skin was observed. The oil tank was low of oil and debris was noted on the magnetic chip detector. When the integrated drive generator was removed in preparation for transportation of the engine, a fractured oil supply line that runs from the aft side of accessory gearbox behind the integrated drive generator was observed. The No. 2 engine, engine serial number 695440, was removed and shipped to GE for disassembly and examination.
The engine underwent detailed inspection and metallurgic examination, the NTSB summarized the metallurgic findings:
The GE metallurgical analysis found the cracks and tears in the turbine rear frame and the turbine exhaust were due to overstress and no anomalies or pre-existing defects were noted that would have contributed to their condition. The fracture surfaces of the oil supply tube exhibited plastic deformation and a planar fracture consistent with secondary high amplitude fatigue/cyclic tensile loading. None of the low pressure turbine blade fracture surfaces showed signs of fatigue but features consistent with an overload failure. Signs consistent with high cycle fatigue growth were found on the fracture surfaces of airfoil Nos. 5 and 6 of the low pressure turbine stage 5 nozzle segment No. 3; the fatigue cracks propagated from both the leading and trailing edges of the missing airfoils. In the interpretable areas (not damaged area), GE found no material anomalies in the base material, aside from the areas of intergranular oxidation.
Low pressure turbine stage 5 nozzle segment No. 3, part number 9367M85P10, serial number HCM21194, had an extensive overhaul repair conducted in 2014 and has been in operational service for 10,232 hours and 4,068 cycles since the overhaul repair was performed. at the time of the event. Due to the leading and trailing edge impact damage on airfoils Nos. 5 and 6 of the low pressure turbine stage 5 nozzle segment No. 3 at the fracture locations, no determination could be positively made on whether a repair had been previously performed in that area, so no assessment of the repair conformity was made.
The Boeing metallurgical analysis of the turbine exhaust sleeve revealed that all the fractures were composed entirely of ductile separation fracture mode, consistent with a single event, and no other anomalies were observed contributing to the fractures.
On Dec 20th 2021 the NTSB released their final report concluding the probable cause of the incident was:
The fatigue fracture and liberation of two airfoils from a low pressure turbine stage 5 nozzle segment that impacted and damaged the downstream low pressure stage 5 blades creating an initial imbalance load in the engine’s low pressure turbine rotor sufficient to allow all the low pressure turbine blades to lose radial blade clearance, contact static structure, and to fracture transversely across the airfoil. The progressive failure of the low pressure rotor caused an increasingly imbalanced load that eventually resulted in the fracture of the oil supply tube that allowed oil to contact hot engine parts and smolder and ignite resulting in the undercowl fire.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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