British Airways B772 at Las Vegas on Sep 8th 2015, rejected takeoff due to engine fire, engine failure uncontained
Last Update: June 21, 2018 / 15:11:41 GMT/Zulu time
Las Vegas Airport reported flames were spotted at 16:14L (23:14Z), the fire was put out by 16:18L. Two occupants were taken to hospitals for minor injuries, a total of seven needed medical attention.
Emergency services reported a total of 13 occupants required medical treatment.
The FAA reported on Sep 9th 2015 that the left hand engine caught fire during the departure roll, aircraft stopped on the runway and was evacuated via slides, 5 persons received unknown injuries. The aircraft was substantially damaged, the occurrence was rated an accident.
Passengers reported there was a loud bang from the left hand side, the brakes came on, then there was enormeous heat, that appeared to melt down a couple of passenger windows, smoke entered the aircraft. They evacuated down the slides and were taken to the terminal. Later the captain joined the passengers at the terminal and told them, that they had suffered a catastrophic failure of the left hand engine.
A planespotter from Salzburg (Austria) visiting Las Vegas reported, that he was watching aircraft at Las Vegas Aerodrome at East Sunset Road, below the approach path to runways 07. He took notice of the Boeing 777-200 when it taxied towards the holding point runway 07L because there were not many heavies around. The Boeing appeared to be taxiing rather slowly, lined up normally, engines accelerated normally and the aircraft was about 200-300 meters/600-1000 feet into the departure roll when a large streak of fire and dense smoke was emitted by the left hand engine, without any noise. The aircraft slowed and came to a stop, dense black smoke rising from the aircraft.
The airline reported: "The aircraft, a 777-200 experienced a technical issue as it was preparing for take-off from McCarran International Airport in Las Vegas. Our crew evacuated the aircraft safely and the fire was quickly extinguished by the emergency services at the airport. 157 customers were on board the flight, along with three pilots and 10 cabin crew. A small number of customers and our crew have been taken to hospital." The passengers were taken to hotels, hotlines have been opened for friends and relatives of those on board.
The NTSB have dispatched three investigators on site.
The runway was closed for 4 hours, the FAA issued ground stops for a number of flights inbound to Las Vegas.
On Sep 10th 2015 the NTSB reported first preliminary findings. The NTSB reported that there were multiple breaches of the engine case in the area of the high pressure compressor, several pieces of the high pressure compressor spool were found on the runway. The engine, engine pylon, fuselage structure and the inboard left wing were substantially damaged by fire. A number of occupants received minor injuries, mainly abrasions, in the evacuation. Cockpit Voice, Flight Data and Quick Access recorders have been taken to the NTSB Laboratory and are being downloaded.
On Sep 15th 2015 media reports started to surface claiming that the FAA had made links between an Airworthiness Directive (AD) FAA-2010-1024 issued by the FAA in 2011 concerning a weld joint between 9th and 10th stage of the HPCR spool 8-10, where cracks had been discovered during examination of an engine, the FAA rated that condition as potentially unsafe and required additional inspections of GE90-76B, GE90-77B, GE90-85B, GE90-90B and GE90-94B engines. General Electric states however, that the BA B772 was equipped with different parts, for which this AD FAA-2010-1024 is not applicable.
On Oct 2nd 2015 the NTSB released their preliminary report reporting that there was one serious and 5 minor injuries as result of the evacuation following an uncontained #1 engine failure resulting in a fire damaging the #1 engine, inboard left wing and portions of left and right fuselage.
On Oct 6th 2015 the NTSB reported that first examination of the engine revealed that the stage 8-10 spool in the high pressure compressor (HPC) had failed liberating fragments that breached the engine case and cowling. Additional pieces of the HPC were found inside the engine and sent for metallurgic examination. The fracture began in the stage 8 disk web.
On Apr 12th 2017 the NTSB opened their public docket. The documents available suggest that the crew reacted within one second after the left hand engine's N2 dropped from stable 113% to 98% with increasing fuel flow. The #1 engine fuel cut off lever was moved to off within one second, the right hand engine's thrust lever was brought to idle at the same time. 6 seconds after the N2 dropped the engine fire warning became active followed by a engine #1 overheat warning. The aircraft came to stop, the crew radioed their were stopping and initiated the engine fire checklist. The crew announced to the passengers to remain seated. 26 seconds after the captain called "STOP" the crew radioed Mayday and requested fire services. Smoke was observed on board of the aircraft, however, it was believed for some time the fire had gone out. 150 seconds after N2 dropped the captain instructed the cabin to evacuate right hand side, 4 seconds later the crew informed ATC about the evacuation. 192 seconds after N2 dropped a forward cargo smoke warning became active. The crew discussed engine shut down checklists and evacuation checklists and read the evacuation checklist (until end of CVR recording).
The powerplant group reported in their chairman's report:
The pieces of the high pressure compressor recovered on site were first sent to the NTSB material laboratory for initial metallurgical examination. The received pieces accounted for less than 50% of the stage 8 outer rim. One of the recovered pieces with the dovetail slot and forward seal teeth still attached exhibited a hemi-elliptical shaped flat-fracture region that initiated in fatigue on the aft face of the web and transitioned circumferentially in both directions. A field emission scanning electron microscope was used to examine the surface in greater detail and the fracture region revealed an intergranular appearance near the initiation site and striations in the transgranular region of the fracture where striation density measurements could be taken to estimate the number of flight cycles from initiation/detection to failure. The NTSB materials laboratory estimated the number of flight cycles from detection to separation to be approximately 5,400 cycles. The last inspection of the event high pressure compressor spool was conducted by GE Wales 3,943 cycles prior to the failure.
After the initial examination of the high pressure compressor stage 8 pieces by the NTSB materials laboratory, they were sent to the GE Aviation Material Laboratory for further evaluation along with the stage 8 disk that was removed during the engine disassembly. Over several weeks, persons from the NTSB and FAA participated and oversaw much of the additional examination and testing. With all the recovered parts of the high pressure compressor stage 8 disk put together, it appeared that the entire disk rim and web was accounted for. GE’s analysis of the stage 8 disk concluded: 1) the crack initiation propagated with intergranular features with local variations consistent with hold-time, high-alternating stress, low cycle fatigue (hold-time low cycle/sustained-peak, low cycle) consistent with the NTSB finding, 2) no microstructural anomalies or detrimental species in the grain boundaries were found near the fracture origin, 3) the material composition, hardness, and grain structure were as specified, 4) multiple secondary cracks were found, but only within 0.016 inches radially of the fatigue region, 5) just like the primary fracture, no microstructural anomalies were found at the secondary crack locations, and 6) the shot peening appearance on the forward web face had more pronounced peening dimples than the web aft face. GE also performed their own striation density calculation and they estimated the number of flight cycles from detection to separation to be between approximately 5,000 – 5,700 cycles, consistent with the NTSB finding.
In order to better understand how the crack could have initiated in the web of the stage 8 disk, GE performed a series of additional hardware testing (for example residual stress and strain distortion), computational analysis (reevaluated the LCF lifing based on the actual event hardware, including all the material review board accepted allowable deviations and under the worst material property conditions) and operation mission profile review (verify stresses during taxing time, takeoff thrust rating, shutdown, core speeds and temperatures, ambient takeoff temperature, etc.). All the predictive calculations that GE performed could not close on the event crack location at the number of cycles it was thought to have initiated the crack; however, the striation density curves that were developed for the event spool match well with the analytical predictive crack propagation rate.
Based on this event, GE developed and incorporated into the engine maintenance manual a set of unique non-destructive inspections for the HPC stage 8-10 spool focusing on the event crack location. These inspections can be performed at the piece part, rotor and module levels, as well as on-wing. Along with the addition of the engine manual non-destructive inspections, GE released three separate service bulletins (SB 72-1145, SB 72-1146, and SB 72-1151) to inspect all the GE90 HPC stage 8-10 spools with part number 1694M80G04 (failure event spool part number) and a selected number of spools part numbers 1844M90G01 & G02. The Federal Aviation Administration mandated those inspections by issuing airworthiness directives AD 2015-27-01 and AD 2016-13-05.
On Jun 20th 2018 the NTSB released their final report concluding the probable cause of the accident was:
The failure of the left engine high-pressure compressor (HPC) stage 8-10 spool, which caused the main fuel supply line to become detached from the engine main fuel pump and release fuel, resulting in a fire on the left side of the airplane. The HPC stage 8-10 spool failed due to a sustained-peak low-cycle fatigue crack that initiated in the web of the stage 8 disk; the cause of the crack initiation could not be identified by physical inspection and stress and lifing analysis. Contributing to this accident was the lack of inspection procedures for the stage 8 disk web.
The NTSB analysed that a "bang" sound was heard in the cockpit followed by an aural announciation "engine fail" via the EICAS. The captain moved the thrust levers to idle at about 77 knots, two seconds after the bang, and rejected takeoff bringing the aircraft to a stop 15 seconds after the bang. The NTSB wrote: "Thus, the captain made a timely decision to reject the takeoff and performed the maneuver in accordance with company training and procedures."
The NTSB analysed that the engine manufacturer predicted the aft web face would endure about 30,000 cycles before crack initiation than the actual engine, which had accumulated 11,459 cycles, the cracks causing the accident had developed over about 5400 cycles starting at about cycle 6000. The NTSB wrote: "GE was unable to determine why a crack initiated via sustained-peak low-cycle fatigue in the disk web. GE has not previously experienced environmental cracking under the operational conditions to which the stage 8 disk web was subjected and GE's postaccident inspections of additional HPC stage 8-10 spools did not find any cracks in any other disk webs. Further inspection of the accident stage 8 disk did not find additional cracks in the web (other than secondary cracks in the immediate area of the crack that led to the disk failure). The disk web was not an area that required routine inspections, so the crack on the accident disk went undetected."
With respect to the evacuation the NTSB analysed:
While the airplane was decelerating to a stop, the fire warning bell sounded. When the airplane came to stop, the captain called for the engine fire checklist. The third item on the checklist was to move the fuel control switch on the affected side (in this case, the left side) to the cutoff position, which shuts down the respective engine. The spar valve terminates fuel flow to an engine after it is shut down. Flight data recorder (FDR) data showed that about 28 seconds elapsed between the start of the engine failure and the time of the spar valve closure, and Boeing estimated that about 97 gallons of fuel had spilled onto the runway during this time. FDR data also showed that 22 seconds elapsed between the time that the captain initially called for the engine fire checklist and the time of the spar valve closure. (Thirteen seconds had elapsed between the time that the captain repeated his call for the engine fire checklist and the time of the spar valve closure.) If the left engine had been shut down sooner, there would have been less fuel on the runway to feed the fire.
The flight crew informed the passengers and flight attendants to remain seated and await further instruction, which was consistent with the flight crew's training and procedures if an evacuation was not going to immediately occur. The cabin crew reinforced the flight crew's expectation by instructing passengers to remain seated. As part of the flight crew's evaluation of the situation, the relief pilot left the cockpit and entered the forward cabin so that he could look outside a window. Before the relief pilot returned, the CVR recorded the captain's statements indicating that the airplane should be evacuated. The relief pilot returned to the cockpit shortly afterward and informed the captain of the need to evacuate on the right side of the airplane because of the fire. The captain then commanded the evacuation, and a flight crewmember activated the evacuation alarm.
When the relief pilot went into the cabin to assess the situation outside of the airplane, a flight attendant told him that she had been trying to call the flight crew. The CVR recorded a sound similar to an interphone call from the cabin to the flight deck, but the flight crewmembers most likely did not answer the call because they were focused on securing the left engine and deciding whether to evacuate.
After the captain's evacuation command, the flight attendants assessed their areas and opened the doors that they deemed usable. Five of the eight door exits were initially blocked by flight attendants, which was appropriate given the hazards associated with the smoke, fire, and unusual attitude of two slides. A sixth door, which was initially opened, was blocked once a flight attendant saw flames on the runway, which was also appropriate. Although only two of the eight door exits were used throughout the evacuation, the passengers and crewmembers were able to evacuate before smoke and fire encroached the fuselage.
The captain commanded the evacuation (step three in the evacuation checklist) before calling for the evacuation checklist and performing the first two steps in the checklist. Step two of the evacuation checklist instructs the captain to shut down both engines. The left engine was shut down as part of the engine fire checklist, but the right engine continued operating for about 43 seconds after the captain's evacuation command. The unusual attitude of two slides (the 3R and 4R slides) resulted from the jet blast coming from the right engine while it was operating.
The captain did not use the QRH to read and do his evacuation checklist items. The right engine was shut down after the relief pilot noticed EICAS indications showing that the engine was still running. Also, the captain's call for the evacuation checklist occurred after the relief pilot stated that the checklist needed to be performed. (The first officer had stated, just before the relief pilot, "we haven't done the engine checklist," but he most likely meant the evacuation checklist.) Because the captain did not follow standard procedures, his call for the evacuation checklist and the shutdown of the right engine were delayed.
With respect to passengers carrying their carry ons during evacuation the NTSB analysed:
During a group debriefing by the Air Accidents Investigation Branch, the flight attendants stated that some passengers evacuated with carry-on baggage; however, the flight attendants thought that carry-on baggage retrieval did not slow the evacuation. They thought that most passengers who retrieved baggage did so after the airplane came to a stop and before the evacuation was commanded and that the flight attendants' assertive commands limited further retrieval. The flight attendants at the two most-used exits (doors 1R and 4L) recalled seeing very little baggage at their exits, and neither cited carry-on baggage as a problem. However, the NTSB notes that the accident airplane was only 55% full.
Although not a factor in this evacuation, the NTSB remains concerned about the safety issues resulting from passengers evacuating with carry-on baggage, which could potentially slow the egress of passengers and block an exit during an emergency. The NTSB previously addressed carry-on baggage in a June 2000 safety study on evacuations of commercial airplanes and issued Safety Recommendation A-18-9 in February 2018 as part of its final report on the American Airlines flight 383 investigation.
ABC News coverage including onboard passenger video, seconds 32-50 (Video: ABC News)
Video of a passenger on another flight (Video: Ravi S):
Video of a passenger in the terminal (Video: Balaji Rajgiri)
This article is published under license from Avherald.com. © of text by Avherald.com.
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