Abstract
Understanding the cause of a crash is important in ensuring that similar occurences do not persist in future. The airlines industry worldwide has been undergoing postmortem after accident to ensure that safety and crashes are reduced drastically. The causes of crashes are diverse in nature, varying from manufacture to takeoff and landing. Investigators of accidents look into all these factors to deduce reason of crash of the plane. This research focuses specifically on the turbine engine investigation of British airline accident. The plane in focus was scheduled for travel between Beijing, China and London on January 17 th 2008 at 12:42 GMT having completed 8,100-kilometre trip.
Being the first Boeing 777-200ER to incur losses in history, the airplane caused injuries for 47 people out of the 152 passengers onboard the flight. After investigation, the cause of the accident was identified as ice crystals which were in the fuel overflowing to the fuel oil heat exchanger (FOHE) of each engine. Investigations led to modification of the FOHE as a mandate from European Aviation Safety Agency before January 1 st , 2011. The Air Accident Investigation Branch also studied the crashworthiness of the aircraft during the accident sequence. It observed that the main attachment point for the main landing gear (MLG) was the rear spar of the aircraft's wing. The findings recommended that Boeing redesign the landing gear attachment to reduce the likelihood of fuel loss in similar circumstances.
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Introduction
British airways flight 38 was a scheduled flight operated by British Airways from Beijing, China to London, United Kingdom. It crashed shortly before arriving at its destination on January 17 th , 2008 at 12:42GMT having completed 8,100-kilometre trip. Out of the 152 people who had boarded the flight, 47 had injuries of which one of them was serious. This was the first Boeing 777-200ER to incur total loss in their history. It was a 150 ton aircraft (Hendrecky, 2010) .
The cause of the accident was said to be ice crystals which were in the fuel overflowing to the fuel oil heat exchanger (FOHE) of each engine. It restrained the flow of fuel to the engines when the operation was demanded during the last approach to Heathrow. They identified the problem as specified to Rolls-Royce engine fuel-oil exchangers and they came up with a modification of their FOHE. All the affected aircrafts were to be fitted with a modification as a mandate from European Aviation Safety Agency (EASA) before January 1 st , 2011.
Accident
The serial number of the manufacturer was 30314, line number 342 an aircraft used for the flight Boeing 777-236ER G- YMMM powered by Rolls-Royce Trent 895-17 engines. This aircraft first flew on the May 18 th , 2001. It was delivered to British Airways on May 31 st ; 2001. This aircraft had a seating capacity of 233 passengers. During the specific trip, the aircraft route passed over Siberia, Scandinavia and Mongolia. The altitude ranged between 34,800 and 40,000 feet and temperatures between -65 and -74 degrees Celsius. The fuel temperatures were monitored by the crew because it was extremely chilly outside. The fuel temperatures never dropped to -34 degrees Celsius which was still above its freezing point. Little quantities of water in the fuel froze though the fuel itself did not. The ice ran through the struts linking the engines to the wings. The ice accumulation had no consequence till the aircraft’s last stages of approach to Heathrow. Due to the increase of its oil flow, high temperatures got it back in to the fuel. It formed soft ice hence flowing forward until it reached the fuel-oil heat exchangers and froze again. This caused a constraint in the flow of the fuel to the engines.
Fuel restriction was first noticed by the crew at the height of 720feet and two miles from touchdown. The engines repeatedly failed to the demand for increased pressure from auto-throttle. In an attempt to maintain the ILS (instrument landing system) glide slope, the pilot sacrificed speed. The co-pilot took manual control. The flap setting was reduced from 30 degrees to 25 degrees in order to stretch the glide. The plane landed on a grass approximately 270 meters from runway. An emergency was declared to the control section by the captain few seconds before landing. The nose gear collapsed due to the impact and the ground roll. The left main gear was propelled upwards through the wing while the main gear caused to move from the aircraft penetrating the cabin space and the central fuel tank. Some amount of fuel leaked though there was no fire. One passenger sustained serious injuries and few others sustained minor injuries.
Causes
An investigation given by AAIB identified probable cause factors that led to the fuel flow restrictions. Requirements of certification which engine fuel system and aircraft had to comply didn’t take account to this phenomenon as the risk was not recognized at that time .The FOHE was restricted when soft ice was formed in the fuel. Ice from within the system restricted fuel flow at the face of FOHE on both engines.
FUEL SYSTEMS
The report noted that the plane had flown through air that was extremely cold, but came to a conclusion that the temperature was not low enough to freeze the fuel. Another examination and analysis was to be done on the entire aircraft and engine fuel systems which included modeling fuel flows, taking account of aerodynamic and environmental effects (Murray, Broadley, & Morris, 2011) .
Air Accident Investigation Branch (AAIB) later said that the investigations were still being focused on fuel delivery. It further said that the reduction in thrust on both engines was brought about by decreased fuel flow. All engine parameters after the force reduction were consistent with this. Fuel freezing was ruled out as a cause of the crash. They stated that fuel was of good quality and of freezing point below the chilled temperatures. They also reported of the damage to the high pressure fuel pumps of the engines and also indicated of abnormal low force at the pump inlets (Kinnersley & Roelen, 2007) . The fuel delivery system was being investigated at Boeing and engines at its manufacturer’s (Rolls Royce) point in Derby.
Conclusion
An interim report was issued by AAIB on September 4 th which stated that the fuel to both engines was restricted due to the ice formed in the fuel feed system (Sleight & Carter, 2010) . It was most probable that the ice was formed from water mixed in the fuel while the aircraft operated for extended periods in extremely cold weather without decreased fuel flow (Branch, 2008) . Nevertheless, the G-YMMM was operated in the range of certification at all times. They further stated that may be ice had accumulated which caused a blockage at some point or ice had become dislodged through the fuel lines as fuel flow increased during landing approach and the clogged ice had formed blockage at some point in the downstream.
It was also recommended that FAA and EASA (aviation regulators) should consider whether other aircraft engines and types can be affected by the same predicament. They also majored on change of certification process in order to ensure future aircraft designs would not be affected by any kind of danger from ice formed in the fuel.
References
Branch, A. A. (2008). Interim Report: Accident to Boeing 777-236ER. G-YMMM at London Heathrow Airport , 17.
Hendrecky, S. (2010). Report: British Airways B772 at London on Jan 17th 2008, both engines rolled back on final approach . Retrieved September 27, 2017, from The Aviation Herald: http://avherald.com/h?article=4270d893
Kinnersley, S., & Roelen, A. (2007). The contribution of design to accidents. Safety Science, 45(1) , 31-60.
Murray, B. J., Broadley, S. L., & Morris, G. J. (2011). Supercooling of water droplets in jet aviation fuel. Fuel, 90(1) , 433-435.
Sleight, P. A., & Carter, R. D. (2010). Report on the accident to Boeing 777-236ER, G-YMMM, at London Heathrow Airport on 17 January 2008. London, UK: Air Accidents Investigation Branch, Department of Transport (UK).
