Situations, connected with aviation fuel can be extremely dangerous during the flight.
1. Fuel contamination.
Aviation fuel undergoes several tests before being put into an aircraft. Still it always contains little particles of water and some special chemicals to prevent it from freezing. During the wintertime possibility of fuel thickening gets much higher.
British Airways Flight 38 was a scheduled flight operated by a British Airways Boeing 777 from Beijing which crash landed just short of the runway at its destination, London Heathrow Airport, on 17 January 2008. There were no fatalities but 47 people sustained injuries.
\"\"Ice crystals in the fuel were the cause of the accident, clogging the fuel-oil heat exchanger (FOHE) of each engine. This restricted fuel flow to the engines when thrust was demanded during the final approach to Heathrow. Boeing identified the problem as specific to the Rolls-Royce engine fuel-oil heat exchangers, and Rolls-Royce subsequently developed a modification to its FOHE; the European Aviation Safety Agency (EASA) mandated that all affected aircraft were to be fitted with the modification before 1 January 2011. Boeing 777 aircraft powered by GE or Pratt & Whitney engines were not affected by the problem. Flight 38\’s route took it over Mongolia, Siberia and Scandinavia, at an altitude which varied between 34,800 and 40,000 ft (10,600 and 12,200 m), and in temperatures between -65 and -74°C. Aware of the cold conditions outside, the crew monitored the temperature of the fuel, with the intention of descending to a lower, warmer, level if there was any danger of the fuel freezing. In the event, this did not prove necessary, as the fuel temperature never dropped below -34°C, still well above its freezing point.
Although the fuel itself did not freeze, small quantities of water in the fuel did. Ice adhered to the inside of the fuel lines, probably where they run through the struts attaching the engines to the wings. This accumulation of ice had no effect on the flight until the final stages of the approach into Heathrow, when increased fuel flow and higher temperatures suddenly released it back into the fuel. This formed a slush of soft ice which flowed forward until it reached the FOHEs where it froze once again, causing a restriction in the flow of fuel to the engines.
The first symptoms of the fuel flow restriction were noticed by the flight crew at 220 m of height and 3.2 km of distance from touchdown, when the engines repeatedly failed to respond to a demand for increased thrust from the autothrottle. The autopilot disconnected at 46 m, as the co-pilot took manual control. Meanwhile, the captain reduced the flap setting from 30 degrees to 25 degrees in order to decrease the drag on the aircraft and stretch the glide. The plane landed on the grass approximately 270 metres short of runway 27L. The captain declared an emergency to the control tower a few seconds before landing.
During the impact and short ground roll, the nose gear collapsed, the right main gear separated from the aircraft penetrating the central fuel tank and cabin space, and the left main gear was pushed up through the wing. The aircraft came to rest on the threshold markings at the start of the runway. A significant amount of fuel leaked, but there was no fire.
2. Fuel starvation.
\"\"On 21st August 1963 Aeroflot\’s Tupolev Tu-124, performing a regular flight with 45 passengers and  7 crew on board from Tallinn to Moscow diverted to Leningrad due to nose gear malfunction. In order to expend some fuel, reducing weight and decreasing risk of fire during forced landing, the aircraft started to circle over Leningrad at 500 m.  Each loop in the airspace around the city took the aircraft approximately 15 minutes. During this time the crew attempted to force the nose gear to lock into the fully extended position. The crew got carried away and didn\’t notice how after 2 hours fuel ran out. Upon loss of power to both engines, the only hope was to ditch the aircraft in the 400-metre-wide Neva River. Eyewitnesses saw the airplane descend upstream along the river. Immediately after the turn, the craft glided over the high steel structures of the Bolsheokhtinsky Bridge with approximately 30 m of clearance. Tu-124 flew just over the Alexander Nevsky Bridge — under construction at the time — barely missing it. The pilot managed to ditch the aircraft onto the river surface. Passengers and crew then evacuated the cabin via an access hatch on the plane\’s roof, no one was seriously hurt.
\"\"The Gimli Glider is the nickname of an Air Canada aircraft that was involved in an unusual aviation incident. On July 23, 1983, Air Canada Flight 143, a Boeing 767, ran out of fuel at FL 410 (12,000 m), about halfway through its flight from Montreal to Edmonton. The crew were able to glide the aircraft safely to an emergency landing at a former Royal Canadian Air Force base in Gimli, Manitoba.
The subsequent investigation revealed company failures and a chain of human errors that combined to defeat built-in safeguards. Fuel loading was miscalculated due to a misunderstanding of the recently adopted metric system which replaced the imperial system. Instead of 22,300 kg of fuel, they had 22,300 pounds on board — 10,100 kg, about half the amount required to reach their destination.
\"\"Air Transat Flight 236 was an Air Transat flight from Toronto to Lisbon, that lost all power while flying over the Atlantic Ocean on August 24, 2001. The Airbus A330 suffered a complete power loss due to a fuel leak caused by improper maintenance. Captain Robert Piché, 48, an experienced glider  pilot, and First Officer Dirk de Jager, 28, flew the plane to a successful emergency landing in the Azores, saving all 306 people on board.
Leaving the gate in Toronto, the aircraft had 46.9 tonnes of fuel on board. 4 hours after departure, a cockpit warning system chimed and warned of low oil temperature and high oil pressure on engine #2. There was no obvious connection between an oil temperature or pressure problem and a fuel leak. Consequently Captain Piché, suspected they were false warnings.
\"\"Several minutes later the pilots received a warning of fuel imbalance. Not knowing at this point that they had a fuel leak, they followed a standard procedure to remedy the imbalance by transferring fuel from the left wing tank, to the near-empty right wing tank.
Starting to realize they had the serious problem, the pilots decided to divert to Lajes Air Base in the Azores, declaring a fuel emergency. At 10000 m still 120 km from Lajes both engines flamed out and stopped because of fuel starvation.
The aircraft lost its main hydraulic power, which operates the flaps, alternate brakes, and spoilers. The descent rate of the plane was about 2,000 feet (600 metres) per minute. They calculated they had  about 15 to 20 minutes left before they would be forced to ditch in the ocean. The air base was sighted a few minutes later. Captain Piché had to execute one 360 degree turn, and then a series of \»S\» turns, to dissipate excess altitude.
19 minutes later the plane touched down hard, at a speed of approximately 200 knots (370 km/h). Since they had lost the anti-skid and brake modulation systems, the eight main wheels locked up; its tires abraded and fully deflated within 450 feet (140 m). Fourteen passengers and two crew members suffered minor injuries, while two passengers suffered serious injuries during the evacuation of the aircraft. The plane suffered structural damage to the main landing gear and the lower fuselage.

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