The Air Accidents Investigation Branch (AAIB) issued on Sept. 4 an interim report concerning concerning the accident to the British Airways Boeing 777-236ER, G-YMMM that crash landed short of RWY 27L at London Heathrow airport on Jan 17, 2008.
According to the report, that can be downloaded at the following address (http://www.aaib.dft.gov.uk/publications/interim_reports/boeing_777_236er__g_ymmm.cfm) the engines lost power during the final phase of the approach because ice accumulated next to the engine fuel feed system. The ice probably formed because water (naturally) existing in the fuel dropped below the water’s freezing temperature. Even if the aircraft operated within the certified envelope, the temperature recorded during the flight from Beijing to London, was lower than usual.
Aviation fuel contains water. Fuel tanks usually have low percentages of fuel below the freezing point of water because it is impossible to drain all the water out of them. So, the first option to try to avoid such problems to repeat, would be to inhibit water from becoming ice, a result that could be obtained by using additives. Another option, could be to implement a different fuel tank, even if it is an expensive and long term measure. In the meanwhile, using FSII (Fuel System Icing Inhibitor) or make operational change could reduce the risk of ice restricting fuel flow like happened to the BA038 flight. Obviously, changing for example the cruising altitude to prevent temperature from dropping too low (with the always growing cost of fuel) is not an option. Although the investigation is still in progress, to reduce the risk of fuel icing the AAIB released safety recommendations “to introduce interim measures for the Boeing 777, powered by Trent 800 engines, to reduce the risk of ice formed from water in aviation turbine fuel causing a restriction in the fuel feed system”, “to consider the implications of the findings of the investigation on other certificated airframe / engine combinations” and “to review the current certification requirements to ensure that aircraft and engine fuel systems are tolerant to the potential build-up and sudden release of ice in the fuel system.
