The BA plane that crashed at Heathrow in January was probably brought down by ice in its fuel system, according to an accident report
by the Air Accident Investigation Branch. The Boeing 777 managed to land so that the 136 passengers and 16 crew escaped without serious injury but the AAIB believes the flow of fuel dropped causing the engines to lose power less than a minute before touchdown.
The report concluded thus:
“The investigation has shown that the fuel flow to both engines was restricted; most probably due to ice within the fuel feed system. The ice is likely to have formed from water that occurred naturally in the fuel whilst the aircraft operated for a long period, with low fuel flows, in an unusually cold environment; although, G-YMMM was operated within the certified operational envelope at all times.
“All aviation fuel contains water which cannot be completely removed, either by sumping or other means. Therefore, if the fuel temperature drops below the freezing point of the water, it will form ice. The majority of flights have bulk fuel temperatures below the freezingpoint of water and so there will always be a certain amount of ice in the fuel.
2To prevent the ice causing a restriction requires either: the fuel system must be designed in such a way that the ice in the fuel does not pose a risk of causing an interruption of the fuel supply to the engine or; prevention of the water from becoming ice in the first instance. Changes to the fuel system design could make the system more tolerant, but would take time to implement and would certainly not be available within the near term. Therefore, to reduce the risk of recurrence interim measures need to be adopted until such design changes to the fuel system are available.
“One option would be to prevent the water from becoming ice, such as through the use of FSII. Alternatively, operational changes to reduce the risk of ice formation causing a restricted fuel flow at critical stages of flight could be introduced. Such changes could be implemented quickly, but must not compromise the safe operation of the aircraft.
“Although the exact mechanism in which the ice has caused the restriction is still unknown, in detail, it has been proven that ice could cause a restriction in the fuel feed system. The risk of recurrence needs to be addressed in the short term whilst the investigation continues.”
The investigation will continue and a number of recommendations have been made to the Federal Aviation Administration and the European Aviation Safety Agency for further review.