Icy fuel caused Boeing 777 crash landing

Official investigation prompts safety changes

A crash landing at Heathrow airport in January last year was most likely caused by ice forming within the fuel system, a report from the Air Accidents Investigation Branch (AAIB) has concluded. 

The ice build-up caused severe power reduction in both engines as the Boeing 777 approached the runway, resulting in a sudden loss of airspeed. The passenger flight from Beijing, China, only just managed to clear perimeter roads and buildings, before touching down 330m short of the runway. All 152 people on board survived the crash landing.

The British Airways captain Peter Burkill was praised in the report for altering the flap settings in the final moments of the aircraft’s descent, thus reducing drag and delaying impact for 50 metres. This was enough to ensure that the aircraft landed on a grass apron within the airport.

The AAIB report said that as the aircraft approached Heathrow at 720 feet, the right engine of the aircraft ceased responding to autothrottle commands for increased power. Instead the power reduced to 1.03 engine pressure ratio (EPR). Seven seconds later the left engine power reduced to 1.02 EPR. The investigation identified that the reduction in thrust was due to restricted fuel flow to both engines.

Since the incident last year, Boeing and engine-maker Rolls-Royce have introduced measures to prevent ice forming in the aircraft’s fuel.

The US Federal Aviation Administration and the European Aviation Safety Agency have also been asked to carryout a study into expanding the use of anti ice additives in aviation turbine fuel on civil aircraft.

The AAIB has now made a further nine recommendations mainly relating to crashworthiness issues.

The report identified several factors that led to the fuel flow becoming restricted: 

• Accreted ice from within the fuel system was released, causing a restriction to the engine fuel flow at the face of the Fuel Oil Heat Exchanger (FOHE), on both of the engines
  
• Ice had formed from water that occurred naturally in the fuel whilst the aircraft operated with low fuel flows over a long period. The localised fuel temperatures were in an area described as the ‘sticky range’ meaning that ice crystals were most likely to stick to their surroundings. 
  
• The FOHE, although compliant with the applicable certification requirements, was shown to be susceptible to restriction when presented with soft ice in a high concentration, with a fuel temperature that is below -10°C and a fuel flow above flight idle.
• Certification requirements, with which the aircraft and engine fuel systems had to comply, did not take account of this phenomenon as the risk was unrecognised at that time.