A Special Bulletin has been issued by the Air Accidents Investigation Branch (AAIB) of the U.K. Department for Transport regarding its investigation of the crash landing of a British Airways B777 at London's Heathrow Airport last month. The bulletin updates and adds to information released previously by the AAIB. The bulletin stops short of stating any conclusions about the cause of the accident, but it does imply that a partial interruption of fuel flow is the current focus of the investigation.The latest report, AAIB Bulletin S1/2008 Special, is a 6-page 'pdf' document. Here are some highlights of information presented in the bulletin.
Weather: Temperature conditions during the flight were described in the report as "unusually cold," but remained above the freezing point for the fuel samples taken from the aircraft.
Recorded Data: The AAIB successfully retrieved data from the Digital Flight Data Recorder (DFDR), the Cockpit Voice Recorder (CVR), and the Quick Access Recorder (QAR) from the accident aircraft. The Bulletin states:
The recorded data indicates that there were no anomalies in the major aircraft systems. The autopilot and the autothrottle systems behaved correctly and the engine control systems were providing the correct commands prior to, during, and after, the reduction in thrust.Engineering Examination: There were no indications of any pre-existing problems with any of the aircraft systems.
- Examination of the engines indicated no evidence of a mechanical defect or ingestion of birds or ice.
- Examination of the high pressure fuel pumps for both engines "revealed signs of abnormal cavitation on the pressure-side bearings and the outlet ports" suggesting "either a restriction in the fuel supply to the pumps or excessive aeration of the fuel," however both pumps were assessed as being still able to deliver full fuel flow.
- Fuel samples taken from the aircraft conformed with Jet A-1 specifications and "there were no signs of contamination or unusual levels of water content."
- "Small items of debris" were found in the right-main fuel tank, the left-main tank water scavenger inlet, the right-center tank override pump, and the left center tank water scavenge jet pump. The AAIB states that "the relevance of this debris is still being considered."
Investigations are now underway in an attempt to replicate the damage seen to the engine high pressure fuel pumps, and to match this to the data recorded on the accident flight. In addition, comprehensive examination and analysis is to be conducted on the entire aircraft and engine fuel system; including the modelling of fuel flows taking account of the environmental and aerodynamic effects.Here are the links to the three reports relating to this accident investigation that have been issued to date by the AAIB:
- AAIB Ref: EW/C2008/01/01 (Initial report)
- Initial Report Update - 23 January 2008
- AAIB Special Bulletin: 1/2008 - February, 2008
