This is the fourth update from AirSafe.com on the ongoing investigation into the accident at London's Heathrow Airport involving a British Airways 777. This update is based on information released by the AAIB the week of 11 May 2008.
This article is based on the AirSafe.com podcast published on 20 May 2008. The podcast, available at http:/podcast.airsafe.org, presents the highlights of the most recent update from the Air Accidents Investigation Branch concerning the status of the investigation. There is a brief review of the details of the accident, followed by a discussion of the new information provided by the AAIB report, and an analysis of the progress of the investigation.
The accident aircraft was a scheduled international flight from Beijing, China to London, England, and the flight was routine until about two miles from touchdown. The engines would not respond to commands to increase thrust, and as a result the aircraft touched down about 1000 feet short of the runway. There was a significant fuel leak, but no post-crash fire. All 136 passengers and 16 crew members were able to successfully evacuate the aircraft, and the most serious injury was a broken leg suffered by one passenger.
The three previous AAIB updates in January and February 2008 provided detailed information about the flight, including the state of the fuel and fuel systems, and the condition of the engines and their associated control systems. You'll find details about the previous updates, as well as links to previous podcasts describing the accident sequence, at http://777.airsafe.org.
For the last several months, the AAIB has focused on the fuel and fuel systems of the aircraft. Extensive examination of the aircraft and detailed analysis of information from the flight data recorder and other onboard recording systems have revealed no evidence of an aircraft or engine control system malfunction.
The fuel was extensively tested, and showed no evidence of contamination or excessive water content. Although the aircraft had experienced very cold temperatures, the fuel temperature remained well above freezing. Detailed examination of the fuel system revealed a loose connection in one of the fuel lines as well as the presence of small pieces of debris, but these conditions led to no unusual deterioration or physical blockages.
The ongoing investigation has also found no evidence that a wake vortex encounter, bird strike, engine icing, or electromagnetic interference played a role in the accident. The focus of the investigation continues to be the fuel system and the engines, with the goal of understanding why neither engine responded to demands for increased power even though all of the engine control functions operated normally.
Under the direction of the AAIB, the engine manufacturer Rolls-Royce and the aircraft manufacturer Boeing are conducting further tests on the engines and fuel system with the goal of replicating the fuel system performance seen in the accident flight. Additional work is being conducted to gain a more complete understanding of the dynamics of the fuel as it flows from the tank to the engine.
No individual parameter associated with the accident flight was outside of previous operating experience. However, the AAIB is using a data analysis team to review data from a large sample of flights on similar aircraft to see if there was a combination of parameters that was outside of previous experience.
Unlike the last AAIB interim report issued in February 2008, this report did not contain any recommended operational changes for the 777.
I'd like to take a moment to share my opinion about the progress of this investigation. This crash investigation has not yet come up with an explanation for what happened. This is in spite of having a largely intact aircraft, a large volume of data from the accident aircraft and comparison data from similar flights, and the combined resources the engine manufacturer, the aircraft manufacturer, and the British government. This probably means that if the AAIB does come up with an explanation for why the accident happened, the explanation will include a combination of circumstances that had not been previously anticipated by aircraft designers or aircraft operators.
The suggestions made in previous AirSafe.com podcasts about how to evaluate what's being published about this investigation are still valid .
If you're interested in following the investigation online or in the news media, keep in mind that prior to the completion of the investigation by the AAIB, anyone outside of the investigation, including aviation safety experts and the largest news media organizations, will have access only to a fraction of the relevant information.
The AAIB will likely provide several more updates prior to publishing a final report, and these updates represent the most authoritative sources of information about the ongoing investigation.
Podcast Audio and Video
Audio: MP3 | Video: iPod/MP4 | WMV | Google Video | YouTube
Podcast Transcript
http://www.airsafe.com/podcasts/show48.htm
Additional Accident Details and Related Podcasts
http://777.airsafe.org
21 May 2008
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I'm reminded of the US Air 737 that suffered a fatal crash several years ago upon approach to Pittsburgh. As I recall, it took investigators quite some time to determine that a hydraulic actuator locked the rudder to maximum position, which caused the aircraft to crash. As I remember, it took a bit of doing to replicate the condition and, even so, some doubt may have remained as to the exact cause.
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