Show #40: Third Update of the AAIB
Investigation of the Crash of
a British Airways 777
Title: Crash of British Airways 777 at Heathrow on 17 January 2008 - Update 3
Date: 20 February 2008; Length: 8:47
This is the third 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 on 18 February 2008, and focuses on analyses of the fuel system, the engines, and their associated control systems. You can listen to or watch the podcast at the following links:
Audio: MP3 | Video: iPod/MP4 | WMV | YouTube
Accident investigation details
Other Conversation at AirSafe.com podcasts
0:54: 777 crash details
1:20: Additional Details from the latest AAIB update/p>
1:53: Final moments of the flight
2:49: Analysis of Fuel Temperature
3:30: Fuel System Anomalies
4:07: Analysis of the Engine
4:29: Landing gear damage
5:02: Recommended procedure changes for 777 operators
6:18: Speculation about the causes of the accident
7:29: Suggestions for evaluating unoffical accident analysis
8:14: Additional resources from AirSafe.com
Hello, and welcome to the Conversation at AirSafe.com. I'm your host Dr. Todd Curtis, the creator of AirSafe.com, your reliable source of airline safety and security information since 1996.
This is show #40 - Crash of British Airways 777 at Heathrow on 17 January 2008 - Update 3.
This show was first broadcast on February 20, 2008.
In this Conversation, I'll review the most recent update from the Air Accidents Investigation Branch concerning the status of the investigation.
The investigation is ongoing, but substantial amounts of information from the aircraft has been analyzed, allowing the AAIB to focus their efforts to find the cause or causes of the accident.
In this show, I'll briefly discuss the accident, and will discuss in greater detail the information provided by the AAIB report released on the 18th of February 2008.
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.
This latest AAIB update provided additional insights into the final moments before touchdown, the state of the fuel and fuel systems, and the condition of the engines and their associated control systems.
The damage caused by the landing gear had a direct role in the post crash fuel spill, and the report also showed how aircraft evacuation procedures contributed to the amount of fuel that spilled. Previous AAIB reports indicated that the engines did not respond to either autothrottle or autopilot commands shortly before landing. The latest report is a refinement of what was stated before.
The first officer took control for the landing at a height of approximately 780 feet, and shortly afterwards the autothrottles commanded an increase in thrust from both engines. The engines initially responded, but at a height of about 720 feet the thrust of the right engine reduced.
About seven seconds later, the thrust reduced on the left engine to a similar level. The engines did not shut down and both engines continued to produce thrust at an engine speed above flight idle, but at less than the commanded thrust.
The engines failed to respond to further demands for increased thrust from the autothrottles, or from the manual inputs of the flight crew. The airspeed reduced as the autopilot attempted to maintain its intended glide slope angle, and by the time the aircraft had descended to about 200 feet above the ground, the airspeed had reduced to about 108 knots. The autopilot disconnected at about 175 feet, and afterwards the aircraft descended rapidly, contacting the ground just inside the airfield boundary fence and about 1,000 feet short of the runway.
During the flight, the aircraft traveled through high altitude regions of unusually low temperatures, with the crew changing altitudes at one point to fly through warmer air.
British weather authorities noted that although the temperature was unusually low, it was not exceptionally low.
During the flight, the fuel temperature dropped to as low as minus 34 degrees Celsius. However, an analysis of fuel samples taken after the accident showed that the freezing point of the fuel was much lower, at minus 57 degrees Celsius.
The fuel was tested by more than one laboratory, and initial results found that the fuel showed no signs of contamination or unusual levels of water.
This report made no mention of ice or slush forming in the fuel or fuel system during any portion of the flight.
Examination of the fuel tank revealed a loose connection in one of the fuel lines. Small pieces of debris were recovered in both the left and right main tank, and in two fuel pumps. Debris was also found in the left engine fuel oil heat exchanger (FOHE).
Detailed examination of both the left and right engine high pressure fuel pumps revealed signs of damage that could indicate that there was either a restriction in the fuel supply to the pumps or that there was an excessive aeration of the fuel. In spite of the damage, both pumps were found to be still being capable of delivering full fuel flow.
This update did not conclude what role, if any, that these fuel system anomalies played in the accident. An examination of the engines indicated no evidence of a mechanical defect. Also, there was no indication of ingestion of either birds or ice.
An examination of the data from the electronic engine controllers (EEC) and the quick access recorder (QAR) revealed no anomalies in the engine control system.
The electronic engine controllers and fuel metering valves were found to have responded correctly following the reduction in engine thrust.
During the impact and subsequent ground roll, the nose gear collapsed, the right main landing gear separated from the aircraft, and the left main landing gear was pushed up through the wing.
The right main landing gear ruptured the rear right wall of the center fuel tank and penetrated the cargo hold. The two front wheels of the right main landing gear broke away and struck the rear right fuselage, penetrating the cabin adjacent to rows 29 and 30.
Damage from the collapse of the left main landing gear left the crew unable to close the left spar valve, while damage from the right main gear limited the crew's ability to close the right spar valve. Because of the way the evacuation procedure was executed, the crew could not close the right spar valve, and this contributed to the size of the fuel spill.
The evacuation checklist developed by Boeing for the 777 called for moving the fuel control switches to the cut-off position prior to operating the fire handles. This sequence would have allowed the crew of the accident aircraft to close the right spar valve in spite of the damage to the part of the electrical system that controlled that valve.
According the the AAIB report, a revised checklist from British Airways, for which Boeing had raised no technical objection, split the responsibility for moving the fuel control switches and operating the fire handles between the two flight crew members, and did not have any measure in place to ensure the correct sequence of actions.
During this accident, the fire control handle for the right engine was operated before the fuel control switch for that engine was moved to the cut-off position, keeping the spar valve in the open position and allowing fuel to escape.
AAIB noted that this situation was not causal to the accident but, could have had serious consequences in the event of a fire during the evacuation.
The AAIB recommended that Boeing notify all triple seven operators of the need to operate the fuel control switch to cut-off prior to operation of the fire handle, for both the fire drill and the evacuation drill, and to ensure that all versions of its checklists are consistent with this procedure.
I'd like to talk a bit about how the latest report addresses some of the more widely discussed possible causes of the accident.
There has been plenty of speculation about the causes of the accident by persons and organizations not connected to the accident investigation. One of the more prominent set of speculations was an article in the February 12, 2008 issue of the Wall Street Journal Online, which mentioned a buildup of ice crystals or slush in the fuel system as a possible cause of the engine thrust anomalies.
Nothing in the recent AAIB report directly supports that portion of the Wall Street Journal Online's article. In fact, the AAIB has not found evidence of any significant water contamination, and also found that the the fuel stayed well above its freezing point throughout the flight.
The Wall Street Journal Online article also expressed doubts that there would be any safety recommendations released with the next update to the investigation. In fact, the report, which was released six days after the article was published, did have the safety recommendation concerning the emergency checklists.
These significant differences between the speculation of the Wall Street Journal Online and the update from the AAIB illustrate the difficulty that any outsider has when it comes to drawing conclusions about an investigation that is still in progress.
The suggestions made in previous AirSafe.com podcasts about how to evaluate what's being published about this investigation are still valid and are worth repeating.
If you're interested in following what is said about the investigation online or in the news media, keep this in mind: prior to the completion of the investigation by the AAIB, those 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.
Finally, take the time to read between the lines and to figure out what is fact and what is speculation. For additional information and other resources related to this investigation, please visit 777.airsafe.org.
There you will find a synopsis of the findings of the accident investigation, links to previous podcasts about this accident, and links to other resources related to airline safety and security.
You will also find links to contact information for AirSafe.com.
Thanks for listening, and I'll see you next time.
Dr. Todd Curtis is the author of the book Parenting and the Internet (Speedbrake Publishing, 2007) and is also the host of the podcast of the same name.
http://www.airsafe.com/podcasts/show40.htm -- Revised: 20 February 2008