Fixing the Problem That May Have Caused the British Airways 777 Crash

Recent findings from the AAIB accident investigation point to ice buildup in the fuel system as the key factor in the January 2008 crash of a British Airways 777 in London. On March 11th, 2009, the NTSB called for a redesign of the fuel system, and for the affected aircraft to have those changes installed within six months after the redesign is complete.

You can hear this information in the podcast here or at at podcast.AirSafe.org

In the January 2008 crash, the flight from Beijing to London was routine until the the aircraft was on final approach, when both engines had an uncommanded power reduction, or engine rollback, which caused the plane to land short of the runway. Although the aircraft was seriously damaged, only one of the 136 passengers was seriously injured, and there were no serious injuries among the 16 crew members.

The Air Accidents Investigation Branch in the UK headed the investigation, with the help of several other organizations, including the aircraft manufacturer Boeing, the engine manufacturer Rolls Royce, and British Airways.

The series of updates and interim reports from the AAIB, the most recent of which was released in early March 2009, revealed that the likely cause of the dual engine rollback was ice blockage in a critical fuel system component that led to a reduction of fuel flow to the engine.

These findings didn't come easily. The AAIB focused its efforts on the fuel system because of the unusual conditions of the accident flight. That flight was exposed to rather cold atmospheric conditions, so cold that the crew changed altitudes at one point to fly through warmer air.

The AAIB reviewed the minimum fuel temperature data from over 141,000 777 flights. About 13,000 of these flights were on aircraft operating with the Rolls Royce Trent 800 series engine, the same kind as on the accident aircraft. Of those 13,000 flights, only 118 had fuel temperatures at takeoff that were at or below the takeoff fuel temperature of the accident flight, and during the approach phase, only 70 had fuel temperatures that were as low or lower than the fuel temperature on the accident flight.

The two most likely accident scenarios that were investigated by the AAIB both involved ice formation within the fuel system, leading to a reduction of fuel flow. This ice formation was possible because the aircraft fuel did contain some water. This kind of contamination is normal, and in fact the fuel from the accident aircraft was tested, and found to be in compliance with the appropriate fuel specifications.

After an extensive analysis of the fuel system, the AAIB concluded that the most likely scenario for the engine rollback was that ice formed in the fuel pipes within the main fuel tank, and that during the latter part of the approach phase of the flight, factors such as turbulence, aircraft pitch changes, and increasing temperatures could have contributed to the sudden release of accumulated ice into the fuel feed system of both engines. This ice would have restricted the fuel flow through a component called the fuel oil heat exchanger and would have led to the engine rollbacks.



The AAIB recommended that Boeing and Rolls Royce review the aircraft and engine fuel system design, and make changes that would prevent ice from restricting fuel flow through the fuel oil heat exchanger.

In the US, the National Transportation Safety Board went further, recommending that within six months of completing the redesign, that it be incorporated in all 777 aircraft using the Trent 800 engines. Some of the airlines that fly Trent 800 equipped triple sevens include Air New Zealand, American Airlines, British Airways, Cathay Pacific, Delta Airlines, El Al, Emirates, Kenya Airways, Malaysia Airlines, Singapore Airlines, and Thai Airways. There are about 220 such aircraft currently in service.

The NTSB's recommendations were influenced by a second 777 rollback event. On November 26, 2008, a Delta 777, powered by two Trent 800 series engines, experienced a single-engine rollback while in cruise on a flight from Shanghai to Atlanta. The crew was able to address the issue and continued the flight without incident. Later analysis indicated that there was a blockage of the fuel oil heat exchanger on that engine that was likely due to ice accumulation. Although the engine rollbacks on the British Airways accident aircraft and the Delta Airlines incident aircraft occurred during different phases of flight, the fuel temperatures at the time of the rollbacks were about equal.



Taken together, these developments are good news for the aviation community, especially passengers and crews flying on 777s equipped with Trent 800 engines. The investigative authorities have determined the likely cause of the event, the changes to the fuel system that are needed are well understood, and the engine and aircraft manufacturers are well on their way to developing solutions that will prevent similar occurrences in the future.

For more on this investigation, or for information about aviation safety or aviation security issues, please visit 777.AirSafe.org.

Do Plane Crashes Happen in Threes? - Sometimes, Yes

Note: updated version of article published 24 July 2014

Since AirSafe.com was launched in 1996, the site has tracked fatal events and other significant events involving airline passengers. When these events occur, especially if two occur a just a few days apart, I sometimes get the "Do bad things like plane crashes always happen in threes?" question asked by visitors to the site, by members of the media, and by others. I used to just dismiss the question out of hand because events like plane crashes, especially those involving passenger airliners, are very rare, and the circumstances are usually very different for each crash, often involving different airlines, different aircraft types, and even different countries.

Although it's easy to reject the original question, it is quite legitimate to ask a related question about how frequently groups of rare events occur over a relatively short period of time. One day, just for fun, I turned the "things happening in threes" question into something that could be analyzed systematically using the information within AirSafe.com. I changed the general question into the following specific question: "How frequent are sequences of three or more fatal or significant aviation safety and security events where the time between events is ten days or less?"

For the purposes of answering this question, I limited the data to those events that are regularly tracked by AirSafe.com. These would be plane crashes or other airline events that kill at least one passenger, or other events that AirSafe.com considers to be significant with respect to aviation safety or aviation security (see http://www.airsafe.com/events/method.htm for a detailed definition of a fatal or significant event). Multiple events due to the same cause (for example, the four crashes associated with 9/11) were treated as one event.

Significant events that don't kill anyone sometimes attract more media attention than the average plane crash. The January 2008 ditching of a US Airways A320 in the Hudson River in New York was one example. It was very dramatic, it got a huge amount of media exposure, and no one was killed.

A review of the AirSafe.com records from 1996, the year AirSafe.com was launched, to February 2009 revealed some interesting facts:

* With the exception of 2007 and 2009, every year since 1996 included at least one sequence of three fatal or significant events that were separated by no more than ten days In fact, there was a sequence of five significant (but nonfatal) events in January 2008.

* There were seventeen sequences of three or more events that were separated no more than ten days. Three were sequences of five events, three sequences had four events, and the other eleven consisted of three events each. Correction: Since this article was published, a previously overlooked fatal accident from 24 August 1999 was added, and this led to an additional sequence of three for that year.

* Most of the fatal and significant events tracked from 1996 to the present were not part of any sequence of three or more events.

* Well known fatal events that were a part of one of these sequences include the Swissair MD-11 crash in 1998, the Concorde crash in 2000, the August 2006 crash of a Comair jet, in Lexington, KY, and the August 2008 crash of a Spanair MD83 in Madrid.

* Well known events that were not a part of one of these sequences include the ValuJet and TWA Flight 800 crashes in 1996, the Alaska Airlines crash in 2000, and the four crashes associated with 9/11.

* There have been five fatal or significant events in a 70-day period between 20 December 2008 and 25 February 2009, but only two of them have been less than ten days apart.

For twelve of the past 13 calendar years (1996 to 2008), there has been at least one grouping of three or more fatal or significant events that occurred over a relatively short period. At the same time, no information has come about in the investigations of any of those events that indicates that there was any sort of connection among them, or any evidence that the earlier events in the sequence made a later event more likely.

After reviewing the facts, I no longer say that plane crashes don't happen in threes. Since at least 1996, they have happened in threes, in fours, and in fives. Let us all hope that there are no sixes and sevens in our future.

Review AirSafe.com Events by Year
1996, 1997, 1998, 1999, 2000, 2001, 2002
2003, 2004, 2005, 2006, 2007, 2008

Turkish Airlines Plane Crash in Amsterdam

25 February 2009; Turkish Airlines 737-800; Amsterdam, Netherlands: The aircraft, on a scheduled international flight from Istanbul, Turkey, to Amsterdam, Netherlands crashed in a field about a mile (1.6 km) short of the runway. The fuselage was broken into three major sections, and both engines were torn off. There was apparently no post crash fire. Three crew members, including both pilots, were killed, as were at least six others among the 135 passengers and crew members.

AirSafe.com's Initial Report on this Accident
Audio: MP3 | Video: iPod/MP4 | WMV | Google Video | YouTube

Additional information about this event.

For more videos, visit the AirSafe.com YouTube channel.

Updates to Two Most Recent Continental Crashes

AirSafe.com just finished updating the status of the 20 December 2008 crash of a Continental Airlines 737-500 at Denver. The aircraft, which was on a scheduled flight to Houston's Intercontinental Airport, departed the runway during takeoff and skidded across a taxiway and a service road before coming to rest in a ravine several hundred yards from the runway. The aircraft sustained significant damage, including a post crash fire, separation of one engine and separated and collapsed landing gear. There were about 38 injuries among the 110 passengers and five crew members, including two passengers who were seriously injured. Because this did not involve the death of an airline passenger, this is a significant event as defined by AirSafe.com

Below are the audio and video versions of the podcast.

Continental Airlines Accident in Denver
Audio: MP3 | Video: iPod/MP4 | WMV | Google Video | YouTube

For more videos, visit the AirSafe.com YouTube channel at video.airsafe.org.

Additional Information on the Buffalo Accident
The site added a page with fatal and significant events involving the Dash 8 model airliner, the same model involved in the fatal 12 February 2009 crash in Buffalo, NY.

Additional information about both the Buffalo and Denver events is available at http://www.airsafe.com/events/airlines/cal.htm

Continental Connection Crash in Buffalo 12 February 2009

The aircraft, a scheduled flight from Newark, NJ and operated by Colgan Air, crashed in a residential area about five miles from the airport. At least one house on the ground was destroyed. All 44 passengers and four crew members were killed, along with one person on the ground.

AirSafe.com's Initial Report on this Accident
Audio: MP3 | Video: iPod/MP4 | WMV | Google Video | YouTube

Additional information about this event.
Plane crashes involving the Dash 8
Synopsis of NTSB accident investigation

For more videos, visit the AirSafe.com YouTube channel.

Interview with Bird Strike Expert Dr. Ron Merritt

On January 18th, 2009, three days after the bird strike related ditching of US Airways Flight 1549 in New York, Dr. Todd Curtis of AirSafe.com interviewed bird strike expert Dr. Ron Merritt. He's currently the president of Detect, Inc., which manufactures bird strike avoidance radars. Dr. Merritt was also at one time the military commander of US Air Force unit responsible for understanding and reducing bird strike hazards to Air Force aircraft. During this wide ranging conversation, they discus a variety of bird strike and wildlife hazard topics, including the need for wildlife experts in the US Airways accident investigation team, wildlife control policy issues, and the history of the key bird strike organizations in the US and Canada.

Interview with Dr. Merritt and Dr. Curtis

Post about the related interview of Dr. Curtis on the Escapes radio program.

For more information on the accident, including videos and background information on bird strike hazards and airliner ditchings, visit:
hudson.airsafe.org

Interview on the Escapes Radio Talk Show

On February 9th, 2009, Dr. Todd Curtis of AirSafe.com was interviewed on the "Escapes" radio show hosted by Ann Lombardi of the the Trip Chicks, who along Wendy Swartzell run the Atlanta area travel company Passport to Adventure. During the show, we discussed several of the issues around the previous month's ditching accident involving a US Airways A320 in New York, including what can be done about bird strike hazards, and how passengers should deal with fear of flying.

Listen to the interview

For more information on the accident, including videos and background information on bird strike hazards and airliner ditchings, visit:
hudson.airsafe.org