NTSB marks 10th anniversary of crash of TWA 800

Citation

(2006), "NTSB marks 10th anniversary of crash of TWA 800", Aircraft Engineering and Aerospace Technology, Vol. 78 No. 6. https://doi.org/10.1108/aeat.2006.12778fab.018

NTSB marks 10th anniversary of crash of TWA 800

NTSB marks 10th anniversary of crash of TWA 800

Keywords: Air safety, Major accidents

With the 10th anniversary of the crash of TWA Flight 800, the National Transportation Safety Board released a fact sheet that reviews lessons learned from the accident investigation and the progress toward ensuring that similar tragedies do not happen in the future.

The Board's review found that significant safety improvements have been implemented over the past ten years, but that more needs to be done to avoid another accident like TWA 800.

TWA 800, a Boeing 747, crashed on July 17, 1996, minutes after takeoff from John F. Kennedy International Airport on a flight to Paris, France. All 230 persons aboard the aeroplane died in the accident. The Safety Board conducted an exhaustive four-year investigation and determined that the accident was caused by an explosion in the center wing fuel tank, resulting from ignition of the flammable fuel/air mixture in the tank.

“The crash of TWA 800 was a watershed event for the air carrier industry,” said NTSB Acting Chairman Mark V. Rosenker. “In the intervening years, a lot of thought and effort has been devoted to the issues raised by this accident, and the public is safer for it.”

The most prominent issues raised by the TWA 800 accident concern protection against flammable fuel tank vapours and ageing electrical systems.

Rosenker noted that fleet-wide inspections and analytical reviews of fuel tank design have resulted in significant measures that have the potential to reduce the likelihood of an ignition event inside a tank, and that fuel pumps, fuel quantity indicating systems, in-tank wiring, co-routed wiring, and operational procedures have been modified to make fuel systems safer.

“Equally important,” Rosenker said, “is the prospect of substantially reducing fuel tank flammability exposure – something that was seen as impractical ten years ago but is now feasible, even in this difficult era when airline operators need to be extremely conscious of costs.”

But while applauding the FAA and industry for the progress that has been made, Rosenker cautioned that the process is moving much too slowly. “Ten years after the TWA accident, fuel tank inerting systems are not in place on our airliners, and flammability exposure is largely unchanged, and proposed rule changes do not include the majority of fuel tanks which are in the wings of transport aeroplanes, nor this country's large fleet of cargo aircraft.”

Consequently, he added, reduction in fuel tank flammability remains on the NTSB's most wanted list of safety improvements.

Rosenker also expressed disappointment that the FAA did not act on the NTSB's immediate, interim recommendations, issued a few months after the TWA accident, that were aimed at reducing the fuel tank flammability problem until longer-term solutions are in place. The recommendation was closed by the Safety Board last year and given an “unacceptable action” status.

Rosenker noted that the TWA accident gave great impetus to legislation that revolutionised the ability of the families of the victims to obtain accurate and timely information about an airliner accident and the subsequent investigation. Passed in 1996, Public Law 104-264 assigned to the NTSB the role of integrating the resources of the Federal government with those of local and state authorities, and the airlines, to meet the needs of aviation disaster victims and their families. Today, the emergency planning accomplished by the airlines, in co-operation with the NTSB, serves as a model for the transportation industry in this country and throughout the world.

Further information on the investigation of the crash of TWA 800, the text of the final report and the recommendations stemming from the accident are available on the NTSB web site at: www.ntsb.gov

TWA 800 fact sheet

The crash of a Boeing 747, operating as TWA flight 800, on July 17, 1996, tragically took the lives of all 230 persons aboard, and resulted in one of the most extensive, expensive and technically difficult investigations in the Safety Board's history.

After a four-year investigation, the Safety Board determined that the probable cause of the crash was an explosion in the center wing fuel tank; the ignition of the flammable fuel/air mixture in the tank was attributed to an electrical failure.

The accident investigation highlighted two significant issues with major implications for the design and operation of transport aeroplanes. One concerns the potential vulnerability of fuel tanks, the other the problems raised by ageing aircraft wiring.

Fuel tank vulnerability

Since, the TWA 800 accident, there have been two additional airliner fuel tank explosions. On March 3, 2001, a center wing tank explosion destroyed a Thai Airways B-737 at the terminal in Bangkok, Thailand.

Currently under investigation is a left wing fuel tank explosion on a Transmile Airlines B-727 in Bangalore, India on May 4, 2006. At the time of the explosion the aeroplane was waiting to be towed and only the auxiliary power unit was running. The exact source of the ignition energy for the fuel/vapour mixture has not been determined, but initial examination of the structural damage to the left wing indicates that most likely the wing would have failed had the aeroplane been in flight at the time of the explosion. Such a structural failure in flight would not be survivable.

The TWA 800 investigation found that factors contributing to the accident were:

A flawed design and airworthiness certification philosophy that fuel tank explosions could be prevented solely by eliminating all likely ignition sources.

The certification of the Boeing 747 design that had heat sources located beneath the center wing tank with no means to reduce the heat transferred into the fuel tank, and no protection against the flammability of vapours that accumulated in the tank.

The Safety Board concluded that dealing just with ignition sources was not sufficient to ensure safe flight and that fuel tank flammability must be addressed.

On December 13, 1996, the NTSB issued two safety recommendations aimed at reducing flammable fuel/air mixtures on airliners. One suggested short-term measures in aeroplane operations that could immediately reduce the levels of these flammable mixtures (A-96-175), while the other called for design changes that would necessarily take years to implement (A- 96-174).

Both recommendations were placed on the Board's most wanted list of safety improvements.

The Safety Board is disappointed that the FAA has refused to require air carriers to adopt short-term actions that could be quickly implemented to lessen fuel tank vulnerability. In November 2005, the NTSB classified this recommendation “Closed- Unacceptable Action.”

The FAA has made significant progress in eliminating potential ignition sources in the entire fleet of transport aeroplanes. In May 2001, the FAA issued Special Federal Aviation Regulation Number 88 (SFAR 88) requiring a comprehensive analysis of all potential ignition sources in aircraft fuel tanks, and provisions to remove the ignition source risk.

The FAA also is in the process of issuing over a hundred airworthiness directives that address specific problems that were found in various aeroplane models.

On November 22, 2005, the FAA issued a Notice of Proposed Rulemaking (NPRM) titled “Reduction of Fuel Tank Flammability in Transport Category Aeroplanes” which proposes new rules that should greatly reduce the chances of a catastrophic fuel-tank explosion by requiring a flammability reduction system be installed and used in transport category aeroplanes.

The NTSB strongly supports adoption of this NPRM for both existing and new aeroplanes, and has urged the fastest possible implementation.

The NPRM, however, will not apply this requirement to airliner wing fuel tanks, nor to cargo aircraft. The Safety Board believes this system should be required for cargo as well as passenger aircraft, and that wing fuel tanks should also be covered. As the recent Bangalore incident illustrates, the potential for ignition of fuel/air vapours can exist in wing tanks as well as center wing tanks.

The Safety Board is concerned that movement on the NPRM has been so slow and that closure of the comment period has been repeatedly postponed, finally closing on May 8, 2006. Airliner fuel tanks are as flammable today as they were ten years ago.

Ageing wiring

In the TWA 800 investigation, the Safety Board found evidence to conclude that the most likely source of ignition energy for the fuel tank explosion was a short circuit that introduced electrical energy into the tank.

Examination of numerous other transport aeroplanes revealed wide- spread problems related to the ageing of wiring and other aeroplane systems that could result in catastrophic accidents.

On April 7, 1998, the Safety Board issued a series of recommendations (A- 98-34 to 39) addressing wiring problems that potentially could result in fires or provide fuel tank ignition sources.

Additional recommendations (A-00-105 to 108) concerning the ageing and maintenance of systems installed in the entire fleet of transport aeroplanes were issued following the Safety Board's public meeting (August 22-23, 2000) at which the TWA 800 final investigation report was considered.

On October 5, 2005, the FAA published an NPRM titled “Enhanced Airworthiness Program for Aeroplane Systems/Fuel Tank Safety” that proposed a combination of actions to ensure the safety of commercial aeroplanes by improving the design, installation, and maintenance of electrical wiring interconnection systems.

The Safety Board believes this NPRM has many positive aspects and introduces numerous potential improvements, and looks forward to its implementation.

However, the Safety Board also has noted that the NPRM is incomplete in that it does not require improved training of maintenance personnel to ensure adequate recognition and repair of potentially unsafe wiring conditions, better documentation and reporting of potentially unsafe electrical wiring conditions, and the incorporation of new technology, such as wide-spread use of arc-fault circuit breakers and automated wire test equipment.

Victim and family assistance

Following the crash of TWA 800, difficulties experienced by family members, similar to those experienced following previous major accidents, further underscored the need for a single agency to facilitate assistance efforts.

The US Congress passed the Aviation Disaster Family Assistance Act of 1996. (Public Law 104-264) which requires the Safety Board to provide assistance to the victims and family members following major airline accidents.

In response, the NTSB created the Office of Family Affairs, now the Office of Transportation Disaster Assistance. This office, currently with a staff of five, is charged with co-ordinating the resources of the federal government at an accident scene, facilitating a co- operative working relationship between federal, state and local responders, and co-ordinating with the air carriers to insure assistance is provided to victims and their family members.

A380 vortices

The A380 may leave significant vortices in its wake. Aircraft flying behind are advised to maintain a sufficient separation margin to ensure safety.

Pending ongoing research, the ICAO recently stipulated a 16km separation margin for the A380. The international study that is currently underway is assessing the exact magnitude of the A380 wake turbulence.