Federal safety officials on Friday urgently asked the Federal Aviation Administration to protect fuel tanks in the nation’s airliners from heat sources that could touch off the kind of explosion that brought down TWA Flight 800.
The damage on airplane parts recovered from the ocean floor and carefully reconstructed “are consistent with an explosion originating within the tank,” the National Transportation Safety Board said in a letter to the FAA.
Investigators have been unable to figure out what sparked the catastrophic explosion inside the tank, but leading theories include static electricity, faulty wiring or a spark from the center tank’s fuel pump.
Despite the fact that no conclusions have been reached in the July 17 explosion that killed 230 people, “NTSB investigators believe there are potential safety improvements that can be made,” the letter said.
The NTSB urgently recommended that the FAA require tanks to be designed so that they will not contain any explosive fuel air mixtures, and to consider adding insulation between the fuel tanks and heat-generating equipment such as air conditioners.
It also said operational procedures should be modified to reduce the possibility of an explosion - for example, turning the air conditioners off while planes wait for takeoff, filling center tanks with cooler fuel from underground tanks, and keeping enough fuel in the tanks to prevent volatile vapors from accumulating. Also, it said the FAA should require probes in the tanks.
The NTSB noted that the military prevents the risk of fuel tank ignition by inserting nitrogen into the tanks to create “an oxygen-deficient fuel-air mixture that will not ignite.”
However, the NTSB said it recognizes that developing and installing the nitrogen systems on commercial airliners would be “expensive and may be impractical.”
The FAA and Boeing Co. said it would carefully review the recommendations, which apply to all aircraft with similar fuel tank configurations.
“FAA takes the board’s recommendations very seriously, and it will respond to today’s proposals in a timely fashion,” the agency said, noting that it has “responded positively” to 90 percent of the NTSB’s urgent recommendations.
In a statement from its headquarters in Seattle, Boeing said its “position where safety is concerned is to err on the side of caution. We will take action and support any directives from the FAA.”
“Some of the NTSB recommendations may involve issues with far-reaching effects for the entire aviation industry,” Boeing added. “It is imperative that each recommendation be thoroughly reviewed, analyzed and evaluated by all interested parties before any changes are implemented so we ensure that appropriate safety measures are initiated.”
NTSB spokesman Peter Goelz said “We are not even close to issuing a probable cause” of the crash.
An accident investigator, who spoke on condition of anonymity, said static electricity that could result as fuel is transferred through the plane’s pipelines is one possible catalyst being seriously considered now.
The investigator called static electricity the ignition “source de jour.”
“It is a complex issue, one that is extremely difficult to investigate and even more difficult to prove,” the source said. “A couple of weeks ago it was wire bundles, whether they were wrapped or not. Then we found out they were wrapped and that theory was eliminated.”
The probe into the deadly explosion has already changed air travel. Because of the possibility of a criminal act, airports imposed new security measures during the summer. Now possible mechanical causes are leading to new safety recommendations.
Word of the warning came as the FAA announced plans in Washington Friday to require inspections of fuel pump wiring systems in some 747 planes.
The agency said the proposed directive “is not the result of any finding” from the probe into the TWA disaster, but instead is “an example of the FAA’s continuous efforts to ensure aircraft are operated in an airworthy condition.”
Flight 800 exploded shortly after takeoff from Kennedy Airport to Paris, breaking apart into fiery pieces that rained over miles of ocean.
Five months after the tragedy, scallop boats continue to rake up the last pieces of the plane, and investigators stick to three possible causes: a bomb, a missile, or a mechanical malfunction.
xxxx SAFER FUEL TANKS Recommendations from the National Transportation Safety Board to improve the operation of Boeing 747s and other commercial airliners with similarly designed fuel systems: Install probes in fuel tanks and add cockpit fuel tank temperature displays to help determine fuel tank temperatures; Install additional insulation between fuel tanks and heat sources, such as air conditioning packs and hot air ducts; Refuel the center fuel tanks from cooler ground fuel tanks or carry additional fuel to prevent volatile vapors from forming; Limit the use of heat sources while planes are on the ground, such as the air conditioners immediately below the center fuel tanks; Improve management of fuel distribution among various tanks to keep temperatures in safe operating ranges and establish minimum fuel quantity standards for center fuel tanks. Consider the development of a nitrogen-enriched fuel tank that would eliminate flammability by replacing oxygen. Nitrogen is already used in military aircraft, but the NTSB concedes that installation on commercial airliners is expensive and may be impractical. Revise in-flight handbooks that may understate the extent to which air conditioners can elevate the temperature of fuel inside the tanks. -Associated Press