Saturday, July 1, 2006
The Inerting Controversy
Regarding fuel tank safety, the comments seem to be roughly divided into two camps: (1) those who do not have to consider cost generally favor the inclusion of a flammability reduction system, or inerting, (2) and those faced with the installation through retrofit and the maintenance costs are in opposition to inerting.
The dozens of comments amounting to a few hundred pages stem from a Federal Aviation Administration (FAA) Notice of Proposed Rulemaking (NPRM) published November 23, 2005, which put forth the idea of installing an inerting system in all transport category airplanes of more than 30 seats (see AM, May, p. 10). The program is to exempt cargo planes, but require retrofit in all others and installation in new-production aircraft. The proposal stems from the center wing fuel tank (CWT) explosion in 1996 of TWA Flight 800, a Boeing 747, and the explosions of tanks in two 737s as well. The May 4 left wing tank explosion in Bangalore, India, of a Transmile Airlines 727 during a ground repositioning, lends a certain timeliness to the NPRM.
If the FAA persists in its proposal to retrofit aircraft, the task would involve thousands of aircraft and would impact maintenance and support activities for years to come.
Not unexpectedly, Airbus sees the problem as having little to do with their designs. Even with air conditioning packs located below the CWT, the Airbus design does not use the CWT as a heat sink, which is endemic to the Boeing design. But from Boeing's point of view, they do not want to be uniquely saddled with a weight penalty and system complexity.
The FAA stance is that inerting is needed in addition to ignition prevention in order to stave off future TWA 800 style events. The European counter-claim is that the risk of future fuel tank explosions has been exaggerated by a factor of five and the cost/benefit ratio by a factor of 28. The new A380 will not feature a CWT, and Airbus asserts that inerting is not necessary because the new airplane will be fully compliant with ignition prevention measures. The new Boeing 787 will feature inerting for all tanks, in part because the composite wings will require additional protection against lightning strikes.
Operators are adamantly opposed to retrofitting inerting systems.
At this point, from the comments submitted to the FAA, it seems fair to say that if the FAA were to "go it alone," there would be two distinct levels of safety among the world's airlines. Harmonization, or the achievement of a common standard, would not be possible.
To be sure, electrical safety in fuel tanks has been enhanced through the Special Federal Aviation Regulation (SFAR) 88 initiative, by which airworthiness directives have been published for Boeing, Airbus, and other manufacturers, aircraft.
It is unlikely that consensus will be reached on the issue of fuel tank inerting. Fuel tank explosions are the unlikely outcome of heated fuel giving rise to explosive vapors. Electrical safety has been enhanced, but cannot give positive assurance. Removal of all ignition sources cannot but only be aspired to. The most assured method of precluding explosions is to inert all fuel tanks. Because of the cost associated with inerting just the heated CWTs, the fix was going to be strung out to a 2014 implementation - if the FAA decides to persist.
Later this year, the U.S. Air Force will test in two engines of an eight-engine B-52 a coal based fuel, with the expressed intent of running all military jets on this blend as soon as it's proven. If and when this new fuel technology migrates across to the civilian sector, the fuel flammability figures used to calculate tank explosivity should change dramatically. The whole ball game is being changed by different imperatives. The FAA has yet to issue a final rule on fuel tank inerting. Given the controversy kicked up by the comments, the economic hardships of the industry, and the changing fuel situation generally, the FAA may well stall for time.
Herewith, extracts of some of the comments to the FAA's inerting proposal:
The National Transportation Safety Board:
"The Board is aware of the first ARAC's finding that fuel tanks located in the wings cool more quickly than some airplanes' center wing fuel tanks, which can be heated by proximity to warmer areas in the airplanes and that, consequently, fuel tanks located in the wings have a significantly lower average flammability exposure or ignition risk. However, the fact remains that wing fuel tanks have exploded, and Safety Recommendation A-96-174 was not limited to certain types of fuel tanks, or to tanks with specific types of exposure, or to tanks with explosive risks that vary or lessen over time. ...
"Finally, the Safety Board notes that additional benefits from onboard flammability reduction systems can be realized, but that the FAA does not address any of these. Nitrogen-producing equipment can be used to provide fire protection for avionics, electrical compartments, unoccupied spaces, and cargo compartments. For example, on February 8, 2006, a DC-8 cargo airplane was on fire when it landed at Philadelphia, Pennsylvania, International Airport. The fire was quickly spreading in the cargo area, and the crew may have had only a few [minutes to spare] in which to land the airplane. An inerting system may have suppressed or extinguished the fire, significantly improving the safety of the flight. Further, the introduction of nitrogen-producing technology can eliminate the need for Halon-based fire suppression systems and potable water compressors, reducing maintenance costs and weight."
The Families of TWA Flight 800 Association:
"Finally, nine years after the explosion of TWA Flight 800 the FAA has proposed a preventive, constructive action to eradicate the possibility of a center wing fuel tank explosion. This action required time, work, and expense, which we believe was necessary yet could have happened more quickly. This brings us to the next step in the fuel tank inerting process. The projected certification and implementation to complete the NPRM is 2014, which is entirely too long. This costly action we believe is well spent. Can the airline industry and FAA afford another mass loss of life similar to the TWA 800 incident?"
The Independent Pilots Association (the union of United Parcel Service pilots)
"The [NTSB] comments on our recent DC-8 cargo fire accident ... and how inerting systems might have prevented or substantially reduced the magnitude of the fire. The recent accident involving an Air Force C-5A Galaxy aircraft at Dover Air Force Base ... involved the catastrophic hull loss of a large cargo transport aircraft with (estimated) 300,000 pounds of fuel on board with no fire. This aircraft was equipped with a nitrogen based inerting system. While the investigation is far from complete, the 17 people on board this aircraft (some soaked with fuel after the accident) may owe their lives to the fact that a Fuel Tank Inerting System was installed aboard this aircraft."
"Historically, increased levels of nitrogen in confined areas has resulted in injury to personnel during aircraft maintenance. BA does not support installation of such a system."
Association of European Airlines:
"Human error creates continuing risk. Each attempt to fix an electrical system presents the possibility of an inadvertent introduction of a new ignition source. Maintenance oversights, such as the failure to properly install electrical bonds or improper installation or overhaul of components, compound the possibility of an ignition source developing."