'Special Conditions' for Fuel Tank Safety Challenged

Air Safety Week, Feb 9, 2004

A proposal to grant "special conditions" for a Boeing [NYSE: BA] system to prevent fuel tank explosions has drawn sharp rebukes for the appearance of favoritism and skirting the established certification process.

In response to a Boeing proposal to equip its aircraft with a lightweight system to inert center wing tanks, the Federal Aviation Administration (FAA) outlined in a Dec. 9, 2003, notice the criteria under which it would consider such a system for approval (see ASW, Dec. 15, 2003).

"Special conditions" can be issued by the FAA in those cases where existing regulations do not provide adequate safety standards for "novel or unusual" design features. The FAA believes Boeing's flammability reduction system (FRS), for which it is seeking certification, is one of those situations.

The FAA sought public comments on the matter, which were due Jan. 23. However, according to an FAA official, comments will be accepted through February 20. This extension will allow time for coordination and input from Europe's Joint Aviation Authorities (JAA) and from the National Transportation Safety Board (NTSB). The elimination of explosive vapors in fuel tanks is on the NTSB's "Most Wanted" list of aviation safety improvements. Given the concern over fuel tank safety since the 1996 explosion that destroyed TWA Flight 800, the NTSB's position on the FAA's proposed "special conditions" is especially important. And of course the criteria need to be harmonized, hence the importance of incorporating JAA views into the final deliberations.

Already, the Association of European Airlines (AEA) charged that the FAA's gambit smacks of favoritism.

"It looks like the docket is written in such a way that it fits Boeing preliminary design features. This should not be the case, because regulation guidance should be unprejudiced and available before development of any design," the AEA's Jan. 23 letter declared.

Among the most substantive inputs to the docket was an anonymous 10-page analysis, obtained separately by this publication. This submission reflects a detailed appreciation of the issues, the certification process, and the operational and safety considerations. It is also consistent with themes and concerns expressed by other commentators. The docket manager, who was aware of this unsigned input, said it has been included in the docket.

This anonymous analysis argues that approval of the proposed inerting system based on statistical analysis is "not in the public interest." Herewith, the salient arguments:

A. Adequacy of existing regulations

Item (as contained in Dec. 9, 2003, notice of proposed special conditions).

The applicable airworthiness regulations do not contain adequate or appropriate safety standards for the design and installation of this system, e.g., the flammability reduction system (FRS) as propounded by Boeing, design and functioning of which has been outlined in this publication (see ASW, Dec. 23, 2002,; March 31, 2003; Dec. 22, 2003).

Comment (as contained in anonymous analysis; the author prefers not to reveal his identity).

[Federal Aviation Regulation] FAR 26.981(c) clearly states the system requirement. FAR 25.1301 defines what is required in terms of function and installation. FAR 25.1309 identifies the requirements applicable to equipment, systems and installation. Additional requirements are applicable based on system type. For example, FAR 25.1438 is applicable if the system contains components that operate at high pressure. FAR 25.1461 if it contains high energy rotors. FAR 25.831(b) if it can contribute hazardous gases or vapors to occupied compartments. FAR 25.1322 for warning, caution and advisory lights. FAR 25.1357 for circuit protection devices, etc.

We fail to comprehend what is missing.

Item. These proposed special conditions contain additional safety standards that the [FAA] administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

Comment. We believe special conditions are not needed. There is nothing unusual or special about the [proposed] system. It consists of components presently used in aircraft, except for the air separation module (ASM). The ASM is no different than a filter; it filters out oxygen. The three basic requirements that apply to the system are FAR 25.981, FAR 25.1301, and FAR 25.1309. The ASM is a pressurized component and FAR 25.1438 would apply to it. The performance of the ASM requires no regulation as an applicant can trade NEA quality (nitrogen concentration) for flow rate.

Item. Advisory circulars AC 25.981-1B, "Fuel Tank Ignition Source Prevention Guidelines," and AC 25.981-2, "Fuel Tank Flammability Minimization," describe ... an acceptable means ... for demonstrating compliance with the regulations.

Comment. AC 25981-2 states that an oxygen concentration of 10 percent or less by volume is acceptable [the special condition proposed by the FAA allows 12 percent]. (See ASW, Dec. 15, 2003) Minimum performance inherent in the AC must be preserved. Public interest requires it. Granting special conditions would, in our opinion, represent a lack of confidence in the FTHWG [Fuel Tank Harmonization Working Group].