Regulatory Report

Rule Aims to Eliminate Explosions

The FAA has proposed a sweeping set of new regulations in 14CFR Parts 25, 91, 121, 125, and 129 to help eliminate the possibility of fuel-tank explosions by reducing flammability of large aircraft fuel tanks. The proposed rules are published in Notice No. 05-14, dated November 23, 2005.

After seven years of research, the FAA has concluded that unless the aviation industry tackles this problem, "nine more transport category airplanes will likely be destroyed by a fuel-tank explosion in the next 50 years." Since 1960, 17 airplanes were destroyed by fuel-tank explosions, four of which killed passengers. "Although we cannot forecast precisely when these accidents would occur," the FAA notice stated, "computer modeling indicates these events are virtually certain to occur."

The key to preventing such explosions, according to the FAA, is both to prevent ignition and even if ignition occurs, make it difficult for fuel tank ullage (vapor space inside tanks) to explode. The FAA has issued many airworthiness directives and Special FAR 88 to try to eliminate ignition sources inside fuel tanks, but this will never be 100-percent effective. The FAA believes that reducing the oxygen concentration in ullage below a level that will support combustion will help prevent fuel-tank explosions.

While the FAA has focused much attention on the possible use of nitrogen-inerting systems to reduce the oxygen concentration, this notice of proposed rulemaking (NPRM) departs from that effort. The NPRM would set performance-based requirements for acceptable levels of flammability exposure in tanks that are prone to explosion or mandate the installation of some method of mitigating ignition inside the affected fuel tanks. An inerting system could use nitrogen to reduce oxygen levels in ullage, but as long as the oxygen level is below the allowable limit, that will meet the requirements of the new rule.

The NPRM would mandate development of these systems for all type certificate holders for "many large turbine-powered transport category airplanes with high-risk fuel tanks." Operational regulations in Part 91, 121, 125, and 129 would be changed so that operators would have to maintain such systems.

The FAA estimates that this rule could affect up to 3,800 Airbus and Boeing airplanes in the U.S. A simplified inerting system would weigh 100 to 250 pounds and cost $140,000 to $225,000 per airplane. This NPRM would not apply to cargo-only airplanes.

Comments on this NPRM are due by March 23, 2006. To view the full NPRM, click here and click on the "Recently Published Rulemaking Documents" link and then on the November 23, 2005 link to "Reduction of Fuel Tank Flammability in Transport Category Airplanes."