No Fire in the Hole - Revisited
New regulations affecting aircraft fuel tanks
By Fred Workley
Editor’s note: Workley’s original "No Fire in the Hole" article discussed currently installed technologies used for fire prevention, fire suppression, and monitoring in cargo compartments and it appeared in AMT Feb. 2000. The article is also available in the Article Search link at www.amtonline.com.
On May 7, 2001, the Federal Aviation Administration issued Special Federal Aviation Regulation (SFAR) No. 88 to minimize the potential for failures that could cause ignition sources in fuel tanks on new and existing airplanes. The new rules require airplane operators and manufacturers to change how airplane fuel tanks are designed, maintained and operated. For the first time, there are mandated requirements to minimize flammability in new airplanes.
The Trans World Airlines (TWA) 800 accident in July 1996 was the start of an extensive review by the FAA and industry that has focused on three areas of concern:
1. Preventing ignition from any source within the fuel tank
2. Fuel flammability
3. Fuel tank inerting
Fuel tank inerting recommendations are expected to be available from the FAA in July 2001.
SFAR 88 is applicable to 6,971 turbine-powered, transport category airplanes that are manufactured by Airbus, Aerospatiale (ATR), Boeing, British Aerospace, Bombardier, DeHavilland, Dornier, Embraer, Fokker, Lockheed, Saab and Shorts that have 30 or more seats. The new rule does two things. First, for existing airplanes, it requires manufacturers to conduct a one-time design review of the fuel tank system for each transport airplane model in the current fleet to ensure that failures could not create ignition sources within the fuel tank. Also, manufacturers must design specific programs for the maintenance and inspection of fuel tanks to ensure the continued safety of the systems. There are also operational changes for existing airplanes, like not running the fuel boost pumps on the B-737 when a tank is empty.
Minimizing ignition sources
Aircraft manufacturers will be required to further minimize the possibility of ignition sources in the fuel tanks on new aircraft designs. This means that transport category airplanes developed in the future will have to address potential failures in the fuel tank system that could result in possible ignition sources. Furthermore, fuel tank safety must be developed and supported by the manufacturer for the operators’ maintenance and inspection programs that identify safety-critical maintenance actions. Manufacturers will need to reduce the time fuel tanks operate with flammable vapors in the tank by designing fuel tank systems that consider adjacent heat sources. This can be done by one of two ways:
1. Minimizing the development of flammable vapors
2. Developing another means, such as onboard fuel tank inerting to prevent catastrophic damage in the unlikely event that ignition might occur
The effective date of the rule is June 6, 2001. Manufacturers have 18 months to conduct the safety review and to develop maintenance and inspection programs as required by the SFAR. Likewise, operators have 36 months from the effective date to incorporate an FAA-approved maintenance and inspection program into their operating procedures. To date, the FAA has issued or proposed about 40 airworthiness directives (ADs) on fuel tank safety. Many of these ADs are a result of lessons learned from the TWA 800 accident investigation and subsequent analysis. Adverse service experience has also shown that if specific maintenance procedures are not carried out on certain airplane fuel systems, there may be a degradation of the design features intended to preclude ignition of vapors within the tank (i.e. bonding, grounding and shielding). This means that technicians will be performing mandatory fuel system maintenance required by the limitations section of the Instructions for Continued Airworthiness for each airplane model. Additional ADs are an expected result of feedback received from the design review of existing aircraft that is required by the new SFAR.