Just less than 10 years ago, the tragic in-flight break up of TWA "Flight 800" set in motion the action for many amendments to regulations affecting aging aircraft, particularly fuel tanks. As a result of the Flight 800 investigation and two other fuel-system related incidents, the NTSB identified fuel tank safety as one of its top three priorities. These priorities trickle down to impact not only aircraft design and products, but also aircraft maintenance. In this article, we will look at the use of transient suppression devices (TSDs) to comply with some of the new fuel tank safety regulations and assess some of new regulations from the maintenance perspective.
In September of 2000, the NTSB issued fuel tank safety recommendations aimed at increasing protection against fuel tank flammability. The FAA initially responded to the NTSB recommendations with airworthiness directives related to fuel quantity indicating systems on the Boeing 747 and 737 classic airplanes. Thereafter, the FAA issued Special Federal Aviation Regulation No. 88 (SFAR 88 -- Apr. 19, 2001 and as amended Sept. 10, 2002) that set higher safety standards for Part 25 aircraft. These actions were aimed at eliminating sources of ignition in and near the fuel tank.
Besides setting new certification requirements for airframe manufacturers, SFAR 88 requires STC holders to perform system safety assessments if their modification in any way impacts the fuel system or comes near the critical fuel areas with electrical energy. The result of the safety assessment is an action item list. The action items result as potential discrepancies are found. The objective is to bring the fuel system and wiring near fuel areas to a higher level of safety. SFAR 88 has now been incorporated into the FAR as Amendment 102.
Safety inspection and review
From a maintenance perspective, the new fuel tank regulations require operators to inspect airplanes and review maintenance procedures and inspection instructions for deficiencies with regard to fuel tank safety. A considerable part of this effort should have been previously accomplished by the airframe manufacturer and supplied through service information to the operator. However, the manufacturer's review generally does not include the aftermarket modifications that many operators have installed. The operator's safety review includes an evaluation of configuration management of the airframes (noting any modification that may provide a source of ignition in the fuel tank area -- i.e., the impact of high voltage in-flight entertainment system wiring, new strobe lighting, fuel pump wiring, etc.) and establishing inspection procedures to verify that the safety of the installed equipment and wiring does not compromise fuel system safety. The regulations set Dec. 6, 2004 as the deadline for implementing new maintenance and inspection programs.
However, on July 30, 2004, the FAA extended the compliance deadline for operators until Dec. 6, 2008 to comply with the new maintenance procedures. The extension was to provide consistency with the FAA requirements under the "Aging Airplane Safety Rule" of Dec. 6, 2002 (requiring inspections and airframe reviews of aircraft in service for 14 years or more).
So where are we?
The NTSB concluded that flammable vapors in the center fuel tank under the passenger deck exploded, tearing Flight 800 apart.
No Fire in the Hole - Revisited New regulations affecting aircraft fuel tanks By Fred Workley July 2001 Editor’s note: Workley’s original "No Fire in the Hole" article...