Preventive maintenance practices and detailed inspections may be the most effective method to reducing ignition sources around fuel systems. The FAA recently highlighted the need for improved maintenance practices when performing modifications or maintenance. The regulations now require the following notice provision in manuals:
It is imperative to prevent or significantly reduce potential contamination or debris from coming into contact with the wiring and components during all maintenance, repairs, and modifications. This begins with always being aware of potential wiring contamination, and remembering to install appropriate protection (e.g. plastic sheeting), as necessary, to cover avionics/electrical wiring and components. Furthermore, a "clean-as-you-go" attitude helps maintain the integrity of the installation. In other words, care should be taken to protect wire bundles and connectors during work, and to ensure that all shavings, debris, and contamination are cleaned up after work is completed.
While this may be common sense, my colleagues and I can provide you with many stories that have been reported of items and equipment being left on, inside, and around the airplane.
When performing maintenance on airplanes with TSDs installed, the typical avionics rules apply. Most importantly, be careful to protect the connector pins. If the pins get bent or do not make contact, the equipment that the TSD is protecting may not operate properly. While the equipment may not work quite right, the nice feature about the TSD is that it always works. As a passive, fail-safe device, the TSD will always protect the wiring and the fuel tank. The failure mode is an open circuit. Therefore, the protection is always effective.
Finally, anytime there is an inspection, check the wiring harnesses and connectors around the fuel tank for broken wires or compromised wiring insulation. Look for leaking or seeping fuel. Connector seals can often be a source for fuel leaks. Maintenance is the first line of preventive measures -- how often have you ever seen a captain or first officer look into the wheel well at a fuel tank wall?
We expect that the aging aircraft rules will someday require added protection to aircraft wiring. The common circuit breaker is no longer as trustworthy as we might expect. While maintenance practices will supplement the enhanced safety level brought on with new airframe devices, maintenance will be the key element to keeping these airplanes safe, particularly the classic fleet.
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...