Over the years there have been a number of in-flight smoke and fire events where contaminants ignited by electrical faults allowed the fire to be sustained and spread. The FAA and the National Transportation Safety Board (NTSB) have conducted aircraft inspections and found wiring contaminated with items such as dust, dirt, metal shavings, lavatory wastewater, coffee, soft drinks, and napkins. Sometimes wire bundles and surrounding areas have been found to be completely covered with dust.
In recent years both the FAA & Industry have realized that current maintenance practices may not be enough to address aging non-structural systems. Over time, insulation can crack or breach, thus exposing the conductor.
While age is not the sole cause of wire degradation, the likelihood of EWIS damage from inadequate maintenance, contamination, improper repair, or mechanical damage increases over time.
Examples of bad practice include piercing (needling) wires to test continuity or voltage, or using a metal wire or rod as a guide to feed new wires. These practices could cause a breach in the wiring insulation that can contribute to arcing.
Research has demonstrated that wiring can be harmed by collateral damage when maintenance is being performed on other aircraft systems. For example, a person performing an inspection of an electrical power center or avionics compartment may inadvertently cause damage to wiring in an adjacent area. Aviation Accident Investigators have specifically cited the need for improved training of personnel to ensure adequate recognition and repair of potentially unsafe wiring conditions.
TWA 800 accident 1996 – Fuel Tank Explosion believed caused by a wiring fault.
Following investigations into the TWA 800 Fuel Tank Ignition and Flammability Reduction initiative* (SFAR-88), this initiative ran alongside the ATSRAC investigation process.
* Complementary - but separate initiatives, Note however ATSRAC tasking included understanding of wiring-induced failures that may also be potential ignition sources in fuel tank system installations.
ATSRAC spent two years investigating core issues which were issued as reports and a further two years moving the reports into rulemaking and developing AC’s Advisory Circulars.
ATSRAC was established to coordinate aging systems initiatives with the FAA. This process also incorporated the Air Transport Association’s (ATA) aging system task force (ASTF) activities into ATSRAC. ATSRAC observes evidence of aging effects in airplane wiring installations accumulating in aircraft going back to the 1960s.
Recommendations include requirements to change SWPM information, Inspection Criteria, and Training and include a new term EWIS.
EWIS Initial and Recurrent training courses are available either classroom-based with Sofema Aviation Services or as an online training.
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