Ageing Aircraft - Electrical Wiring


Deterioration in an aircraft electrical wiring interconnection system (EWIS) is often difficult to identify and repair. The EWIS on many older aircraft still in service was often designed on the ‘fit and forget’ principle, but both age itself and inadvertent collateral damage during unrelated maintenance or routine inspections cause airworthiness problems. Both deterioration and damage are often associated with the difficult-to-detect condition of wiring within the bundles of wires routed together as in ‘looms’. These looms and aircraft wiring generally are often in locations which are difficult to access and, even where they are accessible, only the condition of the outer wires can be properly checked. A lot of effort has therefore been put into developing more effective inspection processes for wiring loom integrity in particular, but also into practical methods of confirming wiring circuit integrity generally. Attention has also been focused on good maintenance practice in respect of wiring looms which have in the past often been vulnerable to undetected damage inadvertently caused during base maintenance.

TWA 800

A widely known example of an accident in which the probable initiating factor was arcing due to damaged insulation on electrical wiring occurred in 1996, when a 23-year-old Boeing 747-100 on an international revenue passenger flight exploded in mid-air shortly after take off from New York. See: B741, en-route, East Moriches NY USA, 1996


Improved inspection and diagnostic processes for EWIS in aging aircraft are being progressively mandated but the prospect of longer term progress lies in new technology. Live-wire testing of aircraft EWIS during flight is now possible and can detect intermittent faults that cannot be located during maintenance on the ground. Arc Fault Circuit Interrupter technology is being developed to provide additional safety measures when a fault occurs. Moving forward, nanoscale sensors embedded within emerging ‘smart’ wire systems will detect and correct faults in real time. In the longer run, fibre optics and wireless technologies will reduce the need for bulky wiring looms. While these and other techniques are being developed and tested, fleets must rely on diligent application of the array of currently available diagnostic technologies.

In some instances, where wiring deterioration has been found in locations where the consequences could be instantly disastrous, such as in the FQIS systems inside fuel tanks, means of protecting against the consequences of ignition, such as nitrogen inerting, have been examined, although not yet implemented.

Safety Reporting

Finally, as with Ageing Aircraft - Structural Failure, it also appears that there has often been ineffective safety reporting to the NAA. That authority, based on consideration of individual reports, has potentially approved an aircraft operator or maintenance organisation to take corrective actions to seemingly minor but possibly significant incident or inspection findings which, when considered together, could have helped identify interventions capable of preventing a significant Incident or Accident.

Accidents and Incidents

The following events involved an airworthiness factor associated with Electrical Power:

Related Articles

Further Reading

  • In 2004, the UK Air Accidents Investigation Branch (AAIB) published its findings on three serious incidents involving electrical wiring damage and took the exceptional opportunity to review all three incidents together in the context of industry developments and make generic rather than the conventional incident-specific safety recommendations. The two areas addressed were wiring damage and circuit breaker design. See AAIB Bulletin: Incidents resulting from damaged electrical wiring
  • The FAA Aircraft Certification Service on-line training course "Lessons Learned From Transport Airplane Accidents"

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