Heat damaged wiring loom involving Boeing 737-476F, Brisbane Airport, Queensland, on 6 September 2018

What happened

On 6 September 2018, a Boeing 737-476 freighter was in the hanger at Brisbane Airport, Queensland undergoing routine maintenance. The crew reported that the cockpit voice recorder (CVR) was not testing and the circuit breaker was tripping.

While engineers were conducting troubleshooting on the aircraft, they discovered a heat damaged wiring loom located in the aft^[1] lower cargo hold ceiling, adjacent to the CVR mount rack. The wires were severely burnt in a localised area with melted insulation and evidence of a possible fire. Engineers suspect this may have been caused by swarf^[2] damaging the wiring and causing it to arc. Swarf ingress in the wiring loom was discovered from previous cargo conversion work.

Figure 1: Heat damaged wiring loom

Source: Operator’s engineering department

Safety message

This incident highlights the importance of ensuring that while an aircraft is in maintenance, that all aircraft components are checked thoroughly to ensure proper functionality. When conducting any work on an aircraft, it is also vital to ensure that all areas are thoroughly cleaned to ensure no debris is left behind, as it may cause faults to the aircraft and its systems.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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1. Aft - situated in or near the rear of the aircraft
2. Swarf - chips of metal, wood or plastic.