Incident Overview
On August 15, 2003, at approximately 16:00 UTC, a SAAB 2000 aircraft registered as HB-IZJ operated by Swiss International Air Lines as flight SWR 1042 encountered a serious incident. The aircraft had departed Zurich Airport at 15:48 UTC en route to Cologne, Germany. During cruise at flight level 220, the copilot detected an unusual odor reminiscent of melting plastic. The flight crew initially suspected the air conditioning system and shut down pack 1. When the odor persisted, they also deactivated the windshield heating and checked various panels for heat. Unable to identify the source, the crew decided to return to Zurich and requested priority landing. The aircraft landed uneventfully at 16:33 UTC. All 50 passengers and 4 crew members remained uninjured.
Flight History
Prior to the incident, on August 7, 2003, another crew on the same aircraft had reported a similar electrical burning smell and found that circuit breaker E 28 had tripped, interrupting power to some cabin lights. Maintenance replaced a damaged lamp holder and a suspected faulty ballast. On August 12, the circuit breaker tripped again. Maintenance attempted to reset it between flights but it repeatedly tripped, so the breaker was secured in the open position and troubleshooting deferred. The aircraft continued in service.
Investigation Findings
Examination revealed that an electrical arc had occurred in flight between two live cables and the aircraft structure. The root cause was the routing of the cables, which allowed their insulation to become damaged, leading to the arc. The serious incident was attributed solely to this technical fault. No human factors or organizational issues were identified as contributing factors.
Probable Cause
The serious incident was caused by an electrical arc that occurred in flight between two live cables and the aircraft structure, because the routing of the cables allowed damage to their insulation.