What happened
On 2 February 2001, a Boeing 757-200, registration SE-DUP, was operating a charter flight from Stockholm/Arlanda to Malaga, Spain. While cruising at flight level 310 over Jönköping, Sweden, the flight crew experienced a sudden disturbance in the aircraft's pitch. Simultaneously, cabin crew in the aft galley witnessed a loud bang and a flash of light emanating from the control panel for the ovens and water boilers.
Shortly after the flash, smoke began to emerge from the area around the control panel. A cabin attendant used a fire extinguisher to treat the panel, which helped the smoke to dissipate. Due to the uncertainty regarding potential damage to the aircraft, the commander declared an emergency and requested a diversion to Göteborg/Landvetral airport. The aircraft landed safely on runway 03, though one cabin attendant required medical attention for smoke inhalation.
The investigation
Technical investigators examined the compartment behind the galley control panel and discovered extensive soot on both the exterior of the panel and within the internal compartment. The investigation focused on the electrical cannon plug that connects the control panel to the galley's ovens and water boilers. This component was found to be severely burnt, with deformed insulation and evidence of extreme heat that had melted the copper in the electrical cables.
Metallurgical analysis of the connector pins revealed no manufacturing defects or contamination. Instead, the evidence suggested that heat generation had occurred internally within the pin couplings over an extended period. The investigation also noted that the electrical system serving the galley equipment was underdimensioned, meaning the design did not allow for sufficient heat dissipation when all galley appliances were operating at full power.
Findings
- The incident was triggered by an electrical flash-over within the electrical system supplying the aft galley ovens and water boilers.
- The electrical system was underdimensioned for the load of the galley equipment, leading to overheating.
- The heat generation within the connector pins caused the insulation to degrade, eventually leading to the short circuit.
- The manufacturer has since implemented an obligatory modification to the system to prevent recurrence.