What happened
On March 6, 2003, a Boeing 747-230B cargo aircraft operated by a German airline departed Sharjah, United Arab Emirates, bound for Frankfurt, Germany. Shortly after reaching a cruising altitude of FL310, the aircraft experienced a series of significant electrical failures. The autopilot, autothrottle, and galley power supply disconnected simultaneously, and the number 2 altimeter entered standby mode. Several circuit breakers also tripped, affecting flap control systems and leading-edge flap drives.
The crew reported a faint smell of burning cables in the cockpit and a stronger electrical burning odor in the main deck galley. Although the crew inspected the adjacent cargo area and found no visible smoke or flames, they decided to continue the flight as planned, monitoring the galley area every 15 minutes. During the approach to Frankfurt, the crew found that leading-edge slats 1 and 3 could not be deployed, and the inboard flap indication remained incorrect. Consequently, the aircraft performed a landing at a speed increased by 25 knots.
The investigation
The BFU investigation focused on the electrical malfunctions and the source of the burning odor. Upon inspection of the aircraft after cargo unloading in Frankfurt, investigators discovered partially burned insulation mats in the area between the lower cargo hold and the main deck. A hole approximately 5 cm by 10 cm was found in the aluminum structure of a Dado-Vent-Box at station 780.
Investigators found significant fire damage to two wiring harnesses and the thermal insulation in this area. The investigation revealed that the galley power supply cable had been improperly secured to a flap control wiring harness using a plastic cable tie, which deviated from standard design practices. The investigation also noted that the Dado-Vent-Box in question extended further outward than its original design, creating a contact point with the underlying wiring.