Incident Overview
On 6 March 2003, a Boeing 747-230B cargo aircraft operated by a German airline experienced a serious incident shortly after departure from Sharjah, United Arab Emirates, en route to Frankfurt Main. The aircraft, originally built in 1985 and converted to a freighter in 1992, had three crew members on board: a captain, a first officer, and a flight engineer. No injuries occurred, and the aircraft sustained light damage.
Flight Events
After reaching cruising altitude at Flight Level 310, the crew observed several automatic system disengagements: Autopilot B, autothrottle, and galley power supply. The number 2 altimeter entered standby mode. Multiple circuit breakers popped, including those for galley power control, trailing edge flap asymmetry & fail, alternate leading edge flap drive (Nos. 1–4), alternate inboard trailing edge flap drive, and inboard flap control position. The crew was able to reset the autopilot, autothrottle, and altimeter, but did not reset the circuit breakers.
A faint smell of burnt insulation was detected in the cockpit. The flight engineer noticed a stronger electrical burning smell in the main deck galley, but inspection through a window into the cargo compartment revealed no signs of fire or smoke. The crew decided to continue the flight, monitoring the galley area approximately every 15 minutes.
During approach to Frankfurt Main, the Nos. 1 and 3 leading edge slats could not be extended. The inboard trailing edge flap indication remained in the "up" position even though the flaps were extended. The approach was flown at an increased speed (25 knots above normal), and the aircraft landed safely at 16:19 local time.
Investigation Findings
Post-flight inspection revealed burned insulation mats in the lower cargo area around the oxygen bottles. A 5 cm × 10 cm burn hole was found in the aluminum structure of a Dado-Vent-Box at station (STA) 780. Two cable bundles behind the box—the main galley power supply (115 V, 3-phase, up to 150 kVA) and another bundle of over 80 wires for various systems (flaps, slats, ice protection, cargo handling)—showed severe fire damage. Soot and heat marks were present on the pressure vessel structure.
The Dado-Vent-Box at STA 780 had been removed and reinstalled during a D-check (heavy maintenance) in 2002. The bolt of that box had chafed through the insulation of the galley power cable, causing a short circuit and fire. The fire spread via the circulation of conditioned air through the box. Further investigation showed that the galley power cable had been bundled together with the flap control cable bundle using a plastic cable tie, contrary to the manufacturer's standard design practices.
Chafing marks were also found on other Dado-Vent-Boxes in contact with cable bundles. The aircraft manufacturer noted that the affected box extended "several inches" further outward than originally delivered, likely due to the 1992 conversion.
Probable Cause
The investigation concluded that the cable fire was most likely caused by the chafing of a bolt of the Dado-Vent-Box (STA 780) against the electrical supply cable bundle of the upper galley. The fire spread to adjacent cable bundles, resulting in the observed system failures. The improper bundling of the galley power cable with other wiring during the 2002 D-check was considered a contributing factor, though the source attributes the root cause to the chafing.
Aftermath
The operator immediately inspected its two other B747-200SF aircraft, verifying clearances between all Dado-Vent-Boxes and cable bundles, and added extra insulation. The conversion company, Bedek Aviation Group, issued preventive measures on 2 April 2003, including relocating cable bundles, adding chafe protection, and trimming the Dado-Vent-Boxes where they contacted cables.