Australian investigators say the in-flight loss of electrical power on board a Qantas Boeing 747-400 last month was not as serious as first indications suggested.

During descent to Bangkok airport on 7 January, the cabin crew reported a water leak in the forward galley, quickly followed by several electrical bus and system failures. Some flight instruments were degraded or blanked, but the aircraft landed safely about 20min later.

In an interim factual bulletin, the Australian Transport Safety Bureau says the incident was "less serious than first reported". It has issued no further advisories beyond the operator message sent on 11 January recommending inspection of the fibreglass drip-shields above the main avionic equipment centre below the galley to protect it from fluids. There was a crack in the drip-shield on the incident aircraft, and Qantas found cracks in 14 others out of its fleet of 30.

Inspection of the 747's galley water-drainage system revealed that a ribbon heater - designed to prevent icing of the waste-water external drain-mast - was not functioning, and the drain tube was split. Qantas's fleet inspection revealed six failed drain-mast heaters and two split hoses.

The Qantas incident involved loss of power from three of the four alternating-current buses, automatic disengagement of the auto-throttle and autopilot, blanking of the first officer's displays and several pages of messages on the engine indicating and crew alerting system. The captain's primary flight display and navigation display were available - although in a degraded mode - as were standby instruments. Some of the aircraft's systems reverted to battery power.

Source: Flight International