Blocked drain put Qantas jet at risk

Overflowing water from two galleys and toilets had seeped through the floor of flight QF2 from London as it was descending on Bangkok airport, short-circuiting three of the four onboard power generators.

The Australian Transport Safety Bureau's final report released yesterday into the January 7, 2008, incident found moisture vulnerabilities to the Boeing 747's electrical power units, as well as information gaps in emergency flight manuals and automatic computer warnings for pilots facing onboard electrical shutdown.

The overflow was traced to an ice "plug" that formed in a drain pipe, due to a broken drainpipe heater.

The flood knocked out radar, cabin pressurisation, auto-pilot, auto-throttle and some fuel pumps.

The pilots decided not to declare an emergency landing, an action investigators think ought to have been taken.

The flight was running on its 30-minute store of battery power for its last 15 minutes, and had been on batteries for 21 minutes by the time the aircraft landed and taxied to the terminal building, investigators found.

If the flooding had occurred more than 30 minutes from landing, it would have placed the plane carrying 346 passengers and 19 crew "at considerable risk" as more flight systems were likely to have failed, investigators said.

Next to fail would have been the plane's communications, air speed, altitude and heading displays, warning systems, navigation and engine instrumentation.

It was difficult for pilots to know how much battery power was left.

The pilots managed to land the ailing craft safely without injuries, but when the engines were shut down, the cabin lighting cut out and the doors could not be opened because the cabin remained pressurised a serious problem in any emergency evacuation.

In response to the investigation, the bureau said "Qantas, Boeing and the US Federal Aviation Administration have implemented a number of safety actions to prevent a recurrence," including reinforcing dripshields above electrical equipment, better maintenance practices and pilot training and installing advanced "standby" 747 flight instruments.