Investigators use hydrophone to search for AirAsia plane

Singapore investigators taking on a daunting at-sea search for a missing AirAsia flight explain how they are using their tools of the trade.

The flight is presumed to have crashed off the Indonesian coast Sunday with 162 on board, en route from Indonesia to Singapore.

The possibility that the plane is on the bottom of the ocean complicates the search.

Investigator Steven Teo.

(SOUNDBITE) (English) SINGAPORE AIR ACCIDENT INVESTIGATION BUREAU SENIOR INVESTIGATOR STEVEN TEO SAYING:

"So typically, flight data recorders are affixed with an underwater locator beacon or ULB for short. How this works is, when it is submerged underwater, it will emit an acoustic signal of 37.5 kilohertz at every one second interval. So what we do to pick up this signal is, we have this device called the hydrophone, we will submerge the hydrophone underwater and rotate it 360 degrees. We have another operator on a small boat to listen out for the detector signal."

The plane di