Hard to Find Missing Planes, Even With Advanced Technology

The search for AirAsia Flight QZ8501 has again drawn attention to how difficult it can be to find a missing plane despite advanced technology.

It's not completely clear what kind of tracking devices were available on the missing Air Asia Flight, but experts say even with some of the best technology it can still be difficult to locate a downed plane immediately.

Experts say the plane would have had a transponder to communicate with radar run by air traffic control during the flight

The transponder works by alerting air traffic control about the plane's location and its altitude.

"Radar sends a signal saying 'Who are you?' and aircraft sends a signal back," said aviation consultant Alan Diehl, who has worked with the National Transportation Safety Board.

The plane would also likely have an aircraft communication system that lets the pilots and air traffic control dispatchers send messages digitally, Diehl said.

If the transponder is disabled, either by someone on board or due to a crash, then air traffic control could look for unidentified signals on radar to see if the plane might still be in the air, Diehl said.

John Nance, aviation analyst for ABC News and veteran airline captain, said the AirAsia plane might be located through its emergency beacon if it crashed.

The beacon, which transmits a signal either through contacting a satellite or by sending a message on radio waves in the event of a crash, is designed to help authorities find missing planes, but Nance said it doesn't work well if it is not thrown free from the wreckage.

Nance also said in the past the beacons have been most helpful for crashes on land.

As a result, search planes and rescue ships have to transverse large areas close to where the plane disappeared from radar, as they did with Malaysian Airlines Flight MH 370.

In the case of Flight MH 370, after the transponder was disabled the plane remained in the air. While the plane was still flying, it was not directly communicating with air traffic control to alert them of its location and its altitude.

The Malaysian Airlines flight also had a key piece of equipment from telecommunications company Inmarsat that allowed the plane to "ping" a satellite even after the transponder was disabled.

As a result of data gathered by Inmarsat, authorities were able to eventually find that MH370 flew for hours after the transponder was disabled and likely crashed in the Indian Ocean.

However, the missing AirAsia flight was not outfitted with Inmarsat technology, according to an email from Inmarsat spokesman Chris McLaughlin.

In the event no sign of the plane is found, the search team can use underwater microphones to see if they can hear a ping from the plane's black boxes. Each has a 30-day underwater locater pinger that could allow ships to locate jetliner more easily.