One of the Navy's Towed Pinger Locators is already en route to the search area.
It's a 30-inch-long cylindrical microphone that's slowly towed underwater in a grid pattern behind a commercial ship. It will pick up any black box ping emitted from, on average, 1 mile away - but could hear a ping from 2 miles away depending upon a number of factors, from ocean conditions to topography to if the black boxes are buried or not.
The listening device is attached to about 20,000 feet of cable and is guided through the ocean depths by a yellow, triangular carrier with a shark fin on top. It looks like a stingray and has a wingspan of 3 feet.
The device sends data up that long cable every half second, where both human operators and computers aboard a ship carefully listen for any strong signals and record a ping's location. The ship keeps towing the device over the grid so that operators can triangulate the strongest pings - and hopefully locate the exact location of the black boxes.
Aside from the Towed Pinger Locator, an Australian navy support vessel, the Ocean Shield, is expected to arrive in the search zone within three or four days, officials said. It's equipped with acoustic detection equipment that will also listen for pings.
If no strong signals are located before the battery on the black boxes fades away, then searchers must move on to using devices called side-scan sonar that creates an X-ray of the ocean floor, allowing experts to look for any abnormalities in the seabed or any shape that wouldn't normally be associated with the area.
The sonar devices can be towed behind a ship or used with unmanned mini submarines that can dive to the ocean floor for about 20 hours at a time, scanning the search area, mapping the ocean floor and looking for the wreckage.
This is how searchers found the wreckage of Air France Flight 447, which went down in 2009 in the Atlantic between Brazil's northeast coast and western Africa. Underwater search vehicles scanned the mountainous sea floor and sent data back up to experts aboard ships that stayed at sea for a month at a time.
Finally, evidence of possible debris was detected by sonar. Another underwater vehicle with a special high-resolution video camera was sent in to allow scientists to visually inspect the area.
In the case of the Air France jet, it took over $40 million, four lengthy searches and nearly two years before the plane and the black boxes were found.
