(CNN) -- Malaysia Airlines Flight 370 said good night, then drifted off over the darkened seas, somehow bypassing that vast spiderweb of modern technology that catches every move of worldwide aviation. Yet now, high technology seems the only way of tracking down where on Earth the plane ended up.
Let's presume the plane did go down in the Indian Ocean, thousands of feet deep with churning currents and treacherous weather. Here are some devices that might help searchers find signs of the plane.
TPL: Towed pinger locator
One of the most helpful devices planes carry is what's known as the pinger, a "sound" transmitted from the flight data recorder and cockpit voice recorder that can be heard from 2 nautical miles away.
"Think of your cell phone ringer. If you lose your cell phone you can call it and you hear your phone ringing, so you narrow down your search," said Phoenix International manager Paul Nelson. Phoenix International, an American company, owns the TPL-25 system, which dives 20,000 feet below the surface of the ocean for hours and miles at a time.
The U.S. Navy has sent a towed pinger locator, or TPL, to drag behind a ship. The TPL moves at 1 to 5 knots and can recognize the flight recorder's ping up to 20,000 feet below the surface. But it has limitations. The batteries powering the ping will only last 30 to 45 days, and can be drowned out by weather or noise or silt.
In 2009, the Phoenix TPL-25, in conjunction with technology from the Woods Hole Oceanographic Institute, searched for a ping from Air France Flight 447, which crashed hundreds of miles off the coast of Brazil in 2009. That search didn't find the plane, but two years later, searchers found the flight data recorder and the bulk of the wreckage using an autonomous underwater vehicle, or AUV.
AUV: Autonomous underwater vehicles
AUVs are normally used in the oil and gas industry to conduct deepwater oilfield surveys. But when the pinger of the data recorder is dead, the AUV can narrow the search area of a crash site by mapping the ocean floor.
"The smaller ones are only going to go down to about 5,000 feet. The next class is a much more expensive, much larger device. It's 15 by 25 feet because it adds a lot of battery capability and a lot of hydraulic capability," said David Soucie, an analyst who said modern technology has greatly improved the search for answers in a flight crash investigation.
One of the most sophisticated AUVs owned by Phoenix International was activated and flown to Perth, Australia, to help with the search for Flight 370. The device is yellow, 17.2 feet long and has an in-air weight of 1,600 pounds. It can be lowered 20,000 feet below the water surface and travels 2 to 4.5 knots for about 20 hours at a time, using side-scan sonar to create a map of the seafloor. The rapidly moving probe is also equipped with a still camera.
"They have their own control system so they talk to it with an acoustic modem. It's hard to get sound through the water," said Jami Cheramie of C&C Technology, whose AUV has been called in to search for plane debris in the past. "We will see waterfalls. A picture will scroll and you will see the seafloor be painted in front of you."
AUVs are unmanned, so they can be programmed like robots to "mow the lawn," Cheramie said. They use a grid style pattern to create an image of the deep sea. Sensors around the body of the device help it avoid obstacles that would endanger a diver.
AUVs played an instrumental role in finding the downed Air France flight, the plane wreckage of Italian fashion designer Vittorio Missoni off the coast of Venezuela, and the HMS Ark Royal, a ship sunk by a German U-81 submarine in World War II. The AUV provided black and white images of the wreckage site.
Once wreckage is found and confirmed, the next step is recovering key parts, like the data recorders.
ROV: Remotely operating vehicle
The multimillion-dollar remotely operated vehicle provides the "gotcha" moment that all searches are working toward. But investigators need more than just eyes on the wreckage site, they need to get their hands on the data recorders. An ROV helped retrieve pieces of the most famous shipwreck in history, the British passenger liner Titanic.
ROVs are tethered to a ship, lowered by remote control thousands of feet to the ocean floor by a cable and maneuvered by pilots sitting in a control room. The daily rate for an ROV is in the $150,000 range.
Helix Canyon Offshore gave CNN an exclusive look at its Triton XLS ROV aboard the Olympic Triton off the coast of Scotland. The Triton XLS is equipped with cameras that provide a live feed to the control room. It has arms and jaws that can be controlled by a joystick.
"Not a problem at all for an ROV to pick it up, put it in a basket and recover it back to the vessel," said ROV superintendent Martin Stitt.
Posted by Greg Palmer