Air France 447 - Why satellites didn't find missing plane
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(CNN) -- Cars have Global Positioning System devices to pinpoint where drivers are when they get lost, so why can't GPS be used to locate the exact position of planes when the worst happens?
There is no constant tracking of planes when they go oceanic, although a sytem is being developed.
Although details of Flight 447's fate remain uncertain, in some air accidents, this critical time could mean the difference between life and death for any survivors.
Michel Roelandt, aviation expert for Eurocontrol, a European air navigation safety organization, told CNN that some planes are fitted with GPS systems, but these are essentially "dumb" units -- like those in cars -- that receive location information from satellites but do not send any data back.
So while a flight crew knows its exact position over an ocean, the information is not automatically sent to air traffic control. That is left to someone in the cockpit to relay via satellite communication when the plane is out of radar range. 
Read more about how flights are tracked »
According to industry experts, satellite technology that would allow constant monitoring of an aircraft's exact position is available, and although plans are afoot to introduce it, cost may be deterring some airlines.
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"Airlines often have a contract with a private operator to provide their satellite communications. Some companies pay for it, some have free contracts," Roelandt said.
The United States owns most of the GPS satellites in space that track the positions of commercial aircraft. As long as an airplane is within range of two to three satellites in space, it uses them to triangulate its position and send the information to the nearest ground station via a transponder, said Bill Waldock, professor of safety science at Embry Riddle University in Prescott, Florida.
It's also possible, although unlikely, that the location of a troubled aircraft could be pinpointed by military defense satellites, experts said.
Some U.S. military satellites employ heat-sensitive cameras that scan the skies for missiles and could possibly detect a plane if it were not obscured by clouds, said John Pike, director of GlobalSecurity.org, a public policy organization whose Web site provides news on weapons systems and the defense industry.
Roelandt stressed that the idea of GPS tracking has not been part of any safety review within the aviation industry. The general consensus has been that a trained flight crew is on hand that always has the capability to be in contact with someone on the ground should an emergency arise.
In the case of Air France Flight 447, it appears that the crew had no time to relay an emergency message.
Shortly before the plane disappeared, its automatic system initiated a four-minute exchange of messages to Air France's maintenance computers, indicating that "several pieces of aircraft equipment were at fault or had broken down," Air France CEO Pierre-Henri Gourgeon said on Monday.
"Usually these data reports send information on normal systems, things like what the in-flight entertainment is doing, or that the cabin temperature has dropped by a few degrees," said Kieran Daly of Air Transport Intelligence, an online aviation news service.
"It's like your car telling you something is wrong, but in this case the A330-200 sent out a signal to Paris, basically warning that when it arrives in X number of hours, this is what's wrong with the plane," said CNN's Richard Quest. "It was the automatic system on the plane telling Air France headquarters we've got a problem."
Based on the aircraft's route and the timing of the data reports, search and rescue teams could know where, roughly, to look for the plane.
Upgrading from radar to satellite system
The aviation industry is moving toward replacing its traditional radar-based tracking system with a satellite one that would allow air traffic control to know where a plane is at all times, even over oceans.
The U.S. Federal Aviation Administration has begun implementing a system, nicknamed NextGen, in which GPS signals would transmit an aircraft's precise location to air traffic controllers via ground receivers. The system would allow planes to fly more direct routes instead of zig-zagging between radio beacons.
The FAA is testing the system in pockets of the U.S. and plans to be using it by the end of the year in the Gulf of Mexico, much of which is out of radar range. The agency hopes NextGen will cover the entire country by 2013.
Roelandt says a similar system will be implemented in Europe by 2015.
"It means planes will automatically transmit the GPS position to the ground and surrounding aircraft within about 150 miles," he said. "In the far future the idea is to be in a free flight condition," where pilots have more flexibility in their routes while GPS keeps planes safely separated.
In a trial last year using an Automatic Dependent Surveillance-Broadcast system, two Airbus planes were able to change altitude safely while cruising over oceanic airspace.
At present, airliners flying over oceans are usually not permitted to change altitude, because oceanic airspace beyond a certain distance from land cannot be controlled by radar. Controllers and pilots keep the planes on vectors, or defined highways in the sky, to maintain safe distances between aircraft.
The ADS-B system is being developed internationally. But the expense of outfitting planes with GPS is dwarfed by the cost to upgrade from radar to satellite tracking of planes. According to a 2006 FAA report, it would cost $4.6 billion to change to a satellite-based system in the U.S.
"It's a bit of a chicken and egg situation," Roelandt said. "If you don't put an implementing rule on this equipment, airlines won't install it as it's a costly operation for them. It is ongoing, and will be installed on European commercial airliners, but it takes time as always."
CNN's Brandon Griggs and Emanuella Grinberg contributed to this story.
