What about passengers' cellphones? Could they be tracked?
The reason you can be tracked on land is because your phone is constantly talking to the cell towers that provide you service. No service? No location. While you're in the air, there's not much of an opportunity to use your cellular network — although that's changing in Europe and may soon begin to change in the United States, too. Technology now enables the use of cellular networks if a plane carries a special base station that sends communications to a commercial satellite, which then relays it to the ground. But adoption will be voluntary among airlines.
Don't phones often carry GPS chips?
Good thought. Yes, many cellphones do have GPS. But it's not the kind you'd find in a car. Cellphones typically rely on a kind of "assisted" GPS — one that requires a constant data connection. Without WiFi or a cell tower, you're not able to connect with the satellite.
Did Flight 370 have WiFi?
WiFi would almost certainly have helped. Mobile devices on the plane would have been communicating with the Internet right up until its other communications systems went down. But Malaysia Airlines does not appear to offer in-flight WiFi.
What other technologies might have helped maintain a fix?
The Federal Aviation Administration (FAA) wants to transition to a next-generation air traffic control system that uses GPS satellites to keep tabs on planes. It's called, appropriately, Next Gen. Satellites have a distinct advantage over radar — a technology that dates back to World War II — in that they can monitor wide swaths of territory, including oceans. Unfortunately, this system is still years away. Even if we had it now, the FAA is mainly concerned with domestic airspace. Malaysia Airlines would not have been covered. Someday, however, a worldwide version of Next Gen might prevent any future Flight 370s.
Speaking of satellites, U.S. officials have examined spy satellite imagery from the region and have turned up no clues about what happened to the plane.