It's a fact of life for the frequent flier: Once the plane is off the ground, cell phones must be turned off and put away.
That's the rule and every commercial airline in the United States enforces it. But is there a good reason for this? Can a cell phone bring down a plane, or is that just a myth?
"The evidence strongly supports that there is a risk," said Bill Strauss, an electromagnetic interference expert.
According to Strauss, cell phones emit strong radio signals that could cause false readouts on an airplane's navigational equipment. Strauss and other researchers from Carnegie Mellon University invented a device that detects radio emissions from cell phones and other electronic devices. They tested 37 commercial flights and learned that on each flight between one to four cell phone calls were placed. But do those rule-breaking cell phones really affect the plane's equipment?
The answer is unclear.
An aviation safety database maintained by NASA shows a handful of incidents each year reported by pilots who suspected cell phones and other electronic devices had caused a problem during flight. Despite these reports, not a single air crash has been proven to be caused by the use of a cell phone onboard a plane.
John Nance, an ABC News consultant and veteran airline pilot, says there's little reason to worry about cell phones interfering with an airplane's navigational equipment. He says an airplane's electronic systems are "all heavily shielded. That means that stray signals cannot get into those systems."
But don't break out those cell phones just yet. The airlines can't allow cell phones to be used in flight until the technology has been proven safe. However, according to Nance, the Federal Communications Commission and the Federal Aviation Administration "have not done their job over about a 25-year period. And the airlines have quite properly said … if you're not going to tell us, then we're just going to default to the most conservative position and say we're not going to use them in the air."
The FAA told ABC News it has been collecting more data; the FCC said safety is the FAA's responsibility. Though the agencies may not be ready to allow cell phones on airplanes here, the rules have already changed in Europe.
The European Aviation Safety Agency has approved a technology that reduces the risk of interference with airplane electronics. Several European airlines will allow passengers to use cell phones in their skies, as well as wireless Internet, starting in 2008. Airlines in the United States will begin using a similar technology next year, but because cell phone use is still banned, the service can be used only for wireless Internet access.
So while there isn't proof that a cell phone can bring down a plane, until the FAA and the FCC say using cell phones in flight is safe, it's probably best to just keep those gadgets off.