e-gadgets do cause flight turbulence

But some passengers invariably ignore the request, perhaps thinking that their iPods or e-books do not count. And really, does it matter if the devices are left on?

The answer, it turns out, is that sometimes it may.

“It’s a good news-bad news thing,” said David Carson, an engineer with Boeing. Electronic devices do not cause problems in every case, he said. “And that’s good,” he said. “It’s bad in that people assume it never will.”

Passengers are taking an increasing array of devices on board planes—cellphones, tablets, GPS units and more. Many of these devices transmit a signal, and all of them emit electromagnetic waves, which, in theory, could interfere with the plane’s electronics. At the same time, older planes might not have the best shielding against the latest generation of devices, some engineers said.

“Is it worrisome?” asked Bill Strauss, an engineer who studied passenger use of electronic devices several years ago. “It is.” Safety experts suspect that electronic interference has played a role in some accidents, though that is difficult to prove. One crash in which cellphone interference with airplane navigation was cited as a possible factor involved a charter in Christchurch, New Zealand, in 2003. Eight people died when the plane flew into the ground short of the runway.

The pilot had called home, and the call remained connected for the last three minutes of the flight. In the final report, the New Zealand Transport Accident Investigation Commission stated: “The pilot’s own cellphone might have caused erroneous indications” on a navigational aid.

Since 2000, there have been at least 10 voluntary reports filed by pilots in the US with the Aviation Safety Reporting System, administered by Nasa. In 2007, one pilot recounted an instance when the navigational equipment on his Boeing 737 had failed after takeoff. A flight attendant told a passenger to turn off a hand-held GPS device and the problem on the flight deck went away.

The Federal Aviation Administration says there are risks associated with electromagnetic interference and prohibits the use of electronics below 10,000 feet because pilots have less time at lower altitudes to deal with a problem. It is up to each airline to set the policy at higher altitudes. “There’s not enough evidence to warrant a change,” said Les Dorr, a spokesman for the agency.