In January, 1993, a passenger flight from Denver to Newark, N.J., was proceeding smoothly at cruise altitude when the aircraft's directional gyros abruptly stopped working. The pilot, moving quickly to avert a crisis, instructed a flight attendant to tell passengers that they must immediately turn off all radios, tape recorders, laptop computers, and video game players. She returned to tell the pilot that 25 passengers had been listening to a football game on their radios. One passenger had been using a laptop.
The pilot waited for the gyros to return, but the malfunction continued. He asked the flight attendant to make sure the radios had been turned off. She returned to the cabin and found that the passengers had ignored her instructions--the radios were still on. The captain announced by loudspeaker that the radios were affecting navigation equipment and must be turned off. In about 90 seconds, the gyros corrected themselves to the proper headings.
The crisis had passed. But 20 minutes later, the gyros "began moving off [the] correct heading by as much as 20 to 30 degrees," according to a NASA report on the incident. The captain warned that he would confiscate all radios if the problem persisted. Within two minutes, the gyros swung back to the correct heading. No further incidents occurred, according to the report by NASA's Aviation Safety Reporting System. The report did not disclose the name of the airline involved.
The gyro errors might have had nothing to do with the radios in the cabin. Coincidences do occur, and an investigation was unable to explain how the radios could have affected the gyros. But there have been enough of those cases in recent years to raise serious concerns. Since 1982, pilots have reported at least 137 in-flight incidents that could have been caused by electromagnetic interference from portable electronic devices, according to RTCA Inc., a nonprofit organization that advises the aviation industry. That figure comes from RTCA's review of its own databases and those of NASA and the International Air Transport Assn. Since these are voluntary reports, the actual number of such incidents may be higher, experts say. With the continuing proliferation of portable electronics--laptops, personal stereos, handheld game machines, and the like--the concerns are growing.
In a new report, RTCA recommends the toughest-ever restrictions on the use of portable electronic devices on board aircraft--a ban on the use of portable electronic devices during "all critical phases of flight." That would include takeoffs and landings, the times when there is the least room for error. Some experts are so concerned about the danger that they have called for a complete ban on all devices during flight.
Right now, the Federal Aviation Administration leaves the decision up to individual airlines. It also gives airlines all responsibility for monitoring and approving various electronic equipment, requiring them to test devices and ban any that could cause interference. But RTCA Special Committee 177 Chairman John Sheehan says the FAA rule has been unenforceable and almost impossible for the airlines to carry out. "FAA came up with a regulation that neither it nor the airlines could comply with," says Sheehan. The FAA says that reports of problems have trailed off since 1993, when it advised airlines to restrict the use of portable electronic devices below 10,000 feet.
NERVOUS TIME. The takeoff and landing rule applies to laptops and other portable electronic devices that emit electromagnetic radiation as an unintended byproduct of their operation. In addition, the RTCA committee recommends a total ban on devices designed to transmit radio waves. One example would be a pager that automatically acknowledges receipt of messages by sending a signal back. Another would be a wireless modem on a laptop computer. Cellular phones are also covered, but they are already banned from aircraft because they interfere with cellular networks as they fly over them.
The interference problem creates uneasiness for airlines. On the one hand, they want to ensure safety. On the other, they want to satisfy passengers' urge to keep busy aloft. American Airlines Inc. recently announced that starting in January, it will begin equipping seats in some first-class and business-class sections with power supplies for items such as laptop computers and compact-disk players. To avoid takeoff and landing problems, the power will be turned on only above 10,000 feet. As other airlines follow suit, the power of portable electronic devices will be less and less constrained by batteries.
The trade-off between safety and convenience is hard to measure because no one knows how dangerous interference is. In one case, it may have been fatal. British authorities suspect that electromagnetic interference from a laptop computer, camcorder, or cell phone might have sparked a fatal 1991 Lauda Air accident in which one of the plane's computers mysteriously activated the reverse thrusters of a Boeing 767-300 shortly after takeoff from Bangkok. The crash claimed the lives of all 223 people on board, and its cause remains unexplained. "Nothing has been proven on that at all. There are a lot of different suspicions," says Mary Jean Olsen, a Boeing Co. spokeswoman.
The uncertainty surrounding the harmfulness of portable electronic devices stems from the unpredictability of electromagnetic fields. During exhaustive tests, investigators have often been unable to replicate a reported interference in a controlled environment. "It's like taking a bunch of Superballs and bouncing them into a corner. It's possible to rig it to get the same random bouncing twice, but it's very difficult. And you're talking about a lot of money. Who's going to pay for this?" says RTCA committee member Finbarr M. O'Connor Jr. Adds Bruce J. Donham, an electromagnetics engineer at Boeing: "Eight different simultaneous events have to occur. Everything has to line up perfect or you won't see it."
Some of the strongest electromagnetic fields can come from laptop computers. Even though they are built with shielding to prevent unintended radio emissions, the shielding on some deteriorates over time, allowing radio waves to leak out. A laptop with a 90-Mhz microprocessor will give off radiation at that frequency as well as at higher, so-called harmonic frequencies. Tape players and video game machines emit waves lower down the frequency spectrum. Strong signals can be emitted by devices with unshielded wires hanging from them--such as the cord for a headset or a computer mouse--because the wires can radiate like antennas.
Overall, the portable gear emits radiation across a big swath of the spectrum airplanes use for navigation and communication. Radio waves can leak through cabin windows and jam the signals that the plane's antennas receive from beacons on the ground, says Orville Nyhus, an aeronautical engineer for Honeywell Inc., which makes avionics gear. "This is a real threat that causes channel interference, but often people don't take it seriously," Nyhus says.
TOUGH LINE. Some engineers believe the RTCA recommendations don't go far enough. Says Albert Helfrick, an associate professor of engineering technology at Embry-Riddle Aeronautical University in Daytona Beach, Fla., who in 1994 extensively tested fuselage shielding while a member of the RTCA committee: "If it were up to me I wouldn't allow [portable electronic devices] on board aircraft at all, ever."
The vulnerability of aircraft to interference raises a frightening question: What if someone deliberately tampered with the radio systems? Embry-Riddle's Helfrick says that an electronics-savvy terrorist could use a radio transmitter--possibly even from the ground--to sabotage an aircraft's navigational and communications equipment. Terrorism is always difficult to thwart, of course. But airline passengers would rest easier knowing their plane's captain isn't being blinded by someone in 14E trying to call the office on his cell phone.