As the recent flurry of articles about why portable electronic devices are restricted during air travel makes clear, the conclusion to be drawn from the information available is a very complicated: "We just don't know." For this reason alone airlines err on the side of caution, asking people nicely (and sometimes not so nicely) to turn off their gadgets during takeoff and landing.

Here's what we do know, or at least here's what makes sense and comes from reputable sources, including the U.S. Federal Aviation Administration (FAA):

1. Radio-frequency emissions from cell phones, laptops and other electronics can occur at the same frequencies used by aircraft communication, navigation and surveillance radio receivers. These emissions could cause fluctuations in navigation readouts, problems with other flight displays, and interference with air traffic communications.

2. It's less risky to let passengers use portable electronics (with the exception of cell phones) at cruising altitudes above 3,000 meters* because the flight crew would have more time to diagnose and address any possible interference than they would during takeoff or landing.

3. Because passengers bring such a variety of portable electronics onboard in so many different states of function or disrepair, the FAA can't assure that none of them will interfere with flight instrumentation. The agency thus tells carriers to prohibit their use completely during critical phases of flight.

4. The FAA has begun allowing flight crews to use tablet computers including iPads in the cockpit. But this is not as surprising as it might sound: Crews have actually been using portable computers called "electronic flight bags" since the early 1990s to replace printed aircraft operating manuals, flight crew operating manuals and navigational charts.

5. Portable voice recorders, hearing aids, electric shavers and heart pacemakers do not need to be shut off at any time during a flight because their signals don't interfere with aircraft systems.

6. For any gadget not specifically mentioned by FAA rules, an airline must demonstrate that this device doesn't interfere with aircraft operation before it is allowed on board.

7. The U.S. Federal Communications Commission (FCC) has banned the inflight use of 800 MHz cell phones since 1991 to keep cell networks from interfering with airplane instrumentation. (Before that cell phones were banned because they didn't fit in the overhead luggage compartment or safely under a passenger's seat.)

8. The FCC and FAA work in tandem to ban cell phones on airplanes. Even if a cell phone were to meet the FAA's safety requirements, an airline would need an exemption from the FCC rule for that cell phone to be used inflight. Likewise, if the FCC rescinds its ban, the FAA would require an airline to show that the use of a specific model of phone won't interfere with the navigation and communications systems of the specific type of aircraft on which it would be used.

9. RTCA, Inc., a Washington, D.C.-based federal advisory group, concluded that the FAA should keep its inflight restrictions in place after the group studied electromagnetic interference from cell phones and Wi-Fi transmitters in laptops from 2003 to 2006. At the same time, RTCA also published detailed processes that carriers and electronics makers can follow to certify such devices for inflight use if desired.

10. Airlines may offer inflight Wi-Fi between takeoff and landing. The FAA doesn't restrict the use of Skype or other Internet calling software. (Airlines, however, have banned them for the sanity of their crew and passengers.)

Image courtesy of Gene Chutka, via

*(12/22/11) This sentence was edited after posting. It originally presented the altitude in kilometers. The sentence should read "3,000 meters".