A friend recently asked why cell phones are supposed to be off during a flight.

Oh, I know ALL ABOUT this. I have sources and everything. Prepare yourself for the low-down.

First of all, it’s worth noting that there are two federal agencies involved, the FAA (which regulates air travel) and the FCC (which regulates radio). That’s a big part of why this particular issue (personal use of radio while traveling by air) is so legally complex.

Let’s start with the history. The FAA ban on Personal Electronic Devices (PEDs) was instituted in May 1961 because of concerns regarding passenger use of FM radio [1]. At the time, one of the principal means of aircraft navigation was the use of ground-based beacons operating in the VHF Omnidirectional Range (VOR), 108-118 MHz [2]. If you’ve used an FM radio lately(?!), you know that the range of stations is 85-108 MHz. So, if your FM radio is tuned to 108 MHz, and your aircraft has a VOR receiver tuned to 108.05 MHz, it is entirely plausible that the FM radio will rebroadcast the FM music signal with a near-field broad spectrum that drowns out the 108.05 MHz VOR that the aircraft navigation system is trying to listen to. So the FAA said that if you’re flying an aircraft using VOR navigation, you better not allow anyone in the cabin to turn on an FM radio. As people began to carry around more Personal Electronic Devices - Walkmans, Gameboys, etc. - those became subsumed in the FAA’s ban as well, out of general caution [1], although the FAA allows aircraft operators to make their own exceptions to the ban as they see fit [4, paragraph (b)(5)]. Meanwhile, the FCC licenses air-to-ground radios separately from land radios, in large part because signals transmitted from the air have the potential to interfere with a much wider swath of land than would be possible from the ground, so in 1991, the FCC explicitly disallowed the use of (land-licensed) cell phones from onboard aircraft [3], partly in response to the FAA’s nagging and partly in response to land-radio licensees who were asking if they could operate from balloons and such.

Therefore, the current situation is that the operation of cellular phones during flight is forbidden separately by both FAA and FCC regulations. Industry standard rules about taxi, takeoff and landing and the magic 10,000-feet number seem to derive from the FAA’s non-binding advice to aircraft operators [1], which is justified on the basis of both the increased risk to aircraft safety if navigational equipment should fail while the plane is close to the ground, as well as the increased risk to personal safety in case of a botched landing if someone is listening to their Walkman and not paying attention when the crew is asking them to brace for impact.

It is worth noting that there is strong evidence that one particular phone, the Samsung SPH-N300, is capable of jamming an aircraft GPS receiver [7], thanks to sideband interference. The SPH-N300 is in compliance with all relevant FCC regulations limiting harmful interference from land-based radio devices, but severely exceeds the FAA’s safety margins for aviation electronics; and it has been demonstrated that switching on the phone in the cockpit of a specific aircraft effectively disables that aircraft’s GPS. Moving the phone behind a solid metal object (such as, say, the typical cockpit door) removes the interference and restores the GPS to its normal function; but this is still worthy cause for concern. There has been circumstantial evidence of other interference [12].

The FAA commissioned a rule-making committee last year to revisit their regulations on Personal Electronic Devices [8], due to widespread consumer complaints, including a perceived double standard since pilots are now allowed to use iPads even in the cockpit (though all wireless functions must be turned off at all times) [9]. They will not consider the possibility of actually placing a phone call from a commercial flight [8]; cell networks would fight such a change [10], probably for the same sort of reason they routinely produce short films asking moviegoers to switch their phones off. However, the Chairman of the FCC has written a letter to the FAA [11] supporting reconsideration of the ban on electronic devices e.g. during takeoff and landing. (That said, the FCC has shown no interest in allowing actual cellular communications during flight; they simply see no reason not to allow devices in “airplane mode” during takeoff and landing, as currently allowed above 10,000 feet.) This rule-making activity is still underway as of this week [13].

Amusingly, the FAA ban on personal electronic devices specifically exempts portable voice recorders and electric shavers, alongside hearing aids and heart pacemakers [4]. However, noncompliance with crewmember instructions is considered a federal offense in its own right [5] under 14 CFR 91.11 [6], so an airline can essentially ban whatever they want whenever they want and you are legally obligated to comply.

[1] http://ashsd.afacwa.org/docs/AC91-21-1A.pdf
[2] http://en.wikipedia.org/wiki/VHF_omnidirectional_range
[3] http://digital.library.unt.edu/ark:/67531/metadc1883/m1/40/
[4] http://www.ecfr.gov/cgi-bin/text-idx?node=14:
[5] http://www.criminaldefenselawyer.com/resources/interfering-with-a-flight-attendant-or-crewmember.htm
[6] http://www.ecfr.gov/cgi-bin/text-idx?node=14:
[7] http://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-2004-tm213001.pdf
[8] http://thehill.com/blogs/transportation-report/aviation/245703-faa-to-study-allowing-electronic-devices-use-in-flight
[9] http://bits.blogs.nytimes.com/2011/12/14/f-a-a-approves-ipads-in-cockpits-but-not-for-passengers/
[10] http://money.cnn.com/2005/06/16/technology/personaltech/cingular_inflight_calls/
[11] http://bits.blogs.nytimes.com/2012/12/06/fcc-calls-on-faa-to-allow-electronics-on-planes/
[12] http://asrs.arc.nasa.gov/docs/rpsts/ped.pdf

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