# Why do Planes nix cell phones, lapstops, etc? **URL:** \ **Category:** Factual Questions\ **Created:** [March 1, 2000, 4:40pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967 "2000-03-01T16:40:00Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![BuddyG](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@BuddyG](https://boards.straightdope.com/u/BuddyG)\ **Post date:** [March 1, 2000, 4:40pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/1 "2000-03-01T16:40:00Z")
During a recent trip, while sitting on a jet, the flight attendant made the usual safety speech which included the admonition that passengers NOT use cell phones, laptop computers, or other electronic devices such as GameBoys while the aircraft was at the gate. There was vague mention that it could interfere with their radio communications. When the flight was airborne, laptop use was permitted, but not cell phones. Although seatback “Airphones” were available. Are personal cell phones, laptops, etc really that dangerous to planes? Why? * * * All you touch and all you see is all your life will ever be… ---
**Author:** ![pluto](https://avatars.discourse-cdn.com/v4/letter/p/f08c70/32.png) [@pluto](https://boards.straightdope.com/u/pluto)\ **Post date:** [March 1, 2000, 5:58pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/2 "2000-03-01T17:58:00Z")
There is an _extremely_ remote possibility that these devices could cause unexpected electrical interference with the aircraft wiring. The likelihood of a problem developing is practically nil, but it isn’t precisely nil. Hence the prohibition. To give you some idea of how remote the possibility is recall that they do allow you to use the devices once they reach cruising altitude. The possibility of interference hasn’t gone away, but now the presumption is that if something untoward should occur they will have time to fix it. During takeoff or landing timing is more critical and the FAA gets nervous then, just like my wife. Further, they’re not concerned about interference with the actual control of the airplane. No commercial aircraft uses a fly-by-wire system that is susceptible to this interference. Most commercial jets use hydraulic and/or cable systems. Those that are fly-by-wire either use fiber optics (which are not subject to electrical interference) or wires that are so well shielded you couldn’t disrupt them with an EMP from a nuclear device. What you can (theoretically) interfere with is communications and/or signals from the various parts of the aircraft. You might be playing your Game Boy and send out a signal that somehow gets interpreted in the cockpit as an out-of-fuel indicator or something similar. The crew panics and aborts the flight. There was no real danger, but a lot of expense and annoyed passengers, as well as laundry bills for the crew. The aircraft equipment is shielded to prevent this, of course, but when the issue is the safety of hundreds of people they’re going to err on the side of caution. So put your CD player away and read the entertaining complimentary airline magazine for a while. * * * he sleeps on that pile/of newspapers/in the corner/and when he takes off his/shoes you cannot/smell his breath “king nicky”, _archyology_ Don Marquis ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [March 2, 2000, 6:24am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/3 "2000-03-02T06:24:00Z")
- - - FAA regulations state that it is illegal to use a cellphone while in the air. Cellphone companies wanted it this way: they specifically asked for this law. Cellphone towers always listen for cellphone signals and if the signal is above a certain threshold, that tower tries to receive that phone’s signal. It also “asks” the towers in the surrounding cells if any of them are getting that particular signal stronger than it is; if any other is getting a stronger signal, then that call is transferred to that tower, because it is presumed that the phone is actually closer to being in that tower’s cell area. The “cells” (the area of one tower’s coverage that you can roam in without being handed-off to another tower) are mapped out so that as you near the edge of the present cell you are in, your signal begins to get weak to that tower, but begins to get stronger to the tower of the cell you are entering. Now because of this arrangement, if you’re on the ground, your phone’s signal can’t ever be between more than three cells at a time. The towers are spaced out far enough that accounting for interference and absorption of ground objects, no other towers will detect your phone’s signal enough to bother trying to actually receive it. Sooooo, the computer software that governs when and how cellphone use is switched between adjoining cells (towers) is only really designed to deal with triads of towers. When any tower detects your phone signal, the tower asks all its neighbors if they are getting that particular signal better, and expects to find at most only two other towers detecting your phonecall. These three towers “share” signal info, and whichever gets the signal strongest, gets “handed” the call. - If you’re in an airplane though, this situation changes: the signal that your cellphone gives off can easily reach more than three towers at once. The problem is not that your phone won’t work; it’s that your phone will reach more than three towers and none can easily figure out which should receive the call. What usually happens is your call goes through on one tower like normal, but other towers tie up processing time because they get brain freeze; they try to “take” the call off of each other and when they can’t, they generate scary error messages at the cellphone company’s computer system. - MC ---
**Author:** ![frolix8](https://avatars.discourse-cdn.com/v4/letter/f/f04885/32.png) [@frolix8](https://boards.straightdope.com/u/frolix8)\ **Post date:** [March 1, 2000, 11:03pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/4 "2000-03-01T23:03:00Z")
A recent Wall Street Journal article claimed it was mainly financial, the airlines get a cut of the 3$ per minute charge for the sky phones. I hope they keep it that way, flying is unpleasent enough already, imagine if every other person was carrying on a loud conversation on their phone. (Like they do as soon as they get off the plane) This topic comes up often in Aviation Week. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [March 1, 2000, 11:06pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/5 "2000-03-01T23:06:00Z")
Golly–and all I tried to do was use my little Walkman to play tapes. And the stewardess told us there were specific times during the flight when we had to turn them off. ---
**Author:** ![Beruang](https://avatars.discourse-cdn.com/v4/letter/b/77aa72/32.png) [@Beruang](https://boards.straightdope.com/u/Beruang)\ **Post date:** [March 1, 2000, 11:20pm UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/6 "2000-03-01T23:20:00Z")
Not strictly on topic, but related info may be found at [http://www.straightdope.com/classics/a2\_355.html](http://www.straightdope.com/classics/a2_355.html) * * * “The dawn of a new era is felt and not measured.” Walter Lord ---
**Author:** ![Oblio](https://avatars.discourse-cdn.com/v4/letter/o/c4cdca/32.png) [@Oblio](https://boards.straightdope.com/u/Oblio)\ **Post date:** [March 2, 2000, 1:34am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/7 "2000-03-02T01:34:00Z")
MC: > [@](#): > > FAA regulations state that it is illegal to use a cellphone while in the air. Please cite the FAR that prohibits me as an aircraft owner/operator (or a passenger with the airlines permission) to operate a cell phone while in flight. I don’t mean to be sarcastic, I’ve heard many conflicting opinions concerning this. Just want the straight dope. * * * A point in every direction is like no point at all ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 2, 2000, 2:48am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/8 "2000-03-02T02:48:00Z")
The use of cell phones in flight is not prohibited by the FARs. It is an FCC regulation. Regarding portable electronic devices, see the FAA Advisory circular here: [http://www.bts.gov/NTL/DOCS/91-21\_1.html](http://www.bts.gov/NTL/DOCS/91-21_1.html) [quote] Subject: USE OF PORTABLE ELECTRONIC DEVICES ABOARD AIRCRAFT 1. PURPOSE. This advisory circular (AC) provides aircraft assistance in the compliance of Federal Aviation Regulations (FAR) Section 91.21. Because of the potential for portable electronic devices to interfere with aircraft communications and navigation equipment, FAR Section 91.21 was established. It prohibits the operation of portable electronic devices aboard U.S.-registered civil aircraft, operated by the holder of an air carrier operating certificate or an operating certificate, or any other aircraft while operating under instrument flight rules. The rule permits use of specified portable electronic devices and other devices that the operator of the aircraft has determined will not cause interference with the safe operation of the aircraft in which it is operated. The recommendations contained herein are one means, but not the only means, of complying with the requirements of FAR Section 91.21, pertaining to the operation of portable electronic devices.[/iquote] ---
**Author:** ![NanoByte](https://avatars.discourse-cdn.com/v4/letter/n/ecc23a/32.png) [@NanoByte](https://boards.straightdope.com/u/NanoByte)\ **Post date:** [March 2, 2000, 3:08am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/9 "2000-03-02T03:08:00Z")
So is a “lapstop” something to keep a kid from sliding off one’s lap? Ray ---
**Author:** ![NanoByte](https://avatars.discourse-cdn.com/v4/letter/n/ecc23a/32.png) [@NanoByte](https://boards.straightdope.com/u/NanoByte)\ **Post date:** [March 2, 2000, 3:10am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/10 "2000-03-02T03:10:00Z")
So is a “lapstop” something to keep a kid from sliding off one’s lap? Ray ---
**Author:** ![NanoByte](https://avatars.discourse-cdn.com/v4/letter/n/ecc23a/32.png) [@NanoByte](https://boards.straightdope.com/u/NanoByte)\ **Post date:** [March 2, 2000, 3:16am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/11 "2000-03-02T03:16:00Z")
Sorry, but what the software needs is some kind of feedback that the server has received the post, even though it isn’t yet displayed on the reloaded page. I suppose, if you could do that soon enough, you could get the post **posted** soon enough to avoid confusion to the poster, though. Maybe there’s a way to raise a clear flag when traffic is heavy. Ray ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 2, 2000, 3:35am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/12 "2000-03-02T03:35:00Z")
I guess I’ll go ahead and post **FAR 91.21 Portable Electronic Devices** : > [@](#): > > (a) Except as provided in paragraph (b) of this section, **no person may operate, nor may any operator or pilot in command of an aircraft allow the operation of, a portable electronic device on any of the following U.S.-registered civil aircraft:** > (1) Aircraft operated by a holder of an air carrier operating certificate; or > (2) Any aircraft while it is operated under IFR. > (b) Paragraph (a) of this section **does not apply to –** > (1) Portable voice recorders; > (2) Hearing aids; > (3) Heart pacemakers; > (4) Electric shavers; or > (5) **Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft** on which it is to be used. > © In the case of an aircraft operated by a holder of an air carrier operating certificate or an operating certificate, the determination required by paragraph (b)(5) of this section **shall be made by the operator** of the aircraft on which the particular device is to be used. In the case of other aircraft, the determination may be made **by the pilot in command** or other operator of the aircraft. (Bolding added by me.) ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [March 2, 2000, 5:04am UTC](https://boards.straightdope.com/t/why-do-planes-nix-cell-phones-lapstops-etc/7967/13 "2000-03-02T05:04:00Z")
> [@](#): > > The use of cell phones in flight is not prohibited by the FARs. It is an FCC regulation. - Johhny LA - - - Well, all those federal people look alike to me. - MC