Hi Everyone,

One of my friends at work was asking about the request to turn all cell phones off when taking a commercial airplane flight. He does not believe that the cell phones, etc. interfere with the operation of the aircraft.

Can someone please provide the technical explanation of why cell phones and other electronic devices need to be off during a flight. Thanks.

Regards,
Melo
PL965 Spitfire pilot,
Glendale, CA

• RE: Cellphones on Airplanes,Ben_Chiu, 18:32z, 06-22-03
  • RE: Cellphones on Airplanes,RobertVA, 06:28z, 06-24-03
    • RE: Cellphones on Airplanes,PL965Melo, 05:04z, 06-25-03
  • RE: Cellphones on Airplanes,PL965Melo, 05:00z, 06-25-03
    • RE: Cellphones on Airplanes,mark_hoffman, 21:34z, 07-07-03

LAST EDITED ON 06-22-03 AT 18:41z ()

Greetings Melo:

> One of my friends at work was asking about the request to turn all cell
> phones off when taking a commercial airplane flight. He does not believe
> that the cell phones, etc. interfere with the operation of the aircraft.
>
> Can someone please provide the technical explanation of why cell phones
> and other electronic devices need to be off during a flight. Thanks.

FAR 91.21 specifies:

"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, any 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 an operating certificate; or
(2) Any other 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.
(c) 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 that 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."

While a single device (like your cell phone) may not cause any interference, the concern is when multiple devices are used together their frequencies can combine and create interference on a new frequency (I think they call it harmonics). Because no one is able to predict every possible combination of every possible device, in the interest of safety, they've banned all devices.

If you have a specific question regarding airline policy, you might try dropping a message in the Airlines and Airliner Forum.

You might try the Aviation Safety Forum as well. I'm sure Pat has the proper technical explanation.

Ben

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Interference with aircraft navigation systems may not be the only concern.

Each analog cell phone conversation requires its own channel in a limited frequency range. No analog phone can use that channel with any cell tower within range of anouther phone on that channel. A plane's altitude would increase the radius of the horizon available to a phone aboard the plane, potentialy bringing more towers into the phone's range. While the low power of pocket size phones is a factor in limiting their range, buildings and other ground based interference often limit their range to a half dozen miles or less, especialy in typical commercial buildings with a metal lined roof or upper floors. In open areas several more miles might become available.

In many urban and suburban areas a phone is probably within range of two or three cells (towers) operated by the customer's vendor as well as several cells operated by other vendors (roaming capability) much of the time. The cells within range increases with dual and triple mode analog/digital handsets. Sometimes several vendors will mount their own seperate cell antennas on a common tower. Some cell antennas are concealed in church spires, the tops of tall buildings, power transmission towers and even large artificial trees.

Digital phones probably share channels (I am not certain) but a phone in a plane would probably add to the conjestion of data packets on a greater than normal quantity of towers.

Robert

Near KORF

Hi Robert,

>> Digital phones probably share channels (I am not certain) but a phone in a plane would probably add to the conjestion of data packets on a greater than normal quantity of towers. <<

So if you got a planeload of cell phones all going at once it could theoretically cause interference over major cities across the country one after the other as the plane travels cross-country. Another good reason not to allow use on airplane flights.

Thanks a lot!

Regards,
Melo
PL965 Spitfire pilot,
Glendale, CA

Hi Ben,

Thanks a lot! Just the kind of explanation I was looking for. It seems that one device would not be a problem, but a bunch of them in operation would lead to chaos.

Regards,
Melo
PL965 Spitfire pilot,
Glendale, CA

Hi,

The simple answer as was already discussed is that it is against the FAR's. The airlines don't have a choice. Many people think that the airlines made this rule to increase airphone usage. That is simply ridiculous. Most of rules passengers are subjected to are mandated by some government agency. Airlines are the most regulated industry in the U.S.
I'm an airline pilot, and it's often frustrating to hear passengers complaining about a rule as if it's our fault. We are in the middle.

Mark