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It's supposed to be that electronic gadgets' emission are dangerous for airplane systems. If this is true, why don't they use any detectors to locate such emissions?

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    $\begingroup$ This is an interesting point. Where I work they actually have devices to find hotspots that might be broadcasting our intranet. They're pretty accurate, and quite cheap. Not sure why airlines don't use them. $\endgroup$ – Jay Carr May 9 '14 at 17:57
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    $\begingroup$ They do, but the detectors are electronic devices and must be turned off at that time :) $\endgroup$ – TypeIA May 9 '14 at 17:59
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    $\begingroup$ Note that personal electronics are no longer banned by the FAA, and many airlines are also changing their policy to allow them at any point in the flight. The FCC still has regulations against using cellular signals from the air, although the chances of getting a signal from cruising altitude is roughly zero anyway. $\endgroup$ – Bret Copeland May 9 '14 at 18:36
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    $\begingroup$ Who claims that they are dangerous for airplane systems? $\endgroup$ – user2168 May 13 '14 at 14:38
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    $\begingroup$ @reirab: If you need a super complex device to intentionally pick up the signal, how comes the airplane itself accidentally picks up that signal and then gets influenced by it? $\endgroup$ – MSalters May 13 '14 at 22:38
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Three reasons I can think of:

  1. It's easy to detect the general presence of a specific transmitting device (a WiFi antenna, say), but very hard to precisely localize it. They could tell if there's one on the plane, but someone with a very sensitive piece of equipment would have to walk up and down the aisles pointing it at people to actually find it in somebody's pocket. And cellphones (when not in use) are generally burst transmitters: they don't broadcast continuously, they just "ping" the tower every so often. This means it could take a long time and a lot of aisle-pacing.

  2. Many "electronic devices" which are banned are entirely passive and have no traceable[*] emissions. Think cameras, handheld GPS receivers, iPods. (On the other hand this passiveness also means they are extremely unlikely to harmfully interfere with the operation of the airplane, but right or wrong, such devices are still banned in some cases.)

  3. It's not that important. There are a few incidents where electronic interference is suspected as a possible factor, but no conclusive evidence. As soon as there is actually a fatal accident where an electronic device can be conclusively blamed as the cause (and I doubt this will happen), the airlines will be a lot more willing to spend the kind of money that would be required to implement this.

For a full, evidence-based discussion of the actual risks, I refer you to this question on Skeptics Stack Exchange: Are personal electronics a risk to commercial aviation?

[*] No traceable emissions. All electronic devices generate some very, very tiny incidental signals. But these are so weak that they will be virtually impossible to detect on a crowded plane filled with its own (approved) electronics. Such emissions are measured in laboratories with extremely sensitive antennas in special, heavily-shielded rooms under carefully controlled conditions.

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  • $\begingroup$ 1. just don't let the plain to take off until the gadget is turned off 2. Why they are banned, then? $\endgroup$ – user626528 May 9 '14 at 18:12
  • $\begingroup$ @user626528 There's always going to be that one guy who refuses to turn his phone off (or isn't aware that it's on). Are you going to cancel the flight for this? What if someone leaves a phone turned on in their checked luggage? Pull all the bags off the plane and search them? What if it's one of the ground crew? As for why they're banned, there are a lot of reasons. FCC bans them to reduce the chance of disrupting the cell network on the ground. Flight attendants want them banned so that passengers will pay attention and not be obnoxious. This could make a full independent question. $\endgroup$ – TypeIA May 9 '14 at 18:17
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    $\begingroup$ @user626528 There are also some "Related" questions over on the right-hand side that discuss more about "why they're banned." $\endgroup$ – TypeIA May 9 '14 at 18:21
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    $\begingroup$ If turning off electronic devices has any importance - yes, it's better to cancel the flight. And if it's not important at all - well, just stop this stupid cargo cult theater. $\endgroup$ – user626528 May 9 '14 at 18:27
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    $\begingroup$ @user626528: you can think of the situation (before the recent lifting of restrictions) as this: if the occasional flight has a device or three left on, then there is an absolutely minuscule (tolerable) risk of a consequent accident. However, if every flight had dozens or hundreds of devices switched on, then there is a small (intolerably high) risk of a consequent accident. So asking passengers to turn off devices was sufficient since almost all co-operate. As evidence accumulated, the latter small risk has been re-assessed as minuscule. $\endgroup$ – Steve Jessop Jun 5 '14 at 19:09
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One thing to point out, electronics on planes really isn't as big of a safety factor as the airline would have you believe, and it's becoming less and less of an issue since consumer demands are pointing towards the aircraft that allow them to be entertained while traveling, such as have WiFi.

For the companies that run the phone lines it's a different story entirely. If your careening through the air at 500 knots and you make a phone call, you require the phone towers to do a lot more work receiving your call. I'm not sure why, but I remember reading that the main movement behind not using electronics while flying was really because our telephone infrastructure isn't capable of handling the excess load.

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  • $\begingroup$ You have some good points with the cellular network having difficulties: one is your effective range at an elevation of 30,000ft MSL (hint: quite good!), and the other is, you're moving so fast even if you did ping a tower, you'll be moving into a new cell anyway. Having it on wouldn't do a bit of good for you, so might as well use airplane mode. :) $\endgroup$ – dougk_ff7 May 14 '14 at 0:05
  • $\begingroup$ This applies only to cell phones. The reason for turning off all electronic devices in critical flight phases was indeed interference with the aircraft. At least in the U.S., that ban has been lifted. The ban on cell phones remains in the U.S. and is banned by the FCC due the fact that it used to wreak havoc on the cell network (in range of too many towers at once, handing off extremely frequently, etc.) $\endgroup$ – reirab Jan 9 '15 at 17:23
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Due to plentiful aircraft shielding and low power emissions of personal electronic devices, practically speaking only a malfunctioning electronic unit that is transmitting the exact same frequencies that the antennas are designed to receive and filter out carry significant probabilities of affecting avionics. One hundred iphones with wi-fi turned on would almost always have an effect, as they would not be emmiting signals received by the antennas. (If there was a rare malfunction a signal could pass from the cabin, through the window and into a GPS receiver, for example).

To identify the position of a malfunctioning unit one would need expensive multiple receivers and a computer that triangulates the location. This is just too expensive for the low risk.

Even if you could identify a malfunctioning unit, the unit would notmyet be malfunctioning otherwise the aircarft would already be receiving the bad signal and in a sense the aircaft systems are the first detection.

On the whole the answer lies in the fact that the interference for the odd electronic, people forget to turn off is low risk and does not justify the expense of an advanced locator system. It is the aircraft that provides the saftey by properly shielding its electronics from interfering signals to begin with. The antennas restrict communication on narrow frequencies amd usually with certain communication protocols, so even at the right frequency disturbing the aircarft instrumentation or navigation is a freak accident. I think the most probable interference is that a malfunctioning noise transmission across various uncontrolled frequencies could distort the coding a proper signal trying to communicate through the antenna to a given receiver.

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  • $\begingroup$ @dvnrrs - yes I understand that but in practical terms I do bot think the aircraft has much to worry about because of the shielding, except those frequency that actually pass through intended filters. I am speaking more from experience as I have written EMI/EMC tests for avionics installations. However I could be wrong as I have only heard second hand information of occurrences actually taken place in flight through this means.Anyway I should edit the first line to make it clearer. $\endgroup$ – esé May 13 '14 at 13:24
  • $\begingroup$ OK, I removed my downvote. However don't take this personally but I would still refer the interested reader to the thread on Skeptics which is thorough and heavily sourced using primary material. They don't have to "take either of our words for it." $\endgroup$ – TypeIA May 13 '14 at 13:38
  • $\begingroup$ @dvnrrs - interesting link and worth the read. thanks. $\endgroup$ – esé May 13 '14 at 14:15
  • $\begingroup$ The shielding from the aircraft itself can't protect against signals that are broadcasting on the same frequencies used by the avionics (i.e. signals like those you describe in your first sentence.) In order to do that, they'd block the signals they're trying to receive, too. $\endgroup$ – reirab Jan 9 '15 at 17:29
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The greatest danger appears to be when an aircraft is flying slowly, with landing gear open and there are cell towers on hills level with the approach path, because these are circumstances when a cell phone is most likely to make a call connection.

Many years ago working as an airline baggage handler in a country which prohibited all cell phone use during commercial flights, I was astonished to hear baggage carts with phones ringing all the time and it is the airport baggage halls where one could implement this policy or at the check-in counters. I imagine airlines would not be too keen on the extra manpower and wages required.

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  • $\begingroup$ The reason PEDs used to be banned during critical flight phases (taxi, takeoff, and landing) wasn't because that's when a phone is most likely to complete a connection, but because that's when accurate readings on the radionavigation equipment is most critical (especially final approach in low visibility conditions.) $\endgroup$ – reirab Jan 9 '15 at 17:32

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