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I know that passengers are asked to put their cell phones on flight mode. But some carriers allow use of WLAN on-board. So, what radios should passengers refrain from using? Also, if a person uses a GPS receiver on his/her mobile phone (on flight mode), would it interfere with the aircraft communication system?

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    $\begingroup$ Regarding GPS, it's a receiver $\endgroup$ – Simon Jun 20 '15 at 10:12
  • $\begingroup$ FAA now allows nearly everything but voice communication with cell phones, based on 220-page report which analyzed PED interferences and concluded that there are none. $\endgroup$ – mins Jun 20 '15 at 10:18
  • $\begingroup$ I've never understood this. A good buddy of mine is an avionics trainer for my local airline. He states, and pilots state, that they can often hear the cell negotiation from phones over the intercomm audio. I cannot grasp why official reports are concluding that there is no problem. $\endgroup$ – Simon Jun 20 '15 at 10:28
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    $\begingroup$ Pure GPS is receive-only, however most mobile communication devices that have it use a combination of various location-sensing techniques as the device's "location service" (cell towers, known WiFi hotspots) which are faster but less precise, and it's sometimes impossible to specify that you only want to use the pure GPS component. $\endgroup$ – KeithS Jun 22 '15 at 19:23
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    $\begingroup$ @PriyankGupta: The basic way to receive a GPS signal (or any other radio signal) is to extract the modulation from the modulated-carrier. This is usually done by an intermediate heterodyne operation which adds a RF signal to the signal received. This operation itself creates a RF signal of low power. This signal, or any of its by-products can create interferences to (badly designed) receivers. This is why we need to see all receivers as potential low power emitters until determined they are harmful. $\endgroup$ – mins Jun 24 '15 at 7:36
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There is actually a simple answer, but it probably isn't exactly what you are looking for: Refer all questions about what is allowed to your specific airline.

Each airline has to come up with their own list of allowable electronic devices, and submit that list to the FAA with appropriate documentation in order to gain approval to allow passengers to use them during flight.

Some airlines allow almost everything as long as it can be put into a non transmitting mode (airplane mode), while some still require ALL electronic devices to be completely powered down at all points during the flight.

Because of this, every airline is a little different and you are required to follow their rules while on their flights.

The GPS receiver would not cause problems, but this doesn't mean that you are necessarily allowed to use it, and there are other things in your phone that could cause a problem though.

In general, no electronic device that has a transmit function may be used because of possible interference though, unless specifically approved.

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  • $\begingroup$ Actually I wanted more technical answer. Also, for example, multiple airlines are ordering A320s from Airbus. Now what sense would it make to have different rules for the same A320s that are being sourced from the same company, i.e, Airbus. Moreover, I think Airbus/Boeing should decide what gadgets should be allowed on-board, since they know the best about their aircrafts. If you would, please tell me what other things in a phone can cause problems. $\endgroup$ – pri Jun 20 '15 at 15:47
  • $\begingroup$ While that would make sense, that is not how the rules are written, and each airline does indeed have their own policies which must be individually approved by the FAA and the manufacturer is not involved. The transmitters in a cell phone are what they are concerned about and why it should be put into airplane mode or turned off, depending on airline policy. $\endgroup$ – Lnafziger Jun 21 '15 at 10:43
  • $\begingroup$ @pri Actually, equipment configurations and flight procedures for specific aircraft models vary from airline to airline, and the airline chooses who does maintenance and upgrades, both of which may be done by companies other than the original aircraft manufacturer. Thus the airlines themselves are the authority on this. There may also be non-technical reasons for prohibiting specific uses of personal devices, such as not wanting phone conversations to inconvenience other passengers, or having hard objects that could be damaged able to fly about the cabin at certain points in the flight. $\endgroup$ – Curt J. Sampson Jul 31 at 6:27
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The simplest answer to your question is, none that have not been specifically approved for use by the FAA. The FAA, in U.S.-controlled airspace, has pretty much all the power and responsibility for ensuring civilian air travel is safe, and they operate with an abundance of caution in all things, because that draconian code of rules and regulations is what keeps the agency itself from taking blame for a plane crash; if everyone followed all the rules and the plane still went down, it's the government's butt on the line.

So, the FAA has, for decades, maintained more or less a blanket ban on operation of devices with a transmit feature, even as modern airframes (and by "modern" I mean practically anything in the sky today) are well-shielded against radio interference, and consumer devices available for purchase and casual use do not transmit on frequencies anywhere near those used by aircraft for communication or navigation. The reason is simply that it is possible for a device to cause interference with aircraft systems, whether directly by pirating the frequency or indirectly through intermodulation or other artifacts of radio carrier wave dynamics, and it was simpler, easier and cheaper at the time for the FAA to ban them all than to evaluate every device or device type against every airframe in commercial aviation, verify empirically that it does not cause interference, and educate flight crews and the general public about which device types, makes and models specifically are or are not allowed.

The FAA has since changed tack; it has worked with the FCC beginning in the 90s to develop a set of joint rules for both device and aircraft systems design that, if complied with by the manufacturers, will guarantee the device will not cause interference. Devices meeting these criteria, including practically any smartphone or tablet on the market today, can be used during "non-critical" stages of flight (all usage of potentially-interfering devices is still restricted during takeoff, landing or at any time by instruction of the flight crew) while onboard an aircraft certified for use of such devices while airborne (meaning the airframe complies with rules for shielding/isolation of sensitive electronics; this certification, including any needed retrofits, can be done during scheduled maintenance on each airframe).

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@PriyankGupta was heading in the right direction. Back when more people carried portable FM/AM receivers to listen to music, there was a problem with the receiver local oscillators causing interference. For example, If I wanted to listen to an FM station at 105.1 MHz, the local oscillator was 10.7 MHz above that frequencies so it was operating at 115.8 MHz. Leakage from the local oscillator could and did interfere with the aircraft receivers operating in that band. Of course, now days, almost no one uses portable FM broadcast receivers. However, the concept is the same for the various types of receivers and transmitters. The radios themselves may not interfere directly but one of the signals that gets mixed with another signal might. In modern commercial aircraft, they have multiple different systems so the likelihood of an airplane being severely compromised by a cell phone in the passenger section is very small but not zero. I always turn mine to airplane mode. I don't my family reading in the newspaper that the cause of a plane crash I was killed on was my cellphone being on.

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