Airborne use of GPS Watches

[A2QFI]

Apologies, I can't think of another thread on which to ask this question. I have bought a Seiko Ariston watch whose timekeeping is controlled and adjusted by the reception of time signals from GPS satellites. The watch instructions provide for the turning off of the reception mode, in an aircraft 'where the reception may influence the operation of other electronic devices in an aircraft.' Is this really a consideration? I find it hard to believe that a small GPS receiver could cause a problem, particularly as some airlines are considering allowing the use of mobile phones on board. Should I be turning this function off in flight?

[Oktas8]

GPS receivers are receivers, not transmitters. Therefore they cannot interfere with any other device.

"Flight mode", on devices equipped with it, are designed to switch off transmitters. But your watch has none in the first place! The only reason i can think of to switch off GPS would be to conserve power.

Most countries have lists of electronic devices that are permitted to operate at all times in flight. The lists include personal watches (and pacemakers, etc.)

So I would not worry about it. Use your watch anytime you like.

[A2QFI]

Thank you. The instruction book mentioned the facility but gave no reason for its existence. However, it may be a power conservation function, in that attempts to acquire satellites consume a great deal more power than merely running the watch time keeping. I do understand that the watch makes no transmissions.

[archae86]

Generally radio receivers make RF noise as a byproduct of their operation. While this is also true of just about any digital device, the details differ appreciably.

I'll not give advice on what this particular watch may transmit, but to say it does not transmit because it is a receiver is inaccurate.

I'm not a pilot, but am a retired electrical engineer.

Famously Peter Wright's Book Spycatcher recounts that UK intelligence flew aircraft over England in the 1950s specifically to detect the radio emissions from superheterodyne receivers then in use by Soviet spies. That particular byproduct noise was usefully detectable at considerable range.

[Uplinker]

Just to elaborate slightly, but still keeping it simple;

Basically any radio frequency receiver works by combining the received radio frequency from the aerial with the output of a "local oscillator". The result is a much lower frequency that can then be decoded by the circuitry.

This local oscillator output can be radiated 'backwards' through the aerial - it shouldn't be, but it can be, particularly by simpler, cheaper and smaller receivers which do not have the physical space for components called isolators which prevent this happening.

So, the point is, some receivers CAN and do radiate even though they're not supposed to.

This might be the reason for the restriction.

[Gauges and Dials]

GPS receivers are receivers, not transmitters. Therefore they cannot interfere with any other device.

As others have pointed out, radio receivers radiate some RF, typically at their intermediate frequency (IF).

But.... if you consider the size of the battery in your GPS watch, and how long the unit runs on that battery, it's pretty safe to assume that the amount of radiated power is miniscule.

[Metro man]

FM radios and portable TVs are banned from being used but they are just receivers as well.

[fizz57]

Given the accuracy of even cheap quartz oscillators and the limited energy budget of a wristwatch, I would suppose that the GPS receiver is only turned on for a short interval every few hours to synchronise the internal timekeeper. After all, a wristwatch is likely to be in several places (besides an airliner cockpit) where GPS reception is lacking, such as inside buildings or underground, as well as in street canyons, trains and buses where reception can be poor or intermittent.


On a related note, when flying (as SLF!) I often try to get a fix on my smartphone GPS, if only because I don't usually see those numbers on my TomTom. It is actually quite difficult to do so, and requires holding the phone close to the window for several minutes but also that there are a number of satellites at a low altitude on your side of the aircraft. After getting a fix by holding the phone close to the window, it usually manages to retain the fix even if placed say on the aisle seat table. Also it seems to be easier to get a fix on a Boeing than on an Airbus, but I believe there's another thread for that :)

http://i1380.photobucket.com/albums/ah174/lzamm1/a99211f1-4ea9-415f-8400-8bf985f67862_zpscdeacf5d.jpg

[No Fly Zone]

Like many, I've followed this for years. The well-read but non-professional take is that devices similar to your self/GPS setting watch are not relevant to the aircraft's systems; in short, it sucks signals when it can find them, computes a little bit and does not blow. I have personal knowledge of several long-haul pilots who use similar devices without issue. Thus, the best advice is to use it, forget about it and *perhaps* be prepared to turn it off if anyone ever asks. I have to see this as a non-issue.
My personal use? I carry a hand-held transceiver and headset, simply because I like to know what's going on. Obviously, I keep the Tx function locked-out when I'm a pax and tend to keep the radio out of sight save the several frequency changes necessary. The headset used as SLC does NOT even have a mic and my radio provides a no-trx switch that I use. Said switch is bump-proof and use of the trx-disabled unit does NOT violate any rules. It provides more detail than does United's Chnl 9 and more often. It is also a nice "Second View" of what is happening with ATC, even when the flight and cabin crews LIE a lot. I never challenge them, but take some comfort in hearing original broadscasts fro ATC and company operations. Sorry, but flight crews (and cabin crews) do NOT always tell the truth. So why do I bother? 1) with the Trx function locked out, I am no threat to anyone, 2) In monitor-only mode, I hear a lot more detail than anyone of the airplane will ever explain and some listening often saves me 10-15 minutes on the tereminal end. And - without the antenna or mic, the modest unit rarely attracts any attention; I just listen. And know.

[Gauges and Dials]

NoFlyZone, you're forgetting secondary emissions.

Just because something is "not a transmitter" doesn't mean that it emits no RF. That's why using your laptop is fine, but using an external mouse is banned -- because the mouse wire is not shielded, and emits a fair bit of RF.

Your VHF transceiver has an intermediate frequency oscillator. Depending upon the build quality, whether the case is metallic or plastic, and a number of other factors, it, when operating in RX mode with TX locked out, still emits some RF at the intermediate frequency. That's why the use of FM and TV radio receivers is banned on aircraft.

If the IF of your transceiver is the same as the IF of the aircraft's comm radios (which it is likely to be), then there's the very real possibility of interference.

Yes, the chance is slight, but, at the end of the day, the process by which "everything not specifically approved is banned." is intentionally conservative, which is pretty much the way you, as an occupant of the airplane, want it to be, no?