I think that my question is pretty self-explanatory. I‘m interested in both general-aviation and commercial jet pilots.
4 Answers
Almost always.
If they don't, you often end up with this annoying sound on the radio:
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1$\begingroup$ Ahh, I‘ve encountered such a sound in my FM car radio before. Thanks a lot! $\endgroup$ Commented Nov 21, 2019 at 10:26
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6$\begingroup$ I think it's worth noting that this GSM buzz is characteristic for the TDMA modulation that is used in GSM (2G) phones. 3G (UMTS) and 4G (LTE) standard phones modulate in CDMA or OFDMA, provided that the base station allows 3G or 4G. These modulations cause much less audible interference. 10 years ago, I heard GSM buzz on daily basis in teleconferences. These days, the sound has become pretty rare. Nevertheless, the absence of audible buzz doesn't mean that there is no interference - possibly impacting your navigation receivers. $\endgroup$– boglCommented Nov 21, 2019 at 13:20
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3$\begingroup$ Based on my non-scientific observations of GA pilots in the US, I'd say "almost never". It's very common for pilots here to use their cell phones for getting clearances, texting en route, checking weather, activating flight plans and so on. That's not to say it's always legal or advisable, but it's very, very common. Personally, I just forget to put it in airplane mode most of the time. $\endgroup$– PondlifeCommented Nov 21, 2019 at 16:52
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1$\begingroup$ @Pondlife What clearances would a pilot get in-flight via cell phone? I wouldn't say it's "very common", I've never heard of any pilot, locally at least, that got a clearance or activated a flight plan via phone (in the air). All those services are easily available via FSS. $\endgroup$ Commented Nov 21, 2019 at 18:41
it depends on the flight. With a low altitude lower speed ( <200kts) GA flights they can still be useful and can serve as a usefull backup. Once you travel faster than 200 kts, and higher than about 12,000 you end up switching cell towers too fast and the phone uses a lot of power trying to get as strong enough signal. If connected to the planes power this will increase the possibility of the phone creating radio interference (analog audio or nav signals)
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2$\begingroup$ I fly part time for a small part 135 operator. Always below 10K' and <200 KIAS. We have verified that there are no interference issues, and let passengers know that it is OK to keep them on. $\endgroup$ Commented Nov 21, 2019 at 18:02
The item "Mobile phone ... OFF" is (or at least was) actually a part of the Before Engine Start checklist on several commercial aircraft types. I tried to come up with a reference, but most photos found online only refer to PC simulator software. However, there seems to be one actual photo of the checklists on the cockpit table from a real A320 aircraft found here.
Personally I have seen Airbus (A320/A330/A340) pilots of at least one major European carrier going through that checklist item and accordingly checking and verbally confirming that both their mobile phones were switched off.
(Disclaimer: this experience was 10+ years ago. I don't know whether policies have changed since.)
I am a novice, non-professional pilot. I have never seen anyone (instructors, examiners, other pilots) switch their phone to airplane mode, and in fact it is not uncommon to make cell phone calls from the air. It is also extremely common to use data connected applications (e.g. ForeFlight) from the air.
That being said, it seems like a pretty good idea to keep it in airplane mode when you aren't using it, especially when not navigating visually. As mentioned in some other answers, cellphones definitely can cause radio interference.