[imoverclocked]

It was never about that. It’s about interference with aircraft systems.

Look for “5G NOTAM” if you are someone who thinks this is bunk. Specifically, some radio altimeters (which are needed for some IMC approaches) can be interfered with by the adjacent 5G frequency bands due to not being built with a tight enough filter.

[stephen_g]

The 5G issue was more about flying in or over anywhere that had a 5G service using that particular band - it didn’t matter whether anyone on the phone did or did not have a phone on.

Hence the whole US aircraft fleet was upgraded (by the end of September 2023) so that band could be used for 5G there and it’s no longer a problem.

As I understand it, cellular modems wouldn’t transmit on a frequency if they can’t see a base station (tower) first on that channel, so I expect before the problem was fixed, the temporary solution was just to disable that band at the base stations.

If there was any actual known or suspected risk of electromagnetic compatibility issues with any consumer devices, there would be very strict laws about it (it might become a Federal offence not to have your phone in airplane mode, for example - but obviously it’s not)

[imoverclocked]

We can further caveat that it wasn't "anywhere that had a 5G service" since the radio altimeter is not needed except on low visibility approaches into an airport.

Either way, it's about interference with aircraft systems from cellular infrastructure/devices. Certainly, if a tower talking on 5G can interfere with a radio altimeter, a bunch of cellphones onboard could do the same thing or even amplify the effect.

> it might become a Federal offence not to have your phone in airplane mode, for example - but obviously it’s not

Violating directions from the flight crew can be a federal offense. There is a chain of authority from the FAA to the airlines and to the PIC. The airline and PIC delegate part of that authority to the rest of the crew. Unless you are very aware of every regulation and particular company policy, I highly recommend that you don't test this.