> Is it?

Easy to test: add a SIM pin, turn on airplane mode and reboot your phone.

yes.

the sim has direct access to the radio and other modules, by design. it only needs the actual phone cpu/os for use interface.

if it wants to take the radio out of silent mode it can.

That seems like it wouldn't comply with FAA regulations.

I always presumed "airplane mode" was the specific set of features required by the FAA to enable the phone to do the same thing as a phone that's off, from the perspective of potential interference with a plane's communications.

If the SIM can still enable and use the radio despite "airplane mode" being on, then "airplane mode" is not really "a mode for making your phone safe to stay on while on an airplane."

It's actually an FCC regulation that prevents people using cellular devices on airplanes, and the issue isn't "interference with avionics" but "violating some fundamental assumptions that the existing cellular network is based on" like devices not travelling 600mph or having the ability to transmit signals for dozens of miles.

You can actually enable wifi yourself even while airplane mode is enabled - try it!

yes and that is not new.

try this: enable airplane mode and then open any app that has system permission to change gps or Bluetooth or wifi settings. it will enable those radio and the ui will still show the little airplane there.