SOS Mode

Same reason as above. If you lose signal for several minutes (in a large city skyscraper a long elevator ride can trigger it) it will shut down the cellular radio to conserve power. Turning airplane mode on for 15-30 seconds, then turning it off restarts the cellular radio.

This just happened to me twice on a recent trip. At the beginning of the flight, I did not switch my phone to airplane mode. Later, when I grabbed my phone to use it, it said SOS. Absolutely nothing I could do would fix it. I even powered down my iPhone and back up, and it still said SOS. I tried switching it to airplane mode and back, and the SOS was gone. Three flights later, on one of my return legs, I again forgot to switch to airplane mode, and again the phone said SOS. This time I knew exactly what to do. I switched it to airplane mode, and when I switched back, the SOS was gone. Is it possible my iPhone was being forced into SOS mode because I didn't switch to airplane mode?

And for some reason you lost cellular signal for a few minutes. Either a local network outage, an overloaded tower that couldn’t respond to your phone’s “ping” or a very week cellular signal. Do you have Wi-Fi Calling enabled? It can prevent network outages from affecting your phone if you have a strong Wi-Fi signal.

The other possibility is an intermittent hardware problem in your phone.

Indirectly because you didn’t switch to airplane mode. When the phone loses signal it tries to re-acquire signal for several minutes. If it fails after trying for a while, it stops trying, essentially putting the phone into a state similar to airplane mode. So it’s not really a big deal if you forget to put it into airplane mode when flying; it will stop trying for a cellular connection, which is almost the same thing.

Mine just did this. I tried restarting my phone twice, turned Wi-Fi & cellular both off & on. Nothing worked. Just popped back on after a few minutes.

I wasn’t flying when it happened to me. Same phone.

I was sitting in the second floor of my house.

I keep seeing stuff about promax 13s doing this. Never had this problem before.