Misleading iOS Time Updates

I have a truly love-and-hate relationship with my Garmin watch. I love it for the looks. And for keeping record of my daily trail runs. And for holding backup topographic maps of (almost) the entire planet. And for being the flight computer on long distance flights.

Actually the last part is also a contributor to the hate part. As it keeps the location track in flight through combined satellite readings, it also updates its time to the GPS time. And a time zone with it - meaning it always shows accurate time for the current location. Which is useless when you are just a passenger. You wake up in the night, look at the watch - it shows time, but at a glance you just don't have an idea in which time zone you are in. Yes, there is always 1pm somewhere on Earth.

But generally when flying, the best way is to have either the departure time zone or the arrival time zone, not something in between. A phone use to be then a much more convenient time source - just showing the departure time zone time until the flight mode was disabled at touchdown. But it turns out a phone is not a reliable time keeper either...

Two weeks ago when returning from New Zealand, on a BKK-IST flight, as usual I put my iPhone in a flight mode before the take off. After several hours during which I had a great dinner and a good doze of sleep, I realized something was way off. The time on the phone was neither the departure nor the arrival time zone. It was something in-between. To be precise 90 minutes behind the Bangkok time.

Yes we were flying over India and to my vague recollection the Indian time zone was shifted by a fraction of an hour, not a full hour. Things matched. The phone clearly adjusted its time zone to the Indian time. But how and why? It was in the flight mode and I was sitting in the middle row seat, far from any window.

To be honest - I'm still not sure what / how it happened.

One theory is it tried connecting to the onboard WiFi and got the update this way, but still, doesn't the onboard WiFi carry the time of a fixed ground station? Or did the plane's MAC address geolocation got somehow updated on the way? Automatically or because another passenger with a GPS signal was using the WiFi? The phone was in a flight mode, but these days switching WiFi or Bluetooth off still does not work as a hard switch - the radios wake up from time to time to do some "Apple" stuff.

Another theory is the phone really somehow picked up the satellite signal and updated its location and that update resulted in the system shifting the time zone.

In any case, after consulting Gemini, it says, write a script that disables automatic time zone updates when you switch to flight mode. Actually this - I think - is what the iOS should really be doing. But these devices live lives of their own these days...