Someone posted a thread on here a while back, complaining about how the Fenix 6 is useless because it can't track flights properly. As silly as that sounded to most of us, especially since it never even would have occurred to me to even try using the watch to track a flight, it got me thinking. So I made a copy of the "Track Me" activity, and called it "Track Flight", and then customized the datascreens. The results were great!
The watch couldn't get GPS lock at all in the first leg of my trip, a window seat in a 787. But to be fair, even my phone wasn't able to get a GPS lock in that plane, either... even on the tarmac. I think 787's just have way too much cabin isolation.
The second leg of my trip was in an Embraer regional jet, and the results were fantastic. Got a GPS lock right away, and worked perfectly all throughout the flight.
Anyways, here's how I configured my data screens - 2 pages, with the second page being the map. The first page shows distance (miles), timer, speed (miles per hour), GPS Elevation (the plane's actual elevation over sea level), Elevation (the altitude that the cabin is pressurized to), and GPS signal strength. It was a lot of fun watching how the cabin pressure altitude and actual altitude diverged during the flight. Watching the realtime ground speed during takeoff was fun, too.
Maybe this is due to a recent firmware update, but the watch had no problem with the extreme altitude or the extreme speed. I think previous reports said it cut out after 300mph? Mine showed 385mph just fine (which is as fast as the little jet went).