I thought I read somewhere you do not necessarily need the internet. But when I tried starting up without connection, it wanted a DVD (which I don’t have).
Does anyone know if it’s even possible to play offline (other than disconnect from live traffic and not use multiplayer)?
Only if you have purchased the DVD version.
If you have downloaded the sim, as many people have, if your internet goes down you are completely screwed, as you cannot start the program.
Okay, thanks. I thought as much. I must say that in these days - at least for the well-connected - having no internet (apart from short outages) is also quite rare I suppose.
Revert to FSX then during internet-blackouts 
For what it’s worth the Game Pass version will work with no internet.
You cannot log on to game pass without the Internet.
Once you have logged on, you can defintely run the sim with no internet. I’ve tested this more than once.
But you cannot log on without the internet.
Didn’t you get the red connection warning? Or can you just click that one away and continue?
In my experience you only get the connection warning once the sim is running…and you cannot run the sim without logging on…which you cannot do without the internet.
Happy to be proved wrong
Disable your internet connection and try it. You will get a warning, but the sim will run.
Like I said above, I’ve tested this more than once.
Many thanks. I’ll give it a try.
No, you are correct. The sim cannot be started on a PC if there is NO Internet connection.
I powered down, unplugged from the internet, powered up, and tried to start the sim.
It asks for a DISK or Quit .
Thank you for that confirmation.
FWIW, there are already cracks and workarounds to this on the seedier side of the internet if one were so inclined to look.
Most of us would be so inclined… thanks !