I have no idea about the mandatory part. However, IMO those who want to survive a confrontation are armed with a .44 mimimum.
I would not want to have to use only the .44 against an Alaskan Brown who's focused on my destruction.
As pictures on this thread show, the Grizzly is a BIG bear and very hard to stop. Best advice is stay away from them, especially on their turf.
It's mandatory by state law that aviators carry a survival kit that includes a firearm in all aircraft, private and charter. The type of firearm is very reasonably not specified, and though most Alaskan pilots have a pretty good idea of what to do with a hunting rifle and have a preferred choice of one, the space restrictions make handguns and shorty shotguns particularly popular. But even a .22 rimfire satisfies the legal requirement.