I thought I'd put this up right now, since the rules are not really clear in the current version of the game's manual:
Banking is not restricted to 1 hex - you can bank as many hexes to either side as your ship's Turn Rate allows. This would allow for a maximum of up to 3 hexes, but since you have to move half of your speed in hexes before banking, and banking 1 hex eats up 1 movement point, you can bank 2 hexes at the most when NOT using your afterburners. (Fighters with a Turn Rate of 3 can bank 3 hexes when running on afterburners.)
Banking is not restricted to 1 hex - you can bank as many hexes to either side as your ship's Turn Rate allows. This would allow for a maximum of up to 3 hexes, but since you have to move half of your speed in hexes before banking, and banking 1 hex eats up 1 movement point, you can bank 2 hexes at the most when NOT using your afterburners. (Fighters with a Turn Rate of 3 can bank 3 hexes when running on afterburners.)