@rforelli
From the “Air Base”-unit characteristics, Rulebook Pacific 1940.2, page 25:
Increased Air Unit Range: When taking off from a friendly territory that has an operative air base, air units gain 1 additional point of movement range. At that point fighters and tactical bombers can move 5 spaces, and strategic bombers can move 7spaces. Note: Air units on carriers in a sea zone adjacent to a territory containing an air base don’t benefit from this additional movement range.