What is a functioning power turret?
The errata posted last year clarifies the definition of a power turret in rule 5.5.2.

Powered Turrets: Chin (B-17G), Nose (B-24J), Top
Turret and Ball Turret (All models of B17 and B24) and tail guns (B-24). The Tail Guns (B17) are
not powered.