RWY INCURSION BY ACR.

Narrative

AFTER TAXIING OFF THE RAMP AT BHM; THE CAPT DID NOT TURN ONTO TAXIWAY A; BUT CONTINUED TOWARD RWY 05/23 ON TAXIWAY E. GND CALLED US AND ASKED WHAT WE WERE DOING. THE CAPT STOPPED THE ACFT; STILL SHORT OF THE RWY ON TAXIWAY E. THE GND CTLR GAVE PERMISSION FOR A 180 DEG TURN ON THE TAXIWAY TO GO BACK TO TAXIWAY A. I (THE COPLT) TOLD GND THAT WE WOULD HAVE TO GO R A LITTLE BIT FIRST BEFORE MAKING THE L 180 DEG IN ORDER TO HAVE ENOUGH ROOM. GND SAID OKAY; AND THE CAPT PROCEEDED TO COME R IN PREPARATION FOR THE L 180 DEG. IN THE PROCESS OF COMING R; THE AIRPLANE ENTERED THE ACTIVE RWY. GND HASTILY CALLED AND ASKED WHY WE WERE PARTLY ON THE RWY. WE TOLD GND THAT WE HAD TO COME R A BIT BEFORE MAKING THE L 180 DEG; AND THAT HE HAD APPROVED IT. HE SAID (GND) THAT HE HAD NOT GIVEN PERMISSION FOR US TO BE ON THE RWY AND THOUGHT THAT WE WOULD 'SPIN IT AROUND' RIGHT WHERE WE WERE. THE COPLT INITIALLY THOUGHT THE CAPT WAS JUST GOING TO MAKE AN EXTRA WIDE TURN FROM THE RAMP ONTO 'A' AND WAS JUST ABOUT TO TELL THE CAPT WE WERE NOT CLRED FOR THE RWY WHEN GND INITIALLY CALLED. I (COPLT) SHOULD HAVE QUESTIONED THE CAPT SOONER SO AS TO PRECLUDE NEED FOR 180 DEG TURN. THE CAPT EXPLAINED THAT HE THOUGHT THE RWY (05/23) WAS TAXIWAY A AND THAT WAS WHY HE HAD CONTINUED ON 'E' TOWARD THE RWY. COPLT ALSO WILL ALWAYS LET GND KNOW IF AIRPLANE MIGHT IMPINGE ON A RWY BEFORE TAXIING IN SUCH A SITUATION.