UNAUTHORIZED RWY ENTRY BY ACR.

Narrative

AFTER ROUTINE PUSHBACK AND START; FLT WAS CLRED TO TAXI TO RWY 15R. NO SPECIFIC TAXI (RTING) INSTRUCTIONS WERE PROVIDED. TAXI OP COMMENCED FROM AREA OF PIER E AND; R TURN WAS MADE ONTO TAXIWAY A; SEBOUND. THIS CAPT HAD NOT OPERATED IN OR OUT OF BWI FOR AT LEAST 2 YRS. FO ALSO HAD MADE ONLY INFREQUENT FLTS AT THIS ARPT. APCHING RWY 4/22 ON 'A' I MISTOOK THE RWY FOR THE OUTER 'O'; WHICH LOOKED LIKE A GOOD CLR RTING TO TAKE TOWARDS 15R. VERY SOON AFTER WE LINED UP SEBOUND ON RWY 4/22; I DISCOVERED THE ERROR (NOTING WHITE RWY LIGHTS) AND INSTRUCTED MY FO (COPLT) TO TELL BWI GND CTL WE HAD MADE AN ERROR AND WERE ON A RWY. WITH NO PARTICULAR CONCERN BEING EXPRESSED; THE CTLR INSTRUCTED OUR FLT TO TURN R AT C; L ONTO THE OUTER AND CONTINUE TO 15R. FORTUNATELY; RWY 4/22 WAS NOT IN USE AS AN ACTIVE RWY AT THIS TIME. APPARENTLY THERE WAS NO CONFLICT WITH OTHER TFC -- ON GND OR IN THE AIR. MY FO WAS 'HEADS UP' DURING THIS INCURSION AND DIDN'T REALIZE THE ERROR -- THAT WE HAD ENTERED A RWY WITHOUT SPECIFIC CLRNC. CHARTS DEPICTING THE ARPT LAYOUT WERE STUDIED BEFORE TAXI OP COMMENCED. THE LACK OF OBVIOUS SIGNS OR LIGHTS MARKING THE TRANSITION FROM THE VERY WIDE TAXIWAY A TO RWY 4/22 WAS A CONTRIBUTING FACTOR; AND WAS MY LACK OF FAMILIARITY WITH BWI'S LAYOUT AND NEAR DARKNESS OF THE HR. I SHOULD HAVE REQUESTED SOME HAND-HOLDING FROM BWI GND CTL; TURN-BY-TURN DIRECTIONS TO 15R. ATC OFTEN ASSUMES ALL ACR PLTS ARE FAMILIAR WITH ALL ARPTS. IF USE OF THE RWY 4/22 WAS OK FOR TAXIING TO 15R; ATC SHOULD HAVE SPECIFICALLY APPROVED ITS USE. IT IS TOO EASY; AT TOO MANY ARPTS; TO INADVERTENTLY BLUNDER ONTO RWYS -- ESPECIALLY ACTIVE ONES. LIGHTING AND PAINTED MARKINGS NEED TO BE ENHANCED/IMPROVED AT MANY ARPTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN STRUCTURED CALLBACK FOR RWY INCURSION STUDY. THERE IS VERY WIDE PAVED AREA WHERE TAXIWAY A MEETS RWY 22; AND IF ACFT IS NOT NEAR EDGE OF THIS PAVED AREA THE FLC COULD NOT SEE ANY RWY DESIGNATION SIGNS. THIS FLC DID NOT REALIZE THEY WERE APCHING A RWY. SAYS TWR CTLR DID NOT SEEM TO CARE IF THEY TAXIED ON RWY 22 RATHER THAN ON TAXIWAY O. DID NOT SEE ANY OTHER TFC; AND TWR DID NOT MENTION ANY TFC INVOLVED. RPTR HAD NOT FLOWN WITH THAT FO BEFORE. RPTR HAD COMMUTED FROM LONG ISLAND TO ORIGINATE FLT AT BWI. HAS NOT BEEN INTO BWI SINCE INCIDENT.