PIC LEAVES AIRPLANE UNATTENDED WITHOUT REALIZING THE RT ENG IS RUNNING.

Narrative

UPON ARR AT DTW AND AFTER CLRING THE RWY 21R I ADVISED THE FO THAT BECAUSE WE WERE SO 'LIGHT;' I WAS HAVING TO CONSTANTLY APPLY THE BRAKES TO CTL TAXI SPD. WE WOULD BE SHUTTING DOWN THE R ENG. I OBSERVED THE AIR CONDITIONING PACK WAS SHUT DOWN AND I MOVED THE FUEL CUTOFF TOWARD THE OFF POS. THE L REVERSER LIGHT WAS STILL ILLUMINATED. BECAUSE OF THE EVER PRESENT CONSTRUCTION PROJECTS I SURVEYED THE TXWY FOR FOREIGN OBJECTS. SATISFIED THAT NO FOREIGN OBJECTS WERE PRESENT I BEGAN CYCLING THE REVERSER TO SOLVE THIS NEW PROB. THE LIGHT WENT OUT AFTER SEVERAL ATTEMPTS. THE FO INFORMED ME WE WOULD NEED THE APU AS THE GND PWR WAS RPTED INOP. I DIRECTED HIM TO START THE APU. IT WAS REACHING OP AS WE WERE ENTERING THE AREA ADJACENT TO THE CONCOURSE. APU OP APPEARED NORMAL BUT MY ATTN WAS FULLY ENGAGED ATTEMPTING TO ANALYZE THE MANEUVER REQUIRED TO PARK IN THIS HIGHLY CONGESTED AREA. THE PARKING MANEUVER WOULD REQUIRE MY WING TO PASS UNDER A DC10 WING AND MY WINGTIP APPEARED VERY CLOSE TO THE DC10 ENG NACELLE. THE LIGHTING IN THE GATE AREA WAS NOT VERY WELL FOCUSED AND SEEMED TO SHINE MOSTLY IN MY WINDSHIELD. I STOPPED THE ACFT AND DIMMED ALL MY FLT AND ENG PANEL LIGHTS TO AID IN OUTSIDE OBSERVATION. FINALLY ARRIVING AT THE GATE I SET THE BRAKES AND SHUT DOWN THE L ENG. AS WE WERE BEGINNING THE PARKING CHKLIST; THERE WAS A LOUD BANGING ON THE NOSE. THE AGENT WAS SIGNALLING THE EXTERNAL PWR WAS NOW AVAILABLE. I CHKED THE VOLTS/FREQ AND AFTER BEGINNING THE COOLING PROCESS ON THE APU I SELECTED THE EXTERNAL PWR SUPPLY. THERE WAS A MOMENTARY HESISTANCY FOR THE L BUSS TO ACCEPT PWR. I OBSERVED THAT BOTH THE L AND R BUSSES APPEARED POWERED. I THEN ATTEMPTED TO RECONFIRM THAT THE CHOCKS WERE IN. UNABLE TO ATTRACT AN AGENT'S ATTN I LEFT THE BRAKES SET AND CALLED FOR THE PARKING CHKLIST. WE WERE ON A TIGHT SCHEDULE AND ALREADY BEHIND DUE TO THE PROBS IN CLE. I DESIRED TO RETRIEVE THE FLT RELEASES ASAP AND AFTER THE LAST OF THE PAX DEPLANED I LEFT THE ACFT. THE FO FILLED OUT THE TIMES AND FUEL LOG. I LEFT THE JETWAY VIA THE EXTERIOR STAIRS; PROCEEDED TO OPS AND IMMEDIATELY RETURNED WHEN MY PREFLT DUTIES WERE COMPLETED. UPON MY RETURN I WAS ADVISED THAT I NEEDED TO GO TO THE TICKET PODIUM TO TALK TO 'THEM' ABOUT THE ENG RUNNING? I ASSUMED IT HAD SOMETHING TO DO WITH THE REVERSER UNLOCKED PROBS WE HAD EXPERIENCED. I DIDN'T FIND ANYONE IN PARTICULAR SO I RETURNED TO THE COCKPIT. I BEGAN PREFLT DUTIES AND A FEW MINS LATER THE MAINT SUPVR ARRIVED. HE SAT DOWN AND ASKED ME WHY I HAD LEFT THE ACFT WITH AN ENG RUNNING? I WAS FLABBERGASTED. I ASKED WHAT HE MEANT AND HE EXPLAINED TO ME THAT THE LINE MECH HAD SHUT DOWN THE R ENG. I WAS COMPLETELY DUMBFOUNDED. HOW COULD I HAVE COMMITTED SUCH EGREGIOUS TRANSGRESSION. I SPOKE WITH THE MAINT STAFF AND ASSURED THEM I WAS FULLY AWARE OF THE POTENTIAL FOR DISASTER. I CAN ONLY SURMISE THAT MY ATTN WAS SO DISTRACTED BY THE ONGOING EVENTS THAT THE R ENG WAS NOT SHUT DOWN ON TAXI IN. THE MECH WAS NOT SURE IF THE FUEL CTL WAS IN THE FULL ON POS OR PARTIALLY OFF. MY NORMAL CHKLIST ROUTINE WAS INTERRUPTED SEVERAL TIMES PARTICULARLY BY THE ATTEMPTS TO RECONFIRM THE CHOCKS WERE IN. I HAVE IN THE PAST EXPERIENCED ERRONEOUS CHOCK INDICATIONS. SO AT BUSY CONGESTED AREAS I OFTEN DOUBLE CHK THE CHOCKS. AS I WAS UNABLE TO RECONFIRM THE CHOCKS I LEFT THE BRAKES SET. HOWEVER I STILL DO NOT UNDERSTAND HOW I COULD HAVE PERCEIVED THE APU OR THE EXTERNAL ELECTRICAL PWR SYS POWERING THE R AC BUSS. THE R ENG GENERATOR SHOULD HAVE MAINTAINED PRIORITY. I DID NOT OBSERVE ANYTHING OUT OF THE ORDINARY IN REGARDS TO THE ELECTRICAL SYS OP.