ACFT DAMAGED WHEN ACFT MOVES BACK FROM GATE AND IMPACTS ON FUEL TRUCK.

Narrative

ON A SINGLE ENG TAXI TO GATE AT DETROIT; DURING PARKING; IT TOOK 3-4 PWR APPLICATIONS TO GET ON TO THE SIGNALMAN'S MARK. THE LAST FEW FT WERE ON AN INCLINE TO GATE. AS I CAN BEST RECALL; I SET THE BRAKES AND RECEIVED A CHOCKS- IN SIGNAL. AFTER THE PARKING CHKLIST WAS COMPLETED; AND UPON MOVING MY SEAT BACK TO FILL OUT THE ACFT LOGBOOK; THE BRAKES ACCIDENTALLY DISENGAGED. BECAUSE OF THE LACK OF VISUAL CUES; DARKNESS AND POOR ILLUMINATION; I WAS NOT AWARE THE ACFT HAD STARTED ROLLING BACKWARDS; DOWN THE SLOPE AT GATE. APPARENTLY; THE CHOCKS HAD SLIPPED ON THE SLICK RAMP; OR DUE TO THE INCLINE THE ACFT JUMPED THE CHOCKS. THEREFORE; R WING AILERON ASSEMBLY IMPACTED A FUEL TRUCK BEHIND THE WING. THE PAX SVC AGENTS WERE MOTIONING; AND I NOTICED THEY WERE MOTIONING AND THEN REALIZED WE HAD MOVED BACKWARDS APPROX 6 FT. I MOVED MY SEAT FORWARD AND PHYSICALLY HELD THE BRAKES; AND OPENED MY SLIDING WINDOW TO ASK IF ANYONE WAS HURT. THE EXTERNAL PWR HAD BEEN CONNECTED BUT WAS LOOSE SO THE FO STARTED THE APU. THE FIRST INDICATION I HAD THAT THE ACFT HAD STRUCK SOMETHING WAS WHEN A MECH GOT ON THE INTERPHONE AND TOLD US. APPARENTLY THE FO HAD FELT A SLIGHT BUMP ON THE YOKE WHEN THE AILERON WAS STRUCK. I REMEMBER ASKING THE MECH IF EVERYONE ON THE RAMP WAS OK; OR IF THERE HAD BEEN ANY FUEL SPILLED; BUT THE MECH EITHER DID NOT HEAR OR WAS OFF INTERPHONE. I THEN ASKED THE FO TO GO TO THE RAMP TO ACCESS THE SITUATION. WHEN THE MECH CAME BACK; A FEW MOMENTS LATER; HE SAID HE PLANNED ON JACKING UP THE R STRUT; AND FREEING THE ACFT FROM THE FUEL TRUCK; TO LIMIT THE DAMAGE TO THE AIRPLANE. BY THIS TIME THE AGENTS WERE DEPLANING PAXS DOWN THE REAR STAIRS. I MADE A LOGBOOK ENTRY; AND RELEASED THE CREW AFTER ALL THE PAXS HAD DEPLANED. I THINK THE GND CREW WERE POSSIBLY PUT OFF GUARD ALSO BY THE PWR AND ATTEMPTS TO GET THE ACFT TO THE GATE. I FEEL VERY BADLY THAT THE INCIDENT OCCURRED; BUT AM GRATIFIED THAT THERE WERE NO INJURIES. AS THE CAPT I FEEL I AM RESPONSIBLE; BUT SOME CIRCUMSTANCES LIKE THE SLOPE; SLIPPERY RAMP; AND THE CHOCKS NOT HOLDING WERE BEYOND WHAT I CTL.