A CRJ-200 PILOT REPORTS ON HIS ACFT ROLLING BACKWARDS EVEN THOUGH THE PARKING BRAKE WAS SET. NOSE GEAR HAD ALSO TURNED FULL DEFLECTION TO THE RIGHT. NOSE GEAR WAS CHOCKED; BUT ONLY ONE TIRE.

Narrative

AFTER ARRIVING AT GATE; SET PARKING BRAKE; ENSURED BRAKE WAS ON VIA EICAS. NOSEWHEEL STEERING WAS OFF. AFTER PAX WERE UNLOADED; FO WENT INSIDE FOLLOWING WALKAROUND. CAPT AND FLT ATTENDANT WERE IN CABIN WHEN THE ACFT ROLLED BACKWARD. CAPT RUSHED TO COCKPIT TO FIND THE PARKING BRAKE HANDLE STILL IN THE ON AND LOCKED POS BUT NO EICAS INDICATION. TURNED ON HYD 3A BUT STILL NO EICAS. HAD TO TURN OFF BRAKE AND RESET HANDLE. UPON INSPECTION; FOUND THAT THE NOSE GEAR HAD TURNED FULL DEFLECTION TO THE R; DANGEROUSLY CLOSE TO THE TURN LIMIT MARKER. CONTACTED MAINT ABOUT POSSIBLE DAMAGE DUE TO EXCEEDING TURN LIMITS. MAINT TOLD CAPT THAT ANY DAMAGE AS A RESULT WOULD BE VERY OBVIOUS AND INSTRUCTED ON WHAT TO LOOK FOR. NO DAMAGE WAS OBSERVED BY CAPT OR LATER BY THE FO. HAD MAIN WHEELS CHOCKED AND NOSE CHOCK REMOVED FOR A FUNCTIONAL STEERING TEST. WHEN FO RETURNED; BRIEFED HIM ON WHAT HAD HAPPENED AND HAD HIM OBSERVE THE NOSE GEAR WHILE THE CAPT USED THE TILLER TO TAKE THE GEAR TO MAX DEFLECTION REPEATEDLY. FO NOTED NO DIFFERENCE IN SYMMETRY. ACFT WAS PARKED JUST PAST DEPRESSION POINTS IN THE ASPHALT CAUSED BY REPEATED PARKING OF ACFT ON SPOT. NOSE GEAR WAS CHOCKED BUT ONLY 1 TIRE. UNKNOWN TO MAINT OR CAPT WHY THE BRAKE CAME OFF. MAINT'S ONLY EXPLANATION IS THAT HYD PRESSURE BLED OFF; BUT CAPT FEELS IT WAS TOO SOON AFTER SHUTDOWN FOR THAT DEGREE OF BLEED-OFF TO OCCUR. WHATEVER THE REASON FOR THE BRAKE RELEASE; GRAVITY PULLED THE ACFT INTO THE DEPRESSIONS. THE CHOCK HELD BUT SINCE ONLY 1 TIRE WAS CHOCKED; THE NOSE GEAR TWISTED AROUND THE CHOCK TO THE FULL TURN LIMITS. RAMP SUPVR ARRIVED SHORTLY AFTER THE INCIDENT AND WAS VERY COOPERATIVE. INSTRUCTED ALL GND PERSONNEL THAT CHOCKS LONG ENOUGH TO COVER BOTH TIRES WERE TO BE USED. LOADING AND FUELING EQUIP WERE BEING USED AT THE TIME; BUT NO DAMAGE WAS OBSERVED BY CAPT AFTER INSPECTION TO ENSURE THAT GND EQUIP HAD NOT COME IN CONTACT WITH THE ACFT. CAPT HAS SINCE OBSERVED THE SINGLE CHOCK/SINGLE TIRE SCENARIO AT SEVERAL STATIONS. GND STATION NEEDS TO ENSURE THAT CHOCKS ARE USED ON BOTH NOSE TIRES.