Narrative:

Bil stations needed the gate that was occupied by our large transport and asked us to ride the brakes during towing to remote parking. The flight engineer and I took our respective seats with the APU on bus for electrical and a b-pump on for brake pressure. After reaching parking, the tug driver asked for brakes set via interphone. I set the brakes while electrical, b-sys and hydraulic brake pressure were available and normal. No ramp slope was noted. The flight engineer then ran the shutdown and termination checklists as the airplane was to situation for several hours awaiting slc mechanics to fix a bad start valve. I left the parking brake set and the APU was shut down. We then left the airplane via the aft stairs and walked to the front where we got in the tug for a return to the terminal. Not more than a few mins passed between shutdown and reaching the tug. When in the tug, the flight engineer noticed the airplane rolling backwards. I jumped from the tug and chased the airplane at a full run for about 10 seconds, re-entering through the aft stairs. Once in the cockpit, I turned on the battery and APU start switches and took my seat where I applied full braking with no response noted. The airplane ultimately rolled about 1000 ft and came to a stop off the paved surface. The APU did not reach operating speed until after the airplane stopped. I then put the APU generator on line, pressurized b-sys and re-set the parking brake. The airplane was towed back to its original stopping spot and I deplaned through the forward entry door on a belt loader. Supplemental information from acn 257425: temperature minus 1 degree F, txwys patchy snow/ice, winds 10 KTS. Contributing factors: unperceived slope of taxiway, bitter cold, less than desired maintenance support all morning. Causes: captain (crew) did not confirm 'chocks in' before depowering and exiting aircraft. Ground personnel disconnected aircraft from tug, knowing that chocks were not yet installed. Residual, accumulator brake pressure did not keep aircraft stopped on that slope. But that pressure did take at least 3 mins to dissipate. There was a significant (3-5 min time) between depowering aircraft and initial backward roll. An large transport nearby may have provided some jet blast. Solution: crew member at controls should confirm status of chocks or at least that tug will stay connected before leaving brakes unattended or unpowered. Other crew members should back this up. Ground personnel should not have disconnected tug without chocks installed.

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Original NASA ASRS Text

Title: LGT PARKED ON ICY TXWY SLIDES AFTER PARKED AND TUG DISCONNECTED.

Narrative: BIL STATIONS NEEDED THE GATE THAT WAS OCCUPIED BY OUR LGT AND ASKED US TO RIDE THE BRAKES DURING TOWING TO REMOTE PARKING. THE FE AND I TOOK OUR RESPECTIVE SEATS WITH THE APU ON BUS FOR ELECTRICAL AND A B-PUMP ON FOR BRAKE PRESSURE. AFTER REACHING PARKING, THE TUG DRIVER ASKED FOR BRAKES SET VIA INTERPHONE. I SET THE BRAKES WHILE ELECTRICAL, B-SYS AND HYD BRAKE PRESSURE WERE AVAILABLE AND NORMAL. NO RAMP SLOPE WAS NOTED. THE FE THEN RAN THE SHUTDOWN AND TERMINATION CHKLISTS AS THE AIRPLANE WAS TO SIT FOR SEVERAL HRS AWAITING SLC MECHS TO FIX A BAD START VALVE. I LEFT THE PARKING BRAKE SET AND THE APU WAS SHUT DOWN. WE THEN LEFT THE AIRPLANE VIA THE AFT STAIRS AND WALKED TO THE FRONT WHERE WE GOT IN THE TUG FOR A RETURN TO THE TERMINAL. NOT MORE THAN A FEW MINS PASSED BTWN SHUTDOWN AND REACHING THE TUG. WHEN IN THE TUG, THE FE NOTICED THE AIRPLANE ROLLING BACKWARDS. I JUMPED FROM THE TUG AND CHASED THE AIRPLANE AT A FULL RUN FOR ABOUT 10 SECONDS, RE-ENTERING THROUGH THE AFT STAIRS. ONCE IN THE COCKPIT, I TURNED ON THE BATTERY AND APU START SWITCHES AND TOOK MY SEAT WHERE I APPLIED FULL BRAKING WITH NO RESPONSE NOTED. THE AIRPLANE ULTIMATELY ROLLED ABOUT 1000 FT AND CAME TO A STOP OFF THE PAVED SURFACE. THE APU DID NOT REACH OPERATING SPD UNTIL AFTER THE AIRPLANE STOPPED. I THEN PUT THE APU GENERATOR ON LINE, PRESSURIZED B-SYS AND RE-SET THE PARKING BRAKE. THE AIRPLANE WAS TOWED BACK TO ITS ORIGINAL STOPPING SPOT AND I DEPLANED THROUGH THE FORWARD ENTRY DOOR ON A BELT LOADER. SUPPLEMENTAL INFORMATION FROM ACN 257425: TEMP MINUS 1 DEG F, TXWYS PATCHY SNOW/ICE, WINDS 10 KTS. CONTRIBUTING FACTORS: UNPERCEIVED SLOPE OF TXWY, BITTER COLD, LESS THAN DESIRED MAINT SUPPORT ALL MORNING. CAUSES: CAPT (CREW) DID NOT CONFIRM 'CHOCKS IN' BEFORE DEPOWERING AND EXITING ACFT. GND PERSONNEL DISCONNECTED ACFT FROM TUG, KNOWING THAT CHOCKS WERE NOT YET INSTALLED. RESIDUAL, ACCUMULATOR BRAKE PRESSURE DID NOT KEEP ACFT STOPPED ON THAT SLOPE. BUT THAT PRESSURE DID TAKE AT LEAST 3 MINS TO DISSIPATE. THERE WAS A SIGNIFICANT (3-5 MIN TIME) BTWN DEPOWERING ACFT AND INITIAL BACKWARD ROLL. AN LGT NEARBY MAY HAVE PROVIDED SOME JET BLAST. SOLUTION: CREW MEMBER AT CTLS SHOULD CONFIRM STATUS OF CHOCKS OR AT LEAST THAT TUG WILL STAY CONNECTED BEFORE LEAVING BRAKES UNATTENDED OR UNPOWERED. OTHER CREW MEMBERS SHOULD BACK THIS UP. GND PERSONNEL SHOULD NOT HAVE DISCONNECTED TUG WITHOUT CHOCKS INSTALLED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.