Narrative:

We were cleared to pushback in sjo. Prior to pushback, we conducted an alternate brake check as per maintenance release document (mrd) due to a deferred bscu #1 problem. At the completion of pushback, I set the parking brake and the mechanic disconnected the tow tractor. The airplane then began to roll backwards. I repeatedly pressed the brake pedals and cycled the parking brake handle but the airplane would not stop. My first officer cycled the anti-skid and nosewheel steering switch, also with no effect. We then commenced engine start to obtain hydraulic pressure and forward thrust. At the same time my first officer transmitted to ground control that we had lost our brakes, and directed the flight attendants to be immediately seated. As the #1 engine spooled up I again released the parking brake and used the brake pedals to stop the airplane safely on the taxiway. No one was injured and no damage occurred. We then had the mechanic hook the tow tractor back up to our aircraft and tow us back to the gate. At the gate the mechanic explained that the brake accumulator had probably been partially depleted during the overnight stay and the additional maintenance release document alternate brake check had further depleted the accumulator to the point the brakes would not hold the airplane in place on the sloped taxiway. After charging the brake accumulator with the yellow hydraulic system, we accomplished another alternate brake check, again recharged the accumulator, restarted the #1 engine at the gate, and commenced an uneventful pushback. The A320 flight handbook contains no emergency procedure or irregular procedure for brake failure. It does contain a warning to release the parking brake in the event the airplane starts moving during engine start, but does not address the starting of the yellow hydraulic system electric pump to gain immediate hydraulic pressure. The maintenance release document procedure for the alternate brake check does not contain a step to recharge the brake accumulator after performing the check. 1) add A320 loss of brakes emergency procedure to include: a) parking brake -- release. B) yellow hydraulic system electric pump -- on. 2) add new step to end of A320 maintenance release document alternate brake check: recharge brake accumulator with yellow hydraulic system electric pump. Callback conversation with reporter revealed the following information: the reporter stated he required check for the deferred item depleted the yellow system accumulator and was not replenished with the yellow electric hydraulic pump. The APU was running and #1 engine was started and supplied hydraulic pressure for the normal braking system.

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Original NASA ASRS Text

Title: AN AIRBUS A320 AFTER PUSHBACK AND TOWBAR DISCONNECT THE ACFT ROLLED UNCTLED BACKWARDS WITH NORMAL BRAKE SYS INEFFECTIVE.

Narrative: WE WERE CLRED TO PUSHBACK IN SJO. PRIOR TO PUSHBACK, WE CONDUCTED AN ALTERNATE BRAKE CHK AS PER MAINT RELEASE DOCUMENT (MRD) DUE TO A DEFERRED BSCU #1 PROB. AT THE COMPLETION OF PUSHBACK, I SET THE PARKING BRAKE AND THE MECH DISCONNECTED THE TOW TRACTOR. THE AIRPLANE THEN BEGAN TO ROLL BACKWARDS. I REPEATEDLY PRESSED THE BRAKE PEDALS AND CYCLED THE PARKING BRAKE HANDLE BUT THE AIRPLANE WOULD NOT STOP. MY FO CYCLED THE ANTI-SKID AND NOSEWHEEL STEERING SWITCH, ALSO WITH NO EFFECT. WE THEN COMMENCED ENG START TO OBTAIN HYD PRESSURE AND FORWARD THRUST. AT THE SAME TIME MY FO XMITTED TO GND CTL THAT WE HAD LOST OUR BRAKES, AND DIRECTED THE FLT ATTENDANTS TO BE IMMEDIATELY SEATED. AS THE #1 ENG SPOOLED UP I AGAIN RELEASED THE PARKING BRAKE AND USED THE BRAKE PEDALS TO STOP THE AIRPLANE SAFELY ON THE TXWY. NO ONE WAS INJURED AND NO DAMAGE OCCURRED. WE THEN HAD THE MECH HOOK THE TOW TRACTOR BACK UP TO OUR ACFT AND TOW US BACK TO THE GATE. AT THE GATE THE MECH EXPLAINED THAT THE BRAKE ACCUMULATOR HAD PROBABLY BEEN PARTIALLY DEPLETED DURING THE OVERNIGHT STAY AND THE ADDITIONAL MAINT RELEASE DOCUMENT ALTERNATE BRAKE CHK HAD FURTHER DEPLETED THE ACCUMULATOR TO THE POINT THE BRAKES WOULD NOT HOLD THE AIRPLANE IN PLACE ON THE SLOPED TXWY. AFTER CHARGING THE BRAKE ACCUMULATOR WITH THE YELLOW HYD SYS, WE ACCOMPLISHED ANOTHER ALTERNATE BRAKE CHK, AGAIN RECHARGED THE ACCUMULATOR, RESTARTED THE #1 ENG AT THE GATE, AND COMMENCED AN UNEVENTFUL PUSHBACK. THE A320 FLT HANDBOOK CONTAINS NO EMER PROC OR IRREGULAR PROC FOR BRAKE FAILURE. IT DOES CONTAIN A WARNING TO RELEASE THE PARKING BRAKE IN THE EVENT THE AIRPLANE STARTS MOVING DURING ENG START, BUT DOES NOT ADDRESS THE STARTING OF THE YELLOW HYD SYS ELECTRIC PUMP TO GAIN IMMEDIATE HYD PRESSURE. THE MAINT RELEASE DOCUMENT PROC FOR THE ALTERNATE BRAKE CHK DOES NOT CONTAIN A STEP TO RECHARGE THE BRAKE ACCUMULATOR AFTER PERFORMING THE CHK. 1) ADD A320 LOSS OF BRAKES EMER PROC TO INCLUDE: A) PARKING BRAKE -- RELEASE. B) YELLOW HYD SYS ELECTRIC PUMP -- ON. 2) ADD NEW STEP TO END OF A320 MAINT RELEASE DOCUMENT ALTERNATE BRAKE CHK: RECHARGE BRAKE ACCUMULATOR WITH YELLOW HYD SYS ELECTRIC PUMP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE REQUIRED CHK FOR THE DEFERRED ITEM DEPLETED THE YELLOW SYS ACCUMULATOR AND WAS NOT REPLENISHED WITH THE YELLOW ELECTRIC HYD PUMP. THE APU WAS RUNNING AND #1 ENG WAS STARTED AND SUPPLIED HYD PRESSURE FOR THE NORMAL BRAKING SYS.

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.