A321
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Confusion; Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Human Factors; Procedure
Taxi out for takeoff; made several stops and set parking brake prior to incident. [While] on taxiway; in line for takeoff with parking brake set; the aircraft rolled with the parking brake handle in the 'On' position. Stopped the aircraft with foot brakes. Cycled the parking brake handle multiple times with no brake pressure indication. Returned to the gate and made a logbook entry. The parking brake returned to normal operation with the engines shut down. Gate turnback. Mechanical.
Reporter stated there was no Yellow Hydraulic System pressure to the brakes showing on the Yellow Hydraulic System Triple Indicator when he set the parking brake handle to 'On' while waiting in-line for takeoff. When he taxied back to the gate; the problem still existed until he shut down both engines. The Generator Control Relay (GCR) sensed the engines spooling down and auto switched to APU electrical power. The parking brakes worked just fine after that; he could not duplicate the same problem.Reporter stated Maintenance did perform BITE Tests; but no faults were noted. However; mechanics troubleshooting the system informed him they believed a transmitter associated with the parking brake handle that sends a signal to a parking brake valve in the wheel well was responsible for the lack of Yellow hydraulic pressure availability; they just could not duplicate the problem either. Why that yellow pressure suddenly became available; after engine generator power was auto-switched to APU electrical power at the gate has not been answered. He was quite upset about the unexplained movement of the A321 aircraft with the parking brakes set and called their Chief Pilot shortly after they had returned to the gate. The Chief Pilot informed him that a similar incident had occurred approximately one week earlier on another A321; where the pilot reported they had started engines during the pushback; set the parking brake handle and as the Pushback Ground crew was disconnecting the towbar; the aircraft began to roll forward.Reporter stated that since his incident and knowing of other similar situations with the parking brake not holding; he will not start engines until the Pushback Ground crew has completely disconnected and left the aircraft. He no longer trusts the parking brakes to hold; especially since no faults are indicated when Maintenance performs system BITE Tests. He hopes Airbus will correct the problem soon.
A321 Captain reported he had set the parking brake handle to the 'On' position while waiting in line for takeoff; but the aircraft still rolled forward; he used foot brakes to stop the aircraft. While cycling the parking brake handle multiple times; he noticed the lack of brake pressure on the Yellow Hydraulic System Triple Indicator. Aircraft was taxied back to gate.