Narrative:

The aircraft had bscu (break steering control unit) two and aft cargo heat inoperative. The brake issue required a check of the alternate brake system which required brakes chocked. We checked; yellow system worked and continued. At brakes set; accumulator pressure dropped to the 6 o'clock position which is almost a 1;000 psi drop. Since bscu 2 was MEL'ed; I had to review what would happen if we lost bscu 1 also. The brake system would revert to yellow system pressure only with manual applications of brakes; maximum 1;000 psi. It would be very easy to over step and blow tires in this condition. What concerned me more was the loss of yellow system pressure would also force us into emergency braking on the accumulator which had just shown a major drop of 1;000 psi on its first brake application. I notified maintenance; and asked for guidance; making sure he was aware of this situation. We took a two minute delay performing the brake check at the gate after brake release. We were number ten for takeoff and had at least another twelve minutes plus on taxi in addition to the four minutes to start both motors. We waited another eight minutes for maintenance to confirm their acceptance of this situation. Then we entered the takeoff queue again. My concern is the levels of safety are starting to erode. We should fix these aircraft at maintenance stations with braking type problems. Granted a yellow system and bscu 1 failure is remote but; given the potential outcome; I feel the risk is not worth it. I also called the duty manager to explain this issue and found he was over worked and could not help in a timely manner.

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Original NASA ASRS Text

Title: An A320 Captain reported concern over being dispatched with BSCU 2 (Break Steering Control Unit) inoperative.

Narrative: The aircraft had BSCU (Break Steering Control Unit) two and aft cargo heat inoperative. The brake issue required a check of the alternate brake system which required brakes chocked. We checked; yellow system worked and continued. At brakes set; accumulator pressure dropped to the 6 o'clock position which is almost a 1;000 PSI drop. Since BSCU 2 was MEL'ed; I had to review what would happen if we lost BSCU 1 also. The brake system would revert to yellow system pressure only with manual applications of brakes; maximum 1;000 PSI. It would be very easy to over step and blow tires in this condition. What concerned me more was the loss of yellow system pressure would also force us into emergency braking on the accumulator which had just shown a major drop of 1;000 PSI on its first brake application. I notified Maintenance; and asked for guidance; making sure he was aware of this situation. We took a two minute delay performing the brake check at the gate after brake release. We were number ten for takeoff and had at least another twelve minutes plus on taxi in addition to the four minutes to start both motors. We waited another eight minutes for Maintenance to confirm their acceptance of this situation. Then we entered the takeoff queue again. My concern is the levels of safety are starting to erode. We should fix these aircraft at maintenance stations with braking type problems. Granted a yellow system and BSCU 1 failure is remote but; given the potential outcome; I feel the risk is not worth it. I also called the duty manager to explain this issue and found he was over worked and could not help in a timely manner.

Data retrieved from NASA's ASRS site as of April 2012 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.