What was found
BTB - PILOT REPORTED, DURING TAXI OUT FOR T/O THE NR 2 B-PUMP LOW PRESSURE LIGHT CAME ON, FOLLOWED BY THE NR 1 B-PUMP LOW PRESSURE LIGHT, 2 MIN LATER. THEN THE B SYSTEM PRESSURE DROPPED TO ZERO. THE BRAKE PRESSURE DROPPED TO 1,000 PSI, ACCUMULATOR PRECHARGE AND THE A-SYSTEM QUANTITY DROPPED STEADILY 70, MAINTAINED 2.5 GALLONS. THE B-SYSTEM QUANTITY DROPPED TO 1.5 GALLONS FROM FULL AND HELD STEADY. BRAKE EFFECTIVENESS STEADILY DETERIOATED UNTIL ALL BRAKE ACTION WAS LOST. FOUND PRESSURE LINE ON B-PUMP NR 2 BLOWN. REPLACED LINE, LEAK CHECKS OK. OPERATED BRAKES AND ASSOCIATED HYD SYSTEMS, NO DEFECTS NOTED AND SERVICED HYD SYSTEM.