What was found
NR 2 ENGINE PNEUMATIC BLEED TRIP INDICATION, 10 MINUTES LATER NR 1 ENG PNEUMATIC BLEED TRIPPED, DID EMERGENCY DESCENT AND PAX O2 MASKS DROPPED PER QRH. C/W PNEU BLEED SYS CONFIDENCE CHECKS PER SWA MT'S. REMOVED AND REPLACED BOTH ENGINES PNEU BLEED PRECOOLER CONTROL VALVES, HIGH STG REGULATORS & HIGH STG VALVES PER MM.