What was found
SHIP 3809 -PRESS- DESCENDING OUT OF FL200 CABIN ALT WARNING OCCURRED. DONNED O2 MASKS AND DESCENDED TO 11K. LEFT PACK ON MEL. CORRECTIVE ACTION: PERFORMED RT ENGINE PNEUMATIC HEALTH CHECK. REPLACED RT ENGINE PRSOV, HSV, AND HSR. RT BLEED CHECKS GOOD. REPLACED LEFT PACK FCV, TCV AND BOTH HEAT EXCHANGERS. PERFORMED CABIN PRESSURE LEAK CHECK. REPLACED MULTIPLE LOWER FUSELAGE DRAINS, TIGHTENED EQUIPMENT COOLING EXHAUST VALVE CLAMP AND RESEALED AFT CARGO DOOR THRESHOLD. PACK CONFIDENCE CHECK GOOD.