What was found
DURING CRUISE FL370, PACKS NR 1 & 2 OPERATING, NR 1 PACK AIRFLOW APPROX 20 PSI & NR 2 PACK AIRFLOW 33 PSI, CABIN BEGAN TO CLIMB RAPIDLY. RATE LIMIT LIGHT ON. CABIN SHOWED A MOMENTARY DESCENT THEN BEGAN TO CLIMB RAPIDLY. SELECTED MANUAL PRESSURE. CABIN CONTINUED TO CLIMB RAPIDLY & ALTITUDE WARNING HORN ON. THIRD PACK WAS TURNED ON & OUTFLOW VALVES IMMEDIATELY SELECTED TO CLOSE. CABIN CONTINUED TO CLIMB. EMERGENCY DESCENT INITIATED. AFTER RECTIFICATION OF APU, ALL 3 PACKS CHECKED OK FOR NORMAL OPS AS PER AMM 5-51-08. EXCESSIVE CABIN PRESSURE LEAK CHECK CARRIED OUT WITH GOOD RESULTS. CHECKED UP TO 4 PSI AT 500 V/S. PRESSURE BLKHDS ETC CHECKED NO DEFECTS OR LEAKS AS PER 5-51-08. A/C SERVICEABLE. (M)