What was found
AIRCRAFT PERFORMED AN EMERGENCY DESCENT 20 MINUTES PRIOR TO LANDING, DUE TO UNCONTROLLABLE DEPRESSURATION. MAINTENANCE PERSONNEL VERIFIED THE PNEUMATIC SYSTEM FOR LEAKS AS WELL AS THE AIR CONDITIONED SYSTEM AND THE DUCTS OF ANTI-ICE SYSTEM IAW MPCM 36-10-00, 21-10-00 AND 30-10-00, ALL CORRECT. PRESSURIZATION TESTS WAS PERFORMED WITH BOTH ENGINES IAW MM 21-30-00, ALL CORRECT. DURING CABIN CHECK, THE SW (RADIO RACK) WAS CHANGED FROM VENTURY TO FAN POSITION, TESTED CORRECT.