What was found
CREW REPORTED LOSS OF PRESSURE DESCENDING AT 1000FT/MIN AT 230 KNOTS. LOUD POPPING NOISE FROM THE R2 DOOR AREA. CABIN RATE INDICATION WAS PEGGED PASS 3000FT AND DROPPED TO ZERO. CABIN ALT STAYED AT 8500 THE WHOLE TIME AND WHEN THE ACFT REACHED 3000 IT STARTED DROPPING RAPIDLY. CABIN DIFF BLEED DOWN TO ZERO. THERE WAS NO DOOR INDICATIONS (ALL DOORS WERE SECURED). BLOW OUT PANEL WAS BLOWN OUT. NO CABIN PRESS WARNING LIGHTS ILLUM (MAYBE DUE TO THEY WERE BELOW ALT). CONTRACT MAINTENANCE IS IN ROUTE TO RE-SECURE THE BLOW OUT PANEL AND MEL THE CABIN PRESSURE. THEY WERE DESCENDING. REMOVED AND REPLACED CARGO DOOR SEAL, OPS CHECKED GOOD.