What was found
DESCENDING FROM FL400 TO FL350 THE CAPTAIN FELT HIS EARS POPPING. HE LOOKED AT THE CABIN PRESSURE GAUGE AND NOTICED IT FLUCTUATING FROM 0-500 FT/MIN BEFORE JUMPING TO 5500 FT/MIN. THE CREW PUT ON THEIR OXYGEN MASKS. THE RED CABIN ALT LIGHT ILLUMINATED, AND THE CREW PROCEEDED TO CARRY OUT THE EMERGENCY DESCENT PROCEDURE. THE MASKS IN THE CABIN DEPLOYED. THE ACFT LANDED WITHOUT ANY FURTHER PROBLEMS. MAINTENANCE R & R THE PRIMARY OUTFLOW VALVE AND THE PRESSURIZATION CONTROLLER. THE ACFT PRESSURIZATION CHECK WAS GOOD.