A CESSNA 560X ON A VISUAL APCH AT 3000 FT HAD THE EMER PRESSURE VALVE CYCLE OPEN AND CLOSE WITH A DEAFENING ROAR CAUSING A LOSS OF COMMUNICATION.

Narrative

WHEN APPROACHING ISM WE WERE AT 3000 FT AND TOLD TO REPORT ISM FOR THE VISUAL APCH WE SAW THE ARPT AND CALLED IN SIGHT; I EXPECTED TO BE CLEARED FOR VISUAL AND AT THE TIME OF ATC ANSWER WE HAD AN EMER PRESSURE VALVE OPEN IN THE ACFT AND SHUT OFF AUTO (IT CYCLED) ON AND OFF. WITH NO WARNING LIGHT. BECAUSE THIS WAS NOT ADDRESSED IN POSSIBLE CHKLST PROC;. WE STUMPED AND DISTRACTED. I ASSUMED WE WERE CLEARED FOR THE VISUAL TO RWY 15 BUT MY COPLT DID NOT ADVISE THAT WE WERE TO MAINTAIN 3000 FEET. WE LEFT 3000 FT FOR 2000 FT AND THEN CANCELED IFR AND WAS TOLD THAT WE SHOULD NOT HAVE LEFT 3000 FT. CESSNA SAYS EXCELS (560) ARE EXPERIENCING BAD EMER PRESSURE VALVES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE EMER PRESSURE VALVE OPENS WHEN A LOSS OF CABIN PRESSURE OCCURS AND DUMPS ENG BLEED AIR DIRECTLY INTO THE CABIN. THE RPTR SAID THIS AIRPLANE IS ON ITS THIRD VALVE AND WILL NEED ANOTHER VALVE WHEN CESSNA COMES UP WITH A MODIFIED VALVE TO CORRECT ITS CURRENT PROBLEMS. THE RPTR SAID THE PROBLEM IS THE SPRING PRESSURE IN THE VALVE IS NOT ADEQUATE MAINLY BECAUSE THE AIRPLANES HAVE HAD UPRGRADED HIGHER THRUST ENGS INSTALLED. THE RPTR STATED THIS IS AN ONGOING PROBLEM WITH THE 560X MODEL. THE RPTR STATED THAT WHEN THIS VALVE OPENS UP THE NOISE IS ALMOST UNBEARABLE AND THE CABIN GETS REAL WARM.