FLC LOST CTL OF PRESSURIZATION.

Narrative

CABIN ALT BEGAN TO CLB WHILE IN CRUISE AT 37000 FT. GOT WARNING LIGHT FOLLOWED BY VERBAL WARNING. FLT SAFETY MGR HAD JUST ENTERED COCKPIT. NOTIFIED ATC AND BEGAN DSCNT TO COMPLY WITH ESTABLISHED PROCS. NOTIFIED FLT SAFETY MGR TO PROCEED TO CABIN; MADE PA TO FLT ATTENDANTS AND PAX. CABIN WAS AT 10000 FT CLBING AT 1100-1500 FPM. MANUALLY DROPPED MASKS AND MADE PA TO PAX AND FLT ATTENDANTS TO DON MASKS. RECEIVED INTERCOM FROM FLT ATTENDANT THAT MASKS ON R SIDE DID NOT DEPLOY. HAD FO ATTEMPT DEPLOYMENT AGAIN WITHOUT SUCCESS. REALIZED THAT CABIN HAD STOPPED CLBING. MADE A PA THAT MASKS WERE NO LONGER NECESSARY SINCE CABIN HAD STOPPED CLBING AND WAS PRESSURIZING AGAIN (MAX CABIN REACHED WAS 10500 FT). CONTINUED DSCNT TO 10000 FT MSL UNTIL LNDG DSCNT WAS BEGUN. ALL PROCS (BOTH COCKPIT AND FLT ATTENDANT) WERE COMPLIED WITH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS FLYING AN MD-80. HE SAID HE WAS TOLD THE PRESSURIZATION PROB WAS A LARGE BLOCK OF ICE THAT WAS FOUND IN THE R RAM AIR DUCT AND A SMALLER BLOCK OF ICE THAT WAS FOUND IN THE L RAM AIR DUCT. HE SAID IT MAY BE JUST COINCIDENTAL BUT A BOEING 737 HAD TO DSND AHEAD BECAUSE OF A PRESSURIZATION PROB. HE SAID THE MASKS FOR THE ROW OF SEATS ON THE R SIDE OF THE ACFT DID NOT DROP BECAUSE OF A FAILED ELECTRICAL SOLENOID; BUT; THE MASKS WOULD HAVE DROPPED IF THE CABIN WENT ABOVE 14500 WHEN THE ANEROID SWITCH ACTIVATED THE MASKS TO DEPLOY. THE CABIN NEVER DID GO ABOVE 14500 FT TO TEST THAT THEORY. THE FLT ATTENDANTS DID WELL IN RELOCATING PAX FROM THE R SIDE TO THE L AS THE FLT WAS NOT FULL AND THERE WERE EXTRA SEATS TO ACCOMMODATE THAT. HE SAID HE DID NOT FEEL THE MD-80 PRESSURIZATION SYS WAS ADEQUATE AT FL370 WITH ALL ANTI- ICE ON.