B737-500 RETURNS TO PDX FOR OVERWT LNDG WHEN UNABLE TO PRESSURIZE DUE TO IMPROPERLY SECURED EQUIP ACCESS DOOR.

Narrative

ON TKOF FROM PDX; WE NOTICED IMMEDIATELY THAT THE ACFT WAS NOT PRESSURIZING. WE CHKED TO SEE THAT THE APPROPRIATE SWITCHES WERE IN THE CORRECT POS; AND FOUND THAT THE PRESSURIZATION CTL PANEL WAS PROPERLY CONFIGURED; AND THAT THE OUTFLOW VALVE WAS FULLY CLOSED. WE ELECTED TO LEVEL OFF AT 8000 FT TO FURTHER INVESTIGATE THE PROB. PASSING ABOUT 5000 FT; WE GOT AN AUTOFAIL LIGHT FOR THE PRESSURIZATION SYS; AND SWITCHED TO STANDBY. PASSING 6000 FT; THE EQUIP DOOR LIGHT CAME ON; WHICH CONVINCED US THE DOOR HAD SOMEHOW COME OPEN INFLT; PREVENTING THE ACFT FROM PRESSURIZING. THE CAPT TRIED TO TALK TO DISPATCH; BUT COLD NOT GET A GOOD PHONE PATCH; WE SUSPECT DUE TO OUR ALT. WE INFORMED PDX OPS OF OUR SIT AND ELECTED TO RETURN TO PDX FOR WHAT WOULD BE AN OVERWT LNDG (APPROX 116000 LBS). THE LNDG WAS UNEVENTFUL; AND WE RETURNED TO THE CHOCKS AT PDX WHERE MAINT ASSISTED US WITH CHKING THE EQUIP BAY DOOR AND CHKING FOR HOT BRAKES. ONCE EVERYTHING WAS CHKED OUT AND WE RECEIVED MORE FUEL; WE CONTINUED WITH OUR FLT TO DEN UNEVENTFULLY.