DH8-100 FLC EXPERIENCED PROBS WITH BREATHING AND DISCOVERED CABIN ALT WARNING HAD FAILED TO ILLUMINATE; AS DESIGNED. ACFT WAS DSNDED TO A SAFE ALT; EMER CHKLIST ITEMS WERE COMPLETED; AND FLT CONTINUED TO DEST.

Narrative

WHILE CLBING TO OUR ASSIGNED ALT OF FL180; BOTH CREW MEMBERS NOTED AN APPARENT LOSS OF CABIN PRESSURIZATION. BEGAN DSCNT TO 14000 FT WHILE CAPT BEGAN EMER CHKLIST. AFTER CYCLING ALL PRESSURIZATION CTLS WE REGAINED CTL OF CABIN ALT. MAX CABIN ALT APPROX 11500 FT. 'CABIN PRESSURIZATION' EMER CAPTION LIGHT FAILED TO LIGHT AT 10000 FT AS DESIGNED. CABIN PRESSURE BEGAN TO DSND NORMALLY TO NORMAL ALT. SEVERAL SICK PAX RPTED BY FLT ATTENDANT. DSNDED TO 10000 FT AS PER EMER PROCS AND CONTINUED TO DEST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CAPT STATES THAT THE PROB IS THAT THERE IS NO COCKPIT PROC TO TEST THE FUNCTION OF THE CABIN PRESSURIZATION EMER WARNING SYS; AND HE IS UNCERTAIN ABOUT MAINT CHKS. (CABIN CTLR PROBS; ONLY; ARE CHKED BY A BUILT-IN TEST FUNCTION WHICH CAUSES A FAULT LIGHT TO GO OUT WHEN A TEST IS SATISFACTORY.) THE POSSIBLE CAUSE OF THE PRESSURE LOSS WAS A FORWARD OUTFLOW VALVE THAT WAS STUCK IN AN OPEN POS. THE CAPT REMEMBERS CHKING THE CABIN ALT DURING THE CLB CHKLIST AT 2500 FT; AND RANDOMLY; AT 6000 FT. THERE WERE NO ABNORMAL INDICATIONS. CAPT STATES THAT A LESS EXPERIENCED CREW OR A LONGER DELAY IN THE FAILURE TO RECOGNIZE THE LOSS OF PRESSURIZATION; WOULD HAVE LED TO A FLT OUT OVER THE GULF. CAPT HAS RPTED THIS PROB TO THE COMPANY; AND NO ACTION TAKEN; SO FAR. SINCE THIS INCIDENT; THE RPTR CHKED ANOTHER DH8-100 WHILE ON A FERRY FLT; AND AGAIN; THE EMER CAPTION LIGHT DID NOT ILLUMINATE AT THE 10000 FT CABIN ALT. HE HAS CHKED WITH OTHER PLTS AND GUESSES THAT 50 PERCENT OF THE FLEET CABIN PRESSURE EMER CAPTION LIGHTS WILL NOT CHK OUT. THE CHKLISTS USED BY THE FLCS ARE SUPPLIED BY DEHAVILLAND AND MODIFIED BY THE COMPANY. THE RPTR BELIEVES THAT FLC CABIN ALT WARNING CHKS ARE NONEXISTENT. SUPPLEMENTAL INFO FROM ACN 321307: BOTH CREW MEMBERS WENT ON OXYGEN. FIRST INDICATION OF PROB WAS SHORTNESS OF OXYGEN AND PROBS BREATHING.