Narrative:

I am a captain with air carrier flying medium large transport based in sfo. While flying flight xx sfo lax feb/mon/90 at FL250 (because one aircraft pack was inoperative) the master caution warning light and door annunciator light on the forward glare shield came on and the door unlocked light on the overhead panel came on. I was flying with a new copilot (3RD line trip). I turned on the seat belt sign and told my copilot to make an announcement to the passenger to fasten their seat belts. I called ZLA and requested an immediate clearance to 16000'. I received a turn right to heading 180 and descend to FL240 due traffic 3 mi ahead (I assumed same direction). After establishing on heading 180 I declared an emergency and continued my descent to 16000 and was then cleared to first 11000 then 10000. The cabin pressure remained normal. We landed at lax at XA10 local. I had radioed for a maintenance supervisor to meet the aircraft and inspect the aft cargo door before anyone opened it. He and an FAA inspector did check the door and it was closed. I felt at the time the light came on that we might lose cabin pressure and it was safer to descend without clearance from ATC in VFR conditions. My flight manual is somewhat vague, ie, one pack operation -- if only one pack is available, consider continuing flight at 25000' or below. Door warning light on -- flight may continue at captain's discretion if pressurization is normal. I also feel a warning light that may be ignored is bad basic policy. Also the maintenance fix on this problem is to disarm the light so why do we have it?

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Original NASA ASRS Text

Title: AFT CARGO DOOR WARNING LIGHT CAME ON DURING CRUISE FLT. EMERGENCY DECLARED.

Narrative: I AM A CAPT WITH ACR FLYING MLG BASED IN SFO. WHILE FLYING FLT XX SFO LAX FEB/MON/90 AT FL250 (BECAUSE ONE ACFT PACK WAS INOP) THE MASTER CAUTION WARNING LIGHT AND DOOR ANNUNCIATOR LIGHT ON THE FORWARD GLARE SHIELD CAME ON AND THE DOOR UNLOCKED LIGHT ON THE OVERHEAD PANEL CAME ON. I WAS FLYING WITH A NEW COPLT (3RD LINE TRIP). I TURNED ON THE SEAT BELT SIGN AND TOLD MY COPLT TO MAKE AN ANNOUNCEMENT TO THE PAX TO FASTEN THEIR SEAT BELTS. I CALLED ZLA AND REQUESTED AN IMMEDIATE CLRNC TO 16000'. I RECEIVED A TURN RIGHT TO HDG 180 AND DSND TO FL240 DUE TFC 3 MI AHEAD (I ASSUMED SAME DIRECTION). AFTER ESTABLISHING ON HDG 180 I DECLARED AN EMER AND CONTINUED MY DSCNT TO 16000 AND WAS THEN CLRED TO FIRST 11000 THEN 10000. THE CABIN PRESSURE REMAINED NORMAL. WE LANDED AT LAX AT XA10 LCL. I HAD RADIOED FOR A MAINT SUPVR TO MEET THE ACFT AND INSPECT THE AFT CARGO DOOR BEFORE ANYONE OPENED IT. HE AND AN FAA INSPECTOR DID CHECK THE DOOR AND IT WAS CLOSED. I FELT AT THE TIME THE LIGHT CAME ON THAT WE MIGHT LOSE CABIN PRESSURE AND IT WAS SAFER TO DSND WITHOUT CLRNC FROM ATC IN VFR CONDITIONS. MY FLT MANUAL IS SOMEWHAT VAGUE, IE, ONE PACK OPERATION -- IF ONLY ONE PACK IS AVAILABLE, CONSIDER CONTINUING FLT AT 25000' OR BELOW. DOOR WARNING LIGHT ON -- FLT MAY CONTINUE AT CAPT'S DISCRETION IF PRESSURIZATION IS NORMAL. I ALSO FEEL A WARNING LIGHT THAT MAY BE IGNORED IS BAD BASIC POLICY. ALSO THE MAINT FIX ON THIS PROBLEM IS TO DISARM THE LIGHT SO WHY DO WE HAVE IT?

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.