Narrative:

We departed normally from ZZZ. Passing about 3000 ft MSL, the 'a' flight attendant called to tell us that there was a loud noise coming from the forward entry door. We thought that it might be an improperly seated door seal and asked her to let us know if it got better or worse in the next few minutes. Passing 8000 ft MSL, we started monitoring the cabin pressure. It climbed through 8000 ft MSL and we leveled off at 10000 ft MSL with cabin altitude at 10000 ft. Just as we requested descent back down to 8000 ft, the cabin altitude warning horn went off. I put on my oxygen mask and we informed center that we would need to hold in order to burn down and land. At the time, we had about 24K fuel with a gw of about 132K. We held west of ZZZ at 8000 ft MSL with the gear and flaps down in order to burn down quicker. After talking to dispatch, it was decided to go over to ZZZ1, which at the time was 177 NM away. I informed the passenger, and center cleared us direct to ZZZ1 at 8000 ft. We left the door closed at the gate so maintenance could look at it from the outside. It turned out that when the operations agent at ZZZ closed the door, only the forward latches had fully engaged. Apparently the micro switches for the 'door open' lights are located by the forward latches. This explains why the 'door open' lights were never illuminated. Also, due to the storage bins on the forward bulkhead of the -700, it was very difficult to see from the flight attendant position that the rear latches weren't engaged properly. From the outside, however, it was fairly obvious. I believe that maintenance took some pictures before opening the door. We wrote it up, maintenance signed it off and we continued to ZZZ3 about 2 hours late. My intention in filling out this report in addition to an irregularity report is to point out the potential safety hazard that may exist if this should happen again. As I mentioned, there was no warning light indication despite the fact that the door was improperly closed. Callback conversation with reporter revealed the following information: the reporter stated that with over 8000 hours in B737 aircraft, the reporter was unaware an entrance door could be false latched and have no indication of its condition. The reporter said on arrival at the diversion station and before the door was opened, an interior inspection was performed by the flight crew and cabin attendants and there was no way this door could not be closed and latched. The reporter said an external inspection revealed the aft end of the door stuck out with the forward end closed and faired with the fuselage.

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Original NASA ASRS Text

Title: A B737-700 AT 8000 FT DECLARED AN EMER AND DIVERTED DUE TO BEING UNABLE TO PRESSURIZE THE ACFT. FOUND FORWARD ENTRANCE FALSE LATCHED WITH NO DOOR WARNING LIGHT.

Narrative: WE DEPARTED NORMALLY FROM ZZZ. PASSING ABOUT 3000 FT MSL, THE 'A' FA CALLED TO TELL US THAT THERE WAS A LOUD NOISE COMING FROM THE FORWARD ENTRY DOOR. WE THOUGHT THAT IT MIGHT BE AN IMPROPERLY SEATED DOOR SEAL AND ASKED HER TO LET US KNOW IF IT GOT BETTER OR WORSE IN THE NEXT FEW MINUTES. PASSING 8000 FT MSL, WE STARTED MONITORING THE CABIN PRESSURE. IT CLIMBED THROUGH 8000 FT MSL AND WE LEVELED OFF AT 10000 FT MSL WITH CABIN ALT AT 10000 FT. JUST AS WE REQUESTED DSCNT BACK DOWN TO 8000 FT, THE CABIN ALT WARNING HORN WENT OFF. I PUT ON MY OXYGEN MASK AND WE INFORMED CENTER THAT WE WOULD NEED TO HOLD IN ORDER TO BURN DOWN AND LAND. AT THE TIME, WE HAD ABOUT 24K FUEL WITH A GW OF ABOUT 132K. WE HELD WEST OF ZZZ AT 8000 FT MSL WITH THE GEAR AND FLAPS DOWN IN ORDER TO BURN DOWN QUICKER. AFTER TALKING TO DISPATCH, IT WAS DECIDED TO GO OVER TO ZZZ1, WHICH AT THE TIME WAS 177 NM AWAY. I INFORMED THE PAX, AND CENTER CLEARED US DIRECT TO ZZZ1 AT 8000 FT. WE LEFT THE DOOR CLOSED AT THE GATE SO MAINT COULD LOOK AT IT FROM THE OUTSIDE. IT TURNED OUT THAT WHEN THE OPS AGENT AT ZZZ CLOSED THE DOOR, ONLY THE FORWARD LATCHES HAD FULLY ENGAGED. APPARENTLY THE MICRO SWITCHES FOR THE 'DOOR OPEN' LIGHTS ARE LOCATED BY THE FORWARD LATCHES. THIS EXPLAINS WHY THE 'DOOR OPEN' LIGHTS WERE NEVER ILLUMINATED. ALSO, DUE TO THE STORAGE BINS ON THE FORWARD BULKHEAD OF THE -700, IT WAS VERY DIFFICULT TO SEE FROM THE FA POSITION THAT THE REAR LATCHES WEREN'T ENGAGED PROPERLY. FROM THE OUTSIDE, HOWEVER, IT WAS FAIRLY OBVIOUS. I BELIEVE THAT MAINT TOOK SOME PICTURES BEFORE OPENING THE DOOR. WE WROTE IT UP, MAINT SIGNED IT OFF AND WE CONTINUED TO ZZZ3 ABOUT 2 HOURS LATE. MY INTENTION IN FILLING OUT THIS REPORT IN ADDITION TO AN IRREGULARITY RPT IS TO POINT OUT THE POTENTIAL SAFETY HAZARD THAT MAY EXIST IF THIS SHOULD HAPPEN AGAIN. AS I MENTIONED, THERE WAS NO WARNING LIGHT INDICATION DESPITE THE FACT THAT THE DOOR WAS IMPROPERLY CLOSED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT WITH OVER 8000 HOURS IN B737 ACFT, THE RPTR WAS UNAWARE AN ENTRANCE DOOR COULD BE FALSE LATCHED AND HAVE NO INDICATION OF ITS CONDITION. THE RPTR SAID ON ARR AT THE DIVERSION STATION AND BEFORE THE DOOR WAS OPENED, AN INTERIOR INSPECTION WAS PERFORMED BY THE FLT CREW AND CABIN ATTENDANTS AND THERE WAS NO WAY THIS DOOR COULD NOT BE CLOSED AND LATCHED. THE RPTR SAID AN EXTERNAL INSPECTION REVEALED THE AFT END OF THE DOOR STUCK OUT WITH THE FORWARD END CLOSED AND FAIRED WITH THE FUSELAGE.

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.