A B737-800's main cabin door did not close completely even though the door appeared closed and the d...

Narrative:

Shortly after takeoff; a very loud noise came from the forward cabin door and the aircraft would not pressurize. Declared an emergency with ATC. Ran appropriate checklists. With the now extremely loud noise; difficulty communicating with the flight attendant; and true conditions of the door unknown; I elected to exercise captain's emergency authority and land overweight at our departure airport. Landing was uneventful. Maintenance determined that the cabin door was not closed/seated properly. An apparent 'false lock' of the door. All indications in the cockpit and flight attendant observations indicated the door was closed/armed prior to gate departure.

Original NASA ASRS Text

Title: A B737-800's main cabin door did not close completely even though the door appeared closed and the Door Warning system indicated no doors open. Because of the extremely loud noise in flight and the lack of pressurization; an emergency was declared and the flight returned to land.

Narrative: Shortly after takeoff; a very loud noise came from the forward cabin door and the aircraft would not pressurize. Declared an emergency with ATC. Ran appropriate checklists. With the now extremely loud noise; difficulty communicating with the flight attendant; and true conditions of the door unknown; I elected to exercise Captain's emergency authority and land overweight at our departure airport. Landing was uneventful. Maintenance determined that the cabin door was not closed/seated properly. An apparent 'false lock' of the door. All indications in the cockpit and flight attendant observations indicated the door was closed/armed prior to gate departure.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	863608
Time
Date	200912
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Night
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Climb Initial Climb
Flight Plan	IFR
Component
Aircraft Component	Door Warning System
Person 1
Function	First Officer Pilot Flying
Events
Anomaly	Aircraft Equipment Problem Less Severe

A B737-800's main cabin door did not close completely even though the door appeared closed and the door warning system indicated no doors open. Because of the extremely loud noise in flight and the lack of pressurization; an emergency was declared and the flight returned to land.