A CE560 first officer reported a door not locked annunciation; all doors were verified closed. Later...

Narrative:

During our climb to FL410; we received a 'door not locked' annunciation. This annunciation is triggered by the lock assembly of either nose baggage door; aft baggage door or the main entry door. All doors were confirmed locked and the annunciation was extinguished prior to engine start. The annunciation panel was again confirmed 'clear' prior to takeoff. After confirming the main cabin door locking pins all indicated closed; the door was properly closed and in the locked position; we attributed the annunciation to be a false indication. Shortly after leveling at 41;000 ft; a faint 'squeal' began coming from the main cabin door seal. All environmental system indications remained normal. We asked for a descent to FL390 in an effort to alleviate some differential pressure and were cleared as requested. Before we could begin the descent; the 'cabin door seal' annunciation illuminated and the cabin began climbing to about 500 FPM. I; as the flying pilot; donned my oxygen mask. The captain asked for a lower altitude; however; the center controller would not clear us below FL390. Within seconds the cabin altitude became uncontrollable and began climbing in excess of 6000 FPM. The captain declared an emergency and an emergency descent was initiated. After communicating with ATC; we diverted to the nearest suitable airport where we could both clear customs and have repairs made.

Original NASA ASRS Text

Title: A CE560 First Officer reported a DOOR NOT LOCKED annunciation; all doors were verified closed. Later; a main cabin door squeal developed; then a CABIN DOOR SEAL annunciation and the cabin began climbing at 6;000 FPM. An emergency was declared and the flight diverted to a nearby airport.

Narrative: During our climb to FL410; we received a 'Door Not Locked' annunciation. This annunciation is triggered by the lock assembly of either nose baggage door; aft baggage door or the main entry door. All doors were confirmed locked and the annunciation was extinguished prior to engine start. The annunciation panel was again confirmed 'clear' prior to takeoff. After confirming the main cabin door locking pins all indicated closed; the door was properly closed and in the locked position; we attributed the annunciation to be a false indication. Shortly after leveling at 41;000 FT; a faint 'squeal' began coming from the main cabin door seal. All environmental system indications remained normal. We asked for a descent to FL390 in an effort to alleviate some differential pressure and were cleared as requested. Before we could begin the descent; the 'cabin door seal' annunciation illuminated and the cabin began climbing to about 500 FPM. I; as the flying pilot; donned my oxygen mask. The Captain asked for a lower altitude; however; the Center Controller would not clear us below FL390. Within seconds the cabin altitude became uncontrollable and began climbing in excess of 6000 FPM. The Captain declared an emergency and an emergency descent was initiated. After communicating with ATC; we diverted to the nearest suitable airport where we could both clear customs and have repairs made.

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	955488
Time
Date	201106
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Citation V/Ultra/Encore (C560)
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Exterior Pax/Crew Door
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 90 Flight Crew Total 2800
Events
Anomaly	Aircraft Equipment Problem Critical

A CE560 first officer reported a door not locked annunciation; all doors were verified closed. Later; a main cabin door squeal developed; then a cabin door seal annunciation and the cabin began climbing at 6;000 FPM. An emergency was declared and the flight diverted to a nearby airport.