Narrative:

While in cruise at FL430 a squeal suddenly developed in the cockpit. My flight mechanic investigated and reported that we had a leak in the main cabin door seal. The aircraft was having no trouble maintaining cabin pressure. We were approaching an area of WX and decided that after deviating south we would descend to lower the cabin differential pressure and continue. A few mins later there was a sudden increase in pitch and volume of the sound. The cabin altitude began to climb at around 1500 FPM. The outflow valve was fully closed and the cabin continued to climb. I donned my oxygen mask (the first officer was already wearing his) and called for the 'loss of pressurization' checklist. I commanded first officer to declare an emergency and get direct ZZZ. Center cleared us to 10000 ft and direct ZZZ. I initiated a right turn and began the descent in accordance with the QRH. At 10000 ft we removed our mask and got a handoff to ZZZ approach. ZZZ gave us vectors for runway xxr. I requested and was given the inbound course and localizer frequency for the runway. We also requested that ATC notify united states customs of our diversion. We completed a visual approach to runway xxr and landed without incident. We taxied to united states customs and cleared about an hour later. The flight mechanic notified me that between FL200 and FL250 the cabin began to stabilize; probably due to the decrease in differential pressure. On further investigation he discovered that the door seal had 'rolled' out of its track; most likely when we closed it on departure.

Related reports:

Google
 

Original NASA ASRS Text

Title: G400 CAPTAIN REPORTS PRESSURIZATION PROBLEMS CAUSED BY A DOOR SEAL AT FL430 REQUIRING AN EMERGENCY DESCENT AND DIVERSION.

Narrative: WHILE IN CRUISE AT FL430 A SQUEAL SUDDENLY DEVELOPED IN THE COCKPIT. MY FLT MECH INVESTIGATED AND RPTED THAT WE HAD A LEAK IN THE MAIN CABIN DOOR SEAL. THE ACFT WAS HAVING NO TROUBLE MAINTAINING CABIN PRESSURE. WE WERE APCHING AN AREA OF WX AND DECIDED THAT AFTER DEVIATING S WE WOULD DSND TO LOWER THE CABIN DIFFERENTIAL PRESSURE AND CONTINUE. A FEW MINS LATER THERE WAS A SUDDEN INCREASE IN PITCH AND VOLUME OF THE SOUND. THE CABIN ALT BEGAN TO CLB AT AROUND 1500 FPM. THE OUTFLOW VALVE WAS FULLY CLOSED AND THE CABIN CONTINUED TO CLB. I DONNED MY OXYGEN MASK (THE FO WAS ALREADY WEARING HIS) AND CALLED FOR THE 'LOSS OF PRESSURIZATION' CHKLIST. I COMMANDED FO TO DECLARE AN EMER AND GET DIRECT ZZZ. CTR CLRED US TO 10000 FT AND DIRECT ZZZ. I INITIATED A R TURN AND BEGAN THE DSCNT IN ACCORDANCE WITH THE QRH. AT 10000 FT WE REMOVED OUR MASK AND GOT A HDOF TO ZZZ APCH. ZZZ GAVE US VECTORS FOR RWY XXR. I REQUESTED AND WAS GIVEN THE INBOUND COURSE AND LOC FREQ FOR THE RWY. WE ALSO REQUESTED THAT ATC NOTIFY UNITED STATES CUSTOMS OF OUR DIVERSION. WE COMPLETED A VISUAL APCH TO RWY XXR AND LANDED WITHOUT INCIDENT. WE TAXIED TO UNITED STATES CUSTOMS AND CLRED ABOUT AN HR LATER. THE FLT MECH NOTIFIED ME THAT BTWN FL200 AND FL250 THE CABIN BEGAN TO STABILIZE; PROBABLY DUE TO THE DECREASE IN DIFFERENTIAL PRESSURE. ON FURTHER INVESTIGATION HE DISCOVERED THAT THE DOOR SEAL HAD 'ROLLED' OUT OF ITS TRACK; MOST LIKELY WHEN WE CLOSED IT ON DEP.

Data retrieved from NASA's ASRS site as of January 2009 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.