Narrative:

En route while climbing through approx 35K we heard a moderately loud pop sound (from somewhere in forward part of airplane) which didn't sound like the usual surge in bleed air noise that occurs in ce-680's at 37;300 ft. We noted that the cabin rate of climb which had been about 500 fpm increased to approx 1000 FPM and as a precaution; we donned our masks. We were flying from a low altitude airport to a high altitude airport so with the pressure controller set to field elevation; we thought that maybe the pressurization controller was just having difficulty controlling the cabin rate as it was adjusting to the high landing field elevation. The cabin rate of climb settled down to zero after the 1-2 min spike to 1000 FPM and cabin altitude had climbed to landing field elevation and had stabilized there. We were still not sure what the pop sound was. We called the duty manager and discussed the pop and cabin rate of climb spike. Because the pressurization system seemed to be working normally thereafter; we said we were comfortable continuing but would monitor the pressurization system for any further abnormalities. We completed the approach with no irregular spikes in cabin rate and the cabin was close to 0 delta p (normal) before performing a normal landing. Because the pressurization system appeared to be operating normally; we elected to accept the next leg. The airplane pressurized normally on the initial climb out (checked normal while performing the climb checklist and no popping of ears felt) and while climbing through approximately 29000 ft; the amber 'cabin altitude' annunciation came on and we performed the memory items for 'loss of cabin pressure' (masks; etc); declared an emergency (because of previous leg's pressurization problem - elected to be conservative and divert); requested a lower altitude and asked to divert. After completing the memory items; I elected to select the passenger oxygen on (because of the previous legs pressurization problem and possibility the cabin altitude could rise quickly) and verified that the passengers had put on their masks and were doing ok. I chose to do the loss of pressurization and emergency descent checklists vs. The amber 'cabin altitude' checklist because the pop sound from the previous leg made me think that it was possibly a continued pressurization problem which could get more serious. Shortly after the amber cabin altitude came on; the red 'cabin altitude' annunciator came on. By then we were in the descent to a lower altitude and were addressing the cabin altitude situation (which appeared to be maintaining about 9500 to 10000 ft pressurization switch positions all checked normal). We coordinated with ATC for continued lower altitude; completed the checklists and were vectored for a visual approach to our divert airport without further complications. The total time from the cabin altitude annunciation coming on to landing was approximately 10 to 15 minutes.

Related reports:

Google
 

Original NASA ASRS Text

Title: CE680 flight crew experienced loss of cabin pressurization climbing through FL290 and elected to divert to a suitable airport. Pressurization anomalies had been noted on the previous leg but no maintenance action was taken.

Narrative: En route while climbing through approx 35K we heard a moderately loud pop sound (from somewhere in forward part of airplane) which didn't sound like the usual surge in bleed air noise that occurs in CE-680's at 37;300 FT. We noted that the cabin rate of climb which had been about 500 fpm increased to approx 1000 FPM and as a precaution; we donned our masks. We were flying from a low altitude airport to a high altitude airport so with the pressure controller set to field elevation; we thought that maybe the pressurization controller was just having difficulty controlling the cabin rate as it was adjusting to the high landing field elevation. The cabin rate of climb settled down to zero after the 1-2 min spike to 1000 FPM and cabin altitude had climbed to landing field elevation and had stabilized there. We were still not sure what the pop sound was. We called the Duty Manager and discussed the pop and cabin rate of climb spike. Because the pressurization system seemed to be working normally thereafter; we said we were comfortable continuing but would monitor the pressurization system for any further abnormalities. We completed the approach with no irregular spikes in cabin rate and the cabin was close to 0 delta p (normal) before performing a normal landing. Because the pressurization system appeared to be operating normally; we elected to accept the next leg. The airplane pressurized normally on the initial climb out (checked normal while performing the climb checklist and no popping of ears felt) and while climbing through approximately 29000 FT; the amber 'CABIN ALT' annunciation came ON and we performed the memory items for 'Loss of Cabin Pressure' (masks; etc); declared an emergency (because of previous leg's pressurization problem - elected to be conservative and divert); requested a lower altitude and asked to divert. After completing the memory items; I elected to select the Passenger Oxygen ON (because of the previous legs pressurization problem and possibility the cabin altitude could rise quickly) and verified that the passengers had put on their masks and were doing ok. I chose to do the loss of pressurization and emergency descent checklists vs. the amber 'cabin altitude' checklist because the pop sound from the previous leg made me think that it was possibly a continued pressurization problem which could get more serious. Shortly after the amber cabin altitude came on; the red 'cabin altitude' annunciator came on. By then we were in the descent to a lower altitude and were addressing the cabin altitude situation (which appeared to be maintaining about 9500 to 10000 FT pressurization switch positions all checked normal). We coordinated with ATC for continued lower altitude; completed the checklists and were vectored for a visual approach to our divert airport without further complications. The total time from the cabin altitude annunciation coming on to landing was approximately 10 to 15 minutes.

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.