Narrative:

Flight was operating in cruise flight at FL390 in communication with ZZZ center. I felt my ears begin to pop and I checked the cabin altitude and rate. First officer noticed the pressure change at the same time and we noted the cabin rate of climb indicator pegged at the 2000 FPM limit. No annunciator lights or EICAS messages were indicated. The cabin altitude was approaching 10000 ft. We donned O2 masks and were unable to stop the cabin climb so I declared an emergency and told the first officer to initiate an emergency descent as I communicated with center and requested a diversion. As we initiated the descent the cabin altitude alert indicated with the associated master warning. The cabin altitude QRH procedure was completed while the first officer continued the descent. The cabin altitude climbed to approximately 13000 ft for a very short period of time before descending to approximately 2000 in preparation for our landing. My initial communication with the flight attendant was to advise him that we were experiencing pressurization problems and would be descending. I would contact him again when we knew more. As the aircraft approached 17000 I contacted the flight attendant and told him that we were unable to keep the aircraft pressurized and were diverting with a landing in 15 to 20 minutes. I asked him the condition of the cabin crew and passengers and he advised that all were fine and most knew nothing happened until we started our descent. The cabin never completely depressurized however the exact differential is not recalled. As we descended to 13000 ft with a cabin altitude of approximately 8000 ft I made a PA stating that we had experienced a cabin pressure problem and we were diverting for repairs. Normal approach and landing were made. Passengers were deplaned and maintenance met the aircraft to initiate troubleshooting on the pressurization problem. After the passengers were off the aircraft I gathered the cabin team together and again asked if they were alright and if they were aware of any passenger illness or difficulties. I was advised that everyone was 'fine' and no passengers communicated any ill effects. Repairs were made to a loose duct in the right pack bay. The passengers that wanted to continue to our planned destination were boarded and the flight continued with no further pressurization problems.

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Original NASA ASRS Text

Title: A B757's right pack ducting came loose in flight causing the cabin altitude to climb at 2;000 FPM. The crew declared an emergency; descended; diverted and finally gained control of the cabin below 17;000'.

Narrative: Flight was operating in cruise flight at FL390 in communication with ZZZ Center. I felt my ears begin to pop and I checked the cabin altitude and rate. First Officer noticed the pressure change at the same time and we noted the cabin rate of climb indicator pegged at the 2000 FPM limit. No annunciator lights or EICAS messages were indicated. The cabin altitude was approaching 10000 ft. We donned O2 masks and were unable to stop the cabin climb so I declared an emergency and told the First Officer to initiate an Emergency Descent as I communicated with Center and requested a diversion. As we initiated the descent the CABIN ALT alert indicated with the associated master warning. The CABIN ALTITUDE QRH procedure was completed while the First Officer continued the descent. The cabin altitude climbed to approximately 13000 ft for a very short period of time before descending to approximately 2000 in preparation for our landing. My initial communication with the Flight Attendant was to advise him that we were experiencing pressurization problems and would be descending. I would contact him again when we knew more. As the Aircraft approached 17000 I contacted the Flight Attendant and told him that we were unable to keep the aircraft pressurized and were diverting with a landing in 15 to 20 minutes. I asked him the condition of the cabin crew and passengers and he advised that all were fine and most knew nothing happened until we started our descent. The cabin never completely depressurized however the exact differential is not recalled. As we descended to 13000 ft with a cabin altitude of approximately 8000 ft I made a PA stating that we had experienced a cabin pressure problem and we were diverting for repairs. Normal approach and landing were made. Passengers were deplaned and maintenance met the aircraft to initiate troubleshooting on the pressurization problem. After the passengers were off the aircraft I gathered the cabin team together and again asked if they were alright and if they were aware of any passenger illness or difficulties. I was advised that everyone was 'fine' and no passengers communicated any ill effects. Repairs were made to a loose duct in the right pack bay. The passengers that wanted to continue to our planned destination were boarded and the flight continued with no further pressurization problems.

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.