Narrative:

While climbing out we encountered heavy vibration. The flight attendant from the aft position called to confirm the vibration and was very concerned. We have a full complement of passengers--99. At that time; we were climbing through 24000 ft and cleared to 31000 ft. Almost immediately; the first officer pointed out the cabin altitude on the EICAS display. The cabin was 8600 ft and climbing; and was surrounded by an amber box. We made a call to ATC to stop our climb and did at FL250. The cabin stabilized at 10300 ft. We declared an emergency with ATC and descended to 21000 ft; then after clearing traffic; down to 15000 ft. The cabin descended below 10000 ft. Both pilots put their masks on when the cabin was above 10000 ft but after descending through around 23000 ft; the cabin descended to 9700 ft. We removed our masks. I assigned the flying duties to the first officer; referenced the QRH; and made a decision to divert. The aircraft continued to shake and vibrate and we slowed the speed down to 250 knots. The vibration subsided somewhat; but it was clear and we believed we had some sort of structural failure. I also referenced the QRH on this issue. After slowing the vibration did diminish; and we had no abnormal indications in the fightdeck. All engine and system parameters were indicating normal; except the cabin altitude was not able to pressurize to its full extent. My belief was a door or panel was cracked open enough to create a hole in the aircraft; but not give us any indication. The vibration was very apparent and was not normal. We landed in uneventfully; and had emergency equipment standing by as a precaution; since we believed there was something wrong structurally with the aircraft. After a normal landing; we taxied to a gate and met with maintenance. We subsequently called maintenance the next day and learned that the ducting had detached from the air cycle machine. This created another hole in the pressurized vessel and also the very strong vibration throughout the aircraft. Apparently; this has happened before; and there is no indication of this in the cockpit. I would suggest revising the QRH and putting the checklists for structural and rapid decompression in close proximity to each other with some options. This did not require an emergency descent because we were low enough to catch it and the cabin was still pressurizing to a degree. Early detection is key to pressurization problems. Also; I would add some guidance for severe vibration with language to land at nearest suitable airport!

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Original NASA ASRS Text

Title: An EMB190's air conditioning duct detached from an air cycle machine causing an airframe vibration and the partial loss of pressurization. An emergency was declared and the flight diverted to an enroute airport.

Narrative: While climbing out we encountered heavy vibration. The flight attendant from the aft position called to confirm the vibration and was very concerned. We have a full complement of passengers--99. At that time; we were climbing through 24000 ft and cleared to 31000 ft. Almost immediately; the First Officer pointed out the cabin altitude on the EICAS display. The cabin was 8600 ft and climbing; and was surrounded by an amber box. We made a call to ATC to stop our climb and did at FL250. The cabin stabilized at 10300 ft. We declared an emergency with ATC and descended to 21000 ft; then after clearing traffic; down to 15000 ft. The cabin descended below 10000 ft. Both Pilots put their masks on when the cabin was above 10000 ft but after descending through around 23000 ft; the cabin descended to 9700 ft. We removed our masks. I assigned the flying duties to the First Officer; referenced the QRH; and made a decision to divert. The aircraft continued to shake and vibrate and we slowed the speed down to 250 knots. The vibration subsided somewhat; but it was clear and we believed we had some sort of structural failure. I also referenced the QRH on this issue. After slowing the vibration did diminish; and we had NO ABNORMAL INDICATIONS IN THE FIGHTDECK. All engine and system parameters were indicating normal; except the cabin altitude was not able to pressurize to its full extent. My belief was a door or panel was cracked open enough to create a hole in the aircraft; but not give us any indication. The vibration was very apparent and was not normal. We landed in uneventfully; and had emergency equipment standing by as a precaution; since we believed there was something wrong structurally with the aircraft. After a normal landing; we taxied to a gate and met with maintenance. We subsequently called maintenance the next day and learned that the ducting had detached from the air cycle machine. This created another hole in the pressurized vessel and also the very strong vibration throughout the aircraft. Apparently; this has happened before; and there is no indication of this in the cockpit. I would suggest revising the QRH and putting the checklists for structural and rapid decompression in close proximity to each other with some options. This did not require an emergency descent because we were low enough to catch it and the cabin was still pressurizing to a degree. Early detection is key to pressurization problems. Also; I would add some guidance for severe vibration with language to LAND AT NEAREST SUITABLE AIRPORT!

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.