Narrative:

We had just leveled off at FL370 for approximately two minutes when we noticed our ears popping. We looked at the cabin pressure gauge and noticed the cabin rate was climbing at approximately 1;800 fpm and the cabin altitude was slowly climbing as well. At about that time; the flight attendant called the flight deck to ask if we heard a noise. Over the interphone we could hear a whining noise and could still feel our ears popping with the cabin climb rate still climbing at 1;800 fpm. We donned our oxygen masks; established communications with each other; and pulled out the QRH and referenced the cabin altitude warning/abnormal pressurization checklist. We declared an emergency with center and coordinated an emergency descent down to 11;000 feet MSL and requested routing back to [departure airport]. As we descended; we continued in the checklist to completion. We requested a descent to 10;000 feet MSL so that we could remove our oxygen masks and continue to assess our situation. At 10;000 feet MSL; cabin pressurization had returned to normal so we removed our oxygen masks and discussed our options including returning to [departure airport]. The captain communicated with the flight attendants and passengers. We concluded that since the pressurization was under control and after confirming with the flight attendants that there was no obvious damage in the cabin that caused the depressurization that the best course of action would be to return while burning off fuel to avoid an overweight landing. We notified dispatch of our intentions; ensured that all checklists were completed; and communications were covered. After approximately one hour of holding; we returned and landed uneventfully and conducted a normal taxi to the gate. As we are still unclear what actually caused the depressurization; we can't speculate if there was anyone responsible for the incident or determine if there was any way to prevent it.

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Original NASA ASRS Text

Title: B737-700 flight crew reported loss of cabin pressure shortly after reaching cruise altitude of FL370. They declared an emergency; descended; and returned to departure airport.

Narrative: We had just leveled off at FL370 for approximately two minutes when we noticed our ears popping. We looked at the cabin pressure gauge and noticed the cabin rate was climbing at approximately 1;800 fpm and the cabin altitude was slowly climbing as well. At about that time; the Flight Attendant called the flight deck to ask if we heard a noise. Over the interphone we could hear a whining noise and could still feel our ears popping with the cabin climb rate still climbing at 1;800 fpm. We donned our oxygen masks; established communications with each other; and pulled out the QRH and referenced the Cabin Altitude Warning/Abnormal Pressurization Checklist. We declared an emergency with Center and coordinated an emergency descent down to 11;000 feet MSL and requested routing back to [departure airport]. As we descended; we continued in the checklist to completion. We requested a descent to 10;000 feet MSL so that we could remove our oxygen masks and continue to assess our situation. At 10;000 feet MSL; cabin pressurization had returned to normal so we removed our oxygen masks and discussed our options including returning to [departure airport]. The Captain communicated with the flight attendants and passengers. We concluded that since the pressurization was under control and after confirming with the flight attendants that there was no obvious damage in the cabin that caused the depressurization that the best course of action would be to return while burning off fuel to avoid an overweight landing. We notified Dispatch of our intentions; ensured that all checklists were completed; and communications were covered. After approximately one hour of holding; we returned and landed uneventfully and conducted a normal taxi to the gate. As we are still unclear what actually caused the depressurization; we can't speculate if there was anyone responsible for the incident or determine if there was any way to prevent it.

Data retrieved from NASA's ASRS site as of July 2013 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.