Narrative:

Cruising at FL400 we heard a loud bang that sounded like it came from the galley. A couple minutes later; the flight attendant called and asked us about the noise. At that time; we noticed the cabin altitude climbing. The altitude warning horn sounded shortly thereafter. I told the flight attendant we would be landing soon. We proceeded with our immediate action items and notified ATC. Once we were given a clearance to descend; we began an emergency descent. I ran the cabin altitude warning checklist. That checklist led us to the emergency descent checklist. We descended the aircraft to below 10;000 ft before taking off our oxygen masks.after descending through 10;000 ft I got a status update from the flight attendant. I also briefed them about our diversion and time until landing. I then briefed the passengers and notified them that they could remove their masks. The first officer remained the pilot flying and did a great job flying and preparing for the landing. We briefed the approach and ran appropriate checklists. As time permitted; we notified ops. After clearing the runway; we had crash fire rescue equipment (crash fire rescue) inspect the aircraft for damage. No visible damage was noted. We taxied to the gate. When we arrived; we had a cabin altitude of approximately 3000 ft. So; I manually depressurized the plane so we could open the door. The aircraft was further inspected by crash fire rescue equipment and was deemed secure.

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Original NASA ASRS Text

Title: Boeing 737-700 Captain reported loss of pressurization.

Narrative: Cruising at FL400 we heard a loud bang that sounded like it came from the galley. A couple minutes later; the Flight Attendant called and asked us about the noise. At that time; we noticed the cabin altitude climbing. The altitude warning horn sounded shortly thereafter. I told the Flight Attendant we would be landing soon. We proceeded with our immediate action items and notified ATC. Once we were given a clearance to descend; we began an emergency descent. I ran the Cabin Altitude Warning checklist. That checklist led us to the Emergency Descent checklist. We descended the aircraft to below 10;000 ft before taking off our oxygen masks.After descending through 10;000 ft I got a status update from the Flight Attendant. I also briefed them about our diversion and time until landing. I then briefed the Passengers and notified them that they could remove their masks. The First Officer remained the Pilot Flying and did a great job flying and preparing for the landing. We briefed the approach and ran appropriate checklists. As time permitted; we notified Ops. After clearing the runway; we had CFR (Crash Fire Rescue) inspect the aircraft for damage. No visible damage was noted. We taxied to the gate. When we arrived; we had a cabin altitude of approximately 3000 ft. So; I manually depressurized the plane so we could open the door. The aircraft was further inspected by CFR and was deemed secure.

Data retrieved from NASA's ASRS site 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.