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Pilot reports that shortly after initiating descent from FL400; he noticed the cabin altitude climbing at 1;500 FPM on their next gen B737-700 aircraft. Before the cabin altitude exceeded 10;000 ft; the aircraft leveled off at FL360 with an increase in thrust that immediately restored control of the cabin. Maintenance found a loose clamp in aft pressure bulkhead.
| Attributes | |
| ACN | 1168166 |
| Time | |
| Date | 201404 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Pressurization System |
| Person 1 | |
| Function | First Officer Pilot Not Flying |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Inflight Event / Encounter Other / Unknown |
Narrative:
B737-700 aircraft; in cruise at FL400; center directed a descent to FL360. Shortly after initiating the descent; I noticed the cabin altitude climbing at 1;500 FPM. The captain and I began scanning for reasons for this loss of pressurization; however all indications seemed normal (bleed pointers sensed; outflow valve closed; pressurization controller in alternate per MEL). I donned my mask in anticipation of receiving the cabin altitude (alt) horn and got the QRH ready. Before the cabin exceeded 10;000 ft; the aircraft leveled off at our assigned altitude of FL360. The resulting increase in thrust immediately restored control of our cabin. We asked ATC for a constant descent at a reduced rate so that we could keep thrust on the engines; and had an uneventful approach and landing. The altitude warning horn never went off. Maintenance later identified the cause of the failure to be a loose clamp in the aft pressure bulkhead. System malfunction.
Original NASA ASRS Text
Title: Pilot reports that shortly after initiating descent from FL400; he noticed the cabin altitude climbing at 1;500 FPM on their Next Gen B737-700 aircraft. Before the cabin altitude exceeded 10;000 FT; the aircraft leveled off at FL360 with an increase in thrust that immediately restored control of the cabin. Maintenance found a loose clamp in aft pressure bulkhead.
Narrative: B737-700 aircraft; in cruise at FL400; Center directed a descent to FL360. Shortly after initiating the descent; I noticed the cabin altitude climbing at 1;500 FPM. The Captain and I began scanning for reasons for this loss of pressurization; however all indications seemed normal (Bleed pointers sensed; outflow valve closed; pressurization controller in alternate per MEL). I donned my mask in anticipation of receiving the Cabin Altitude (Alt) Horn and got the QRH ready. Before the cabin exceeded 10;000 FT; the aircraft leveled off at our assigned altitude of FL360. The resulting increase in thrust immediately restored control of our cabin. We asked ATC for a constant descent at a reduced rate so that we could keep thrust on the engines; and had an uneventful approach and landing. The ALT Warning horn never went off. Maintenance later identified the cause of the failure to be a loose clamp in the AFT pressure bulkhead. System malfunction.
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.