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B737 flight crew reports cabin altitude fluctuations at FL370. Crew begins descent with oxygen masks on and regains control of pressurization by selecting alternate controller. Crew elects to divert and declare an emergency.
| Attributes | |
| ACN | 818888 |
| Time | |
| Date | 200901 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Pressurization Control System |
| Person 1 | |
| Function | Captain |
| Person 2 | |
| Function | First Officer |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe |
Narrative:
During cruise flight at FL370; after descending from FL390 due to turbulence; radical pressurization fluctuations encountered. The decision was made to descend to a safe altitude with oxygen masks donned as a precaution. Quick reference checklist and quick reference handbook checklists were followed during initial descent and control of cabin pressurization regained upon selection of the 'alternate' mode of pressurization mode selector (approximately mid descent). An emergency was declared with ATC to assure traffic priority during our unplanned descent in mountainous terrain. Oxygen masks did not deploy in passenger cabin and flight attendants/passengers were briefed of our intentions to divert to ZZZ for maintenance. Once VMC and level at 12;000 ft MSL; we coordinated for the subsequent uneventful descent; approach and landing at ZZZ. This was an unpredictable system abnormality/malfunction.
Original NASA ASRS Text
Title: B737 flight crew reports cabin altitude fluctuations at FL370. Crew begins descent with oxygen masks on and regains control of pressurization by selecting alternate controller. Crew elects to divert and declare an emergency.
Narrative: During cruise flight at FL370; after descending from FL390 due to turbulence; radical pressurization fluctuations encountered. The decision was made to descend to a safe altitude with oxygen masks donned as a precaution. Quick Reference Checklist and Quick Reference Handbook checklists were followed during initial descent and control of cabin pressurization regained upon selection of the 'Alternate' mode of pressurization mode selector (approximately mid descent). An emergency was declared with ATC to assure traffic priority during our unplanned descent in mountainous terrain. Oxygen masks did not deploy in passenger cabin and Flight Attendants/passengers were briefed of our intentions to divert to ZZZ for maintenance. Once VMC and level at 12;000 FT MSL; we coordinated for the subsequent uneventful descent; approach and landing at ZZZ. This was an unpredictable system abnormality/malfunction.
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.