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B737-300 flight crew experiences an autopilot malfunction at FL370 that commences with a pitch up then pitch down. The autopilot is disconnected using the yoke switch but continues to pitch down. Brute force is used to overpower and disengage the autopilot and return the aircraft to FL370. A previous identical malfunction had been signed off by maintenance as 'bite check ok'.
| Attributes | |
| ACN | 960841 |
| Time | |
| Date | 201107 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Autopilot |
| Person 1 | |
| Function | Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 239 Flight Crew Type 11200 |
| Person 2 | |
| Function | First Officer |
| Experience | Flight Crew Last 90 Days 155 Flight Crew Type 3500 |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude |
Narrative:
Cruising at FL370; the autopilot initially climbed and then descended at approximately 1;500 FPM. The pilot flying hit the autopilot disconnect switch on the yoke; the horn sounded; but autopilot did not disengage. The pilot not flying had to use extreme force to override and disengage the autopilot. This was an exact copy of the previous discrepancy on the aircraft's last flight. Write-up was; 'ran bite check no faults found.
Original NASA ASRS Text
Title: B737-300 flight crew experiences an autopilot malfunction at FL370 that commences with a pitch up then pitch down. The autopilot is disconnected using the yoke switch but continues to pitch down. Brute force is used to overpower and disengage the autopilot and return the aircraft to FL370. A previous identical malfunction had been signed off by maintenance as 'bite check OK'.
Narrative: Cruising at FL370; the autopilot initially climbed and then descended at approximately 1;500 FPM. The pilot flying hit the autopilot disconnect switch on the yoke; the horn sounded; but autopilot did not disengage. The pilot not flying had to use extreme force to override and disengage the autopilot. This was an exact copy of the previous discrepancy on the aircraft's last flight. Write-up was; 'Ran bite check no faults found.
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.