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B737's out-of-limits yaw damper coupler caused uncommanded yaw during descent. Aircraft equipment problem yaw damper system.
| Attributes | |
| ACN | 321064 |
| Time | |
| Date | 199511 |
| Day | Thu |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : lga |
| State Reference | NY |
| Altitude | msl bound lower : 7000 msl bound upper : 7000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : n90 |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | descent : approach descent other landing other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : cfi pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 12000 flight time type : 1200 |
| ASRS Report | 321064 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp pilot : cfi pilot : flight engineer |
| Experience | flight time last 90 days : 180 flight time total : 14000 flight time type : 4000 |
| ASRS Report | 320668 |
| Events | |
| Anomaly | aircraft equipment problem : less severe |
| Independent Detector | other flight crewa |
| Resolutory Action | none taken : detected after the fact other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
On approach to lga, 7000 ft, and 210 KTS clean, experienced uncommanded yaw. Maximum turn 20 degrees. Captain turned off autoplt and yaw damper, and landed at lga runway 31. Callback conversation with reporter revealed the following information: reporter recently received a letter from the company accident investigator stating that the uncommanded yaw was the result of an out-of-limits yaw damper coupler. The first officer (reporter) states that after the B737-300 yawed to the left, the autoplt attempted to compensate with a roll (control wheel was 45 degree right) back to wings level. He immediately recognized that this was a yaw damper problem because the yaw damper indicator was displaced completely to the right. When the yaw damper was turned off, the indication came back to center. The uncommanded yaw and the subsequent efforts to correct the situation were abrupt enough to throw 2 flight attendants onto the cabin floor.
Original NASA ASRS Text
Title: B737'S OUT-OF-LIMITS YAW DAMPER COUPLER CAUSED UNCOMMANDED YAW DURING DSCNT. ACFT EQUIP PROB YAW DAMPER SYS.
Narrative: ON APCH TO LGA, 7000 FT, AND 210 KTS CLEAN, EXPERIENCED UNCOMMANDED YAW. MAX TURN 20 DEGS. CAPT TURNED OFF AUTOPLT AND YAW DAMPER, AND LANDED AT LGA RWY 31. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR RECENTLY RECEIVED A LETTER FROM THE COMPANY ACCIDENT INVESTIGATOR STATING THAT THE UNCOMMANDED YAW WAS THE RESULT OF AN OUT-OF-LIMITS YAW DAMPER COUPLER. THE FO (RPTR) STATES THAT AFTER THE B737-300 YAWED TO THE L, THE AUTOPLT ATTEMPTED TO COMPENSATE WITH A ROLL (CTL WHEEL WAS 45 DEG R) BACK TO WINGS LEVEL. HE IMMEDIATELY RECOGNIZED THAT THIS WAS A YAW DAMPER PROB BECAUSE THE YAW DAMPER INDICATOR WAS DISPLACED COMPLETELY TO THE R. WHEN THE YAW DAMPER WAS TURNED OFF, THE INDICATION CAME BACK TO CTR. THE UNCOMMANDED YAW AND THE SUBSEQUENT EFFORTS TO CORRECT THE SIT WERE ABRUPT ENOUGH TO THROW 2 FLT ATTENDANTS ONTO THE CABIN FLOOR.
Data retrieved from NASA's ASRS site as of July 2007 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.