Narrative:

In the early portion of our arrival descent, the control column moved aft abruptly 1 1/2 inches or less with no corresponding pitch up motion of the aircraft. The control column had also moved in the roll motion 1/2 inch with no aircraft roll. Both occurred with autoplt 'a' in use. The pitch motion was more noticeable and though others have experienced this and a vertical gyroscope was usually at fault, I didn't believe either motion was pronounced enough and because of the pitch and no commanded roll or yaw occurred, I did not properly diagnose the situation. In light of previous B737 autoplt related uncommanded rolls and yaws, I should have tried the vertical gyroscope 'captain on auxiliary' setting on the selector knob, and therefore I would have eliminated the remote possibility of an uncommanded roll/yaw if the two had been related. Callback conversation with reporter revealed the following information: reporter says the primary focus of submitting the report was a result of the extra attention given to the B737-200 controllability questions. The control column movement was not extreme, but reporter thought it was more movement than usual. He suspected the vertical gyroscope was causing the excess movement and says that he should have checked the autoplt operations on the auxiliary gyroscope. Feedback from his company was that it was non-event, but thanked him for the report.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB. VERT GYROSCOPE CAUSING AUTOPLT OSCILLATION.

Narrative: IN THE EARLY PORTION OF OUR ARR DSCNT, THE CTL COLUMN MOVED AFT ABRUPTLY 1 1/2 INCHES OR LESS WITH NO CORRESPONDING PITCH UP MOTION OF THE ACFT. THE CTL COLUMN HAD ALSO MOVED IN THE ROLL MOTION 1/2 INCH WITH NO ACFT ROLL. BOTH OCCURRED WITH AUTOPLT 'A' IN USE. THE PITCH MOTION WAS MORE NOTICEABLE AND THOUGH OTHERS HAVE EXPERIENCED THIS AND A VERT GYROSCOPE WAS USUALLY AT FAULT, I DIDN'T BELIEVE EITHER MOTION WAS PRONOUNCED ENOUGH AND BECAUSE OF THE PITCH AND NO COMMANDED ROLL OR YAW OCCURRED, I DID NOT PROPERLY DIAGNOSE THE SIT. IN LIGHT OF PREVIOUS B737 AUTOPLT RELATED UNCOMMANDED ROLLS AND YAWS, I SHOULD HAVE TRIED THE VERT GYROSCOPE 'CAPT ON AUX' SETTING ON THE SELECTOR KNOB, AND THEREFORE I WOULD HAVE ELIMINATED THE REMOTE POSSIBILITY OF AN UNCOMMANDED ROLL/YAW IF THE TWO HAD BEEN RELATED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAYS THE PRIMARY FOCUS OF SUBMITTING THE RPT WAS A RESULT OF THE EXTRA ATTENTION GIVEN TO THE B737-200 CONTROLLABILITY QUESTIONS. THE CTL COLUMN MOVEMENT WAS NOT EXTREME, BUT RPTR THOUGHT IT WAS MORE MOVEMENT THAN USUAL. HE SUSPECTED THE VERT GYROSCOPE WAS CAUSING THE EXCESS MOVEMENT AND SAYS THAT HE SHOULD HAVE CHKED THE AUTOPLT OPS ON THE AUX GYROSCOPE. FEEDBACK FROM HIS COMPANY WAS THAT IT WAS NON-EVENT, BUT THANKED HIM FOR THE RPT.

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.