B737 crew had series of uncommanded yaw inputs in-flight.

Attributes
ACN	470539
Time
Date	200004
Day	Thu
Local Time Of Day	1801 To 2400
Place
State Reference	HI
Altitude	msl single value : 19000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zhn.artcc
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	climbout : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : commercial pilot : atp pilot : cfi pilot : instrument
Experience	flight time last 90 days : 175 flight time total : 15000 flight time type : 9000
ASRS Report	470539
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : landed in emergency condition flight crew : declared emergency other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

After takeoff from koa in a 30 degree bank, aircraft yaw was felt by crew at 800 ft to 1000 ft. Engine checked ok so climb was continued. While passing FL190 we experienced yaw left to right with roll bank angles of 15 degrees to 20 degrees. Disengaged autoplt and started to level off. Hnl center (ATC) advised us we were off course and heading and not climbing to FL230. Captain informed ATC we were experiencing flight control problems. First officer started turn to left on course and oscillations (roll) reoccurred. Captain turned off yaw damper and aircraft continued to oscillate several cycles before it stopped. Captain declared emergency and uneventful landing in hnl. Callback conversation with reporter revealed the following information: crew was flying a B737-200 aircraft. According to the reporter, the aircraft did not have the new yaw damper installed. Even though the yaw damper had been turned off, there was another series of uncommanded yaw inputs. The captain did not have any further information from maintenance.

Original NASA ASRS Text

Title: B737 CREW HAD SERIES OF UNCOMMANDED YAW INPUTS INFLT.

Narrative: AFTER TKOF FROM KOA IN A 30 DEG BANK, ACFT YAW WAS FELT BY CREW AT 800 FT TO 1000 FT. ENG CHECKED OK SO CLB WAS CONTINUED. WHILE PASSING FL190 WE EXPERIENCED YAW L TO R WITH ROLL BANK ANGLES OF 15 DEGS TO 20 DEGS. DISENGAGED AUTOPLT AND STARTED TO LEVEL OFF. HNL CTR (ATC) ADVISED US WE WERE OFF COURSE AND HDG AND NOT CLBING TO FL230. CAPT INFORMED ATC WE WERE EXPERIENCING FLT CTL PROBS. FO STARTED TURN TO L ON COURSE AND OSCILLATIONS (ROLL) REOCCURRED. CAPT TURNED OFF YAW DAMPER AND ACFT CONTINUED TO OSCILLATE SEVERAL CYCLES BEFORE IT STOPPED. CAPT DECLARED EMER AND UNEVENTFUL LNDG IN HNL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CREW WAS FLYING A B737-200 ACFT. ACCORDING TO THE RPTR, THE ACFT DID NOT HAVE THE NEW YAW DAMPER INSTALLED. EVEN THOUGH THE YAW DAMPER HAD BEEN TURNED OFF, THERE WAS ANOTHER SERIES OF UNCOMMANDED YAW INPUTS. THE CAPT DID NOT HAVE ANY FURTHER INFO FROM MAINT.

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.