Flight crew encounters uncommanded yaw oscillation while climbing out of lax.

Attributes
ACN	442873
Time
Date	199907
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : lax.vortac
State Reference	CA
Altitude	msl single value : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 230 flight time total : 9000 flight time type : 5000
ASRS Report	442873
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : landed as precaution flight crew : regained aircraft control
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Uncommanded yaw on climb out passing 6000 ft at 250 KTS. Yaw can be described as rapid side-to-side motion. This event occurred 2 times, lasting 2-3 seconds each time. The yaw damper was shut off and a return to lax was made without incident. Maintenance was advised, and the aircraft was grounded for inspection. ATC was immediately notified and no clearance deviations occurred. Callback conversation with reporter revealed the following information: the reporter confirmed that the aircraft was, in fact, a B737-300. He stated that after turning off the yaw dampers, the oscillation did not recur. He was unable to troubleshoot the system due to his desire to return and land as soon as possible. Maintenance took the aircraft OTS and removed the fdr. They also checked and determined that some but not all of the modifications had been completed. No anomaly was discovered and the aircraft was eventually returned to service. The reporter also mentioned that at the time of the occurrence, the possibility of some WX related control problem never entered his mind.

Original NASA ASRS Text

Title: FLC ENCOUNTERS UNCOMMANDED YAW OSCILLATION WHILE CLBING OUT OF LAX.

Narrative: UNCOMMANDED YAW ON CLBOUT PASSING 6000 FT AT 250 KTS. YAW CAN BE DESCRIBED AS RAPID SIDE-TO-SIDE MOTION. THIS EVENT OCCURRED 2 TIMES, LASTING 2-3 SECONDS EACH TIME. THE YAW DAMPER WAS SHUT OFF AND A RETURN TO LAX WAS MADE WITHOUT INCIDENT. MAINT WAS ADVISED, AND THE ACFT WAS GNDED FOR INSPECTION. ATC WAS IMMEDIATELY NOTIFIED AND NO CLRNC DEVS OCCURRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR CONFIRMED THAT THE ACFT WAS, IN FACT, A B737-300. HE STATED THAT AFTER TURNING OFF THE YAW DAMPERS, THE OSCILLATION DID NOT RECUR. HE WAS UNABLE TO TROUBLESHOOT THE SYS DUE TO HIS DESIRE TO RETURN AND LAND ASAP. MAINT TOOK THE ACFT OTS AND REMOVED THE FDR. THEY ALSO CHKED AND DETERMINED THAT SOME BUT NOT ALL OF THE MODIFICATIONS HAD BEEN COMPLETED. NO ANOMALY WAS DISCOVERED AND THE ACFT WAS EVENTUALLY RETURNED TO SVC. THE RPTR ALSO MENTIONED THAT AT THE TIME OF THE OCCURRENCE, THE POSSIBILITY OF SOME WX RELATED CTL PROB NEVER ENTERED HIS MIND.

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.