|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1801 To 2400|
|Locale Reference||airport : zzz.airport|
|Altitude||msl single value : 14000|
|Controlling Facilities||tracon : zzz.tracon|
|Operator||common carrier : air carrier|
|Make Model Name||MD-88|
|Operating Under FAR Part||Part 121|
|Navigation In Use||other|
|Flight Phase||climbout : intermediate altitude|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
|Experience||flight time last 90 days : 120|
flight time total : 8000
flight time type : 2000
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Anomaly||aircraft equipment problem : critical|
other anomaly other
|Independent Detector||other flight crewa|
other flight crewb
|Resolutory Action||flight crew : diverted to another airport|
|Problem Areas||Environmental Factor|
Flight Crew Human Performance
Captain's leg. After takeoff and through clean-up altitude, aircraft experienced what felt like wake turbulence, accompanied by steady requirement for aileron displacement to the left, then right to hold wing's level. A little more than a unit of trim took off the pressure in both directions. As aircraft accelerated through clean speed, all felt normal, and aileron trim was reset to zero degrees. Autoplt #1 was engaged, and all felt normal. Approximately 9000 ft. 250 KIAS a continuous rudder oscillation of approximately 1 cycle per second began abruptly, of light, but steady intensity. Yaw damper was verified on. No caution lights were illuminated. Autoplt was disconnected to no effect and re-engaged. I continued climb to a troubleshooting altitude of 14000 ft and 280 KIAS. First officer initiated the 'aircraft oscillating or displaced in yaw' checklist. Swapped to autoplt #2 to no initial effect. Then after several seconds oscillation dissipated away. Autoplt #2 was engaged, climb out acceleration was commenced. Approximately 310 KIAS oscillation abruptly returned. I leveled and slowed towards 250 KIAS. Checklist was continued, and rudder hydraulic control was selected to manual. Oscillation again dissipated. Checklist was again suspended as oscillation ceased. Although I credited the ceasing of oscillation to the reduction in speed. I elected to keep rudder in manual for remainder of flight. Elected to return to ZZZ for landing. Night VFR landing was made with no further problems. Did not declare an emergency. Callback conversation with reporter revealed the following information: the reporter stated the cause of the rudder oscillation is unknown as maintenance has not reported the action taken or the malfunctioning component. The reporter said flight manual procedures will not allow disconnecting the yaw damper for troubleshooting.
Original NASA ASRS Text
Title: AN MD88 IN CLB EXPERIENCED A YAW OSCILLATION OF 1 CYCLE PER SECOND. NO CAUTION LIGHTS AND AUTOPLTS SWITCHED NO HELP. YAW DAMPER NOT SWITCHED OFF.
Narrative: CAPT'S LEG. AFTER TKOF AND THROUGH CLEAN-UP ALT, ACFT EXPERIENCED WHAT FELT LIKE WAKE TURB, ACCOMPANIED BY STEADY REQUIREMENT FOR AILERON DISPLACEMENT TO THE L, THEN R TO HOLD WING'S LEVEL. A LITTLE MORE THAN A UNIT OF TRIM TOOK OFF THE PRESSURE IN BOTH DIRECTIONS. AS ACFT ACCELERATED THROUGH CLEAN SPD, ALL FELT NORMAL, AND AILERON TRIM WAS RESET TO ZERO DEGS. AUTOPLT #1 WAS ENGAGED, AND ALL FELT NORMAL. APPROX 9000 FT. 250 KIAS A CONTINUOUS RUDDER OSCILLATION OF APPROX 1 CYCLE PER SECOND BEGAN ABRUPTLY, OF LIGHT, BUT STEADY INTENSITY. YAW DAMPER WAS VERIFIED ON. NO CAUTION LIGHTS WERE ILLUMINATED. AUTOPLT WAS DISCONNECTED TO NO EFFECT AND RE-ENGAGED. I CONTINUED CLB TO A TROUBLESHOOTING ALT OF 14000 FT AND 280 KIAS. FO INITIATED THE 'ACFT OSCILLATING OR DISPLACED IN YAW' CHKLIST. SWAPPED TO AUTOPLT #2 TO NO INITIAL EFFECT. THEN AFTER SEVERAL SECONDS OSCILLATION DISSIPATED AWAY. AUTOPLT #2 WAS ENGAGED, CLBOUT ACCELERATION WAS COMMENCED. APPROX 310 KIAS OSCILLATION ABRUPTLY RETURNED. I LEVELED AND SLOWED TOWARDS 250 KIAS. CHKLIST WAS CONTINUED, AND RUDDER HYD CTL WAS SELECTED TO MANUAL. OSCILLATION AGAIN DISSIPATED. CHKLIST WAS AGAIN SUSPENDED AS OSCILLATION CEASED. ALTHOUGH I CREDITED THE CEASING OF OSCILLATION TO THE REDUCTION IN SPD. I ELECTED TO KEEP RUDDER IN MANUAL FOR REMAINDER OF FLT. ELECTED TO RETURN TO ZZZ FOR LNDG. NIGHT VFR LNDG WAS MADE WITH NO FURTHER PROBS. DID NOT DECLARE AN EMER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE RUDDER OSCILLATION IS UNKNOWN AS MAINT HAS NOT RPTED THE ACTION TAKEN OR THE MALFUNCTIONING COMPONENT. THE RPTR SAID FLT MANUAL PROCS WILL NOT ALLOW DISCONNECTING THE YAW DAMPER FOR TROUBLESHOOTING.
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.