SJ30 yaw damper failed; disconnecting autopilot and resulting in roll and yaw oscillations. Flight c...

Attributes
ACN	742914
Time
Date	200706
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : hsv.airport
State Reference	AL
Altitude	msl single value : 45000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc
Operator	general aviation : personal
Make Model Name	Small Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 15700 flight time type : 80
ASRS Report	742914
Events
Anomaly	aircraft equipment problem : critical other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : provided flight assist flight crew : exited adverse environment
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

At FL490; 150 NM northeast of huntsville; al; the autoplt disconnected. I immediately took manual control of aircraft looking at the annunciator panel noting the yaw damper light illuminated; which indicates a dual channel failure. I notified ZME that we would need to descend immediately. The airplane rolled approximately 30 degrees to the left then back to the right. At the same time the nose yawed in both directions. I immediately eased back the throttles; slowed the airplane and simultaneously started a slow descent. We experienced 3 more roll and yaw oscillations; each one of less roll and yaw in amplitude. Eventually as we descended through approximately FL350 all oscillations ceased. The checklist referred us to resetting the yaw damper circuit breakers. The first reset did not correct the problem; the second reset a few mins later reset the system. We landed uneventfully at huntsville. We did not declare an emergency; but ZME gave us special handling to descend and circumnav large thunderstorms in the immediate area. The situation was reported to maintenance.

Original NASA ASRS Text

Title: SJ30 YAW DAMPER FAILED; DISCONNECTING AUTOPILOT AND RESULTING IN ROLL AND YAW OSCILLATIONS. FLT CREW SLOWED ACFT AND INITIATED A DESCENT WHICH ELIMINATED THE OSCILLATIONS.

Narrative: AT FL490; 150 NM NE OF HUNTSVILLE; AL; THE AUTOPLT DISCONNECTED. I IMMEDIATELY TOOK MANUAL CTL OF ACFT LOOKING AT THE ANNUNCIATOR PANEL NOTING THE YAW DAMPER LIGHT ILLUMINATED; WHICH INDICATES A DUAL CHANNEL FAILURE. I NOTIFIED ZME THAT WE WOULD NEED TO DSND IMMEDIATELY. THE AIRPLANE ROLLED APPROX 30 DEGS TO THE L THEN BACK TO THE R. AT THE SAME TIME THE NOSE YAWED IN BOTH DIRECTIONS. I IMMEDIATELY EASED BACK THE THROTTLES; SLOWED THE AIRPLANE AND SIMULTANEOUSLY STARTED A SLOW DSCNT. WE EXPERIENCED 3 MORE ROLL AND YAW OSCILLATIONS; EACH ONE OF LESS ROLL AND YAW IN AMPLITUDE. EVENTUALLY AS WE DSNDED THROUGH APPROX FL350 ALL OSCILLATIONS CEASED. THE CHKLIST REFERRED US TO RESETTING THE YAW DAMPER CIRCUIT BREAKERS. THE FIRST RESET DID NOT CORRECT THE PROB; THE SECOND RESET A FEW MINS LATER RESET THE SYS. WE LANDED UNEVENTFULLY AT HUNTSVILLE. WE DID NOT DECLARE AN EMER; BUT ZME GAVE US SPECIAL HANDLING TO DSND AND CIRCUMNAV LARGE TSTMS IN THE IMMEDIATE AREA. THE SIT WAS RPTED TO MAINT.

Data retrieved from NASA's ASRS site as of January 2009 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.

SJ30 yaw damper failed; disconnecting autopilot and resulting in roll and yaw oscillations. Flight crew slowed aircraft and initiated a descent which eliminated the oscillations.