BE40 crew reported moderate turbulence encounter that caused dutch roll action and loss of control o...

Attributes
ACN	1425015
Time
Date	201702
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Beechjet 400
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 2450 Flight Crew Type 1600
Person 2
Function	Pilot Not Flying
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 5700 Flight Crew Type 1260
Events
Anomaly	Inflight Event / Encounter Loss Of Aircraft Control Inflight Event / Encounter Weather / Turbulence

Narrative:

We were in level cruise at FL380 after departing for ZZZ. At approximately XA35 we began to encounter what we referred to as 'light chop occasional moderate chop'. Shortly thereafter; the aircraft began to dutch roll. Autopilot and yaw damper remained engaged with no indications of any equipment failure. The dutch roll got progressively worse; and the pilot not flying; disconnected the autopilot in an attempt to help me; the pilot flying; in regaining control of the airplane. We were still unable to regain control of the aircraft with the autopilot disconnected and the pilot not flying then [advised ATC] to begin a descent. Somewhere below FL370 we were able to get the airplane stabilized and we requested to level off at FL360 to assess the situation; the aircraft; and the passengers. We still had no indications of any equipment failures at that time. Upon our assessment that the airplane and passengers were ok; we noticed that we had flown through an inversion; as the wind had shifted at least 90 degrees in direction. Based on that; and the fact that we had no indications of any failures; I re-engaged the autopilot successfully and we requested a turn direct to ZZZ where we landed without further incident.

Original NASA ASRS Text

Title: BE40 crew reported moderate turbulence encounter that caused dutch roll action and loss of control of aircraft. Flight crew was able to descend to a lower altitude out of turbulence/windshear and regain control of aircraft.

Narrative: We were in level cruise at FL380 after departing for ZZZ. At approximately XA35 we began to encounter what we referred to as 'light chop occasional moderate chop'. Shortly thereafter; the aircraft began to Dutch roll. Autopilot and Yaw Damper remained engaged with no indications of any equipment failure. The Dutch roll got progressively worse; and the pilot not flying; disconnected the autopilot in an attempt to help me; the pilot flying; in regaining control of the airplane. We were still unable to regain control of the aircraft with the autopilot disconnected and the pilot not flying then [advised ATC] to begin a descent. Somewhere below FL370 we were able to get the airplane stabilized and we requested to level off at FL360 to assess the situation; the aircraft; and the passengers. We still had no indications of any equipment failures at that time. Upon our assessment that the airplane and passengers were ok; we noticed that we had flown through an inversion; as the wind had shifted at least 90 degrees in direction. Based on that; and the fact that we had no indications of any failures; I re-engaged the autopilot successfully and we requested a turn direct to ZZZ where we landed without further incident.

Data retrieved from NASA's ASRS site 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.