Narrative:

During cruise at FL430 with the autopilot engaged the aircraft began vibrating accompanied by a 'pitch feel' light on the annunciator panel and overspeed indications the airspeed indicator. I disengaged the autopilot and began reducing power for what initially looked and felt like a severe overspeed. After reducing power and noting the vibrations were not decreasing and realizing that I was going to be unable to maintain altitude I asked the pilot monitoring to advise ATC that we needed to vacate our altitude. As I began the descent I noticed that the green slat extended light on the forward panel was illuminated. I immediately directed my attention to the slat/flap handle and noticed that it was not securely seated in the clean detent; however it had not moved completely to the ten degree detent. I called for the slat handle to be moved to the clean position and continued a descent while waiting to see if the slats and flaps would retract. Descending through approximately FL422 the retraction sequence completed and I began a slow lower power climb back to FL430 while verifying that no additional control problems existed. After reaching FL430 and discussing the situation with our maintenance department the decision was made to return and have the aircraft inspected. The flight returned without further incident.

Related reports:

Google
 

Original NASA ASRS Text

Title: DA2000 First Officer experienced vibration and overspeed warnings at FL430. The autopilot was disengaged and thrust reduced before a slat light was observed on the forward panel. The flap handle was then discovered out of the clean detent and when corrected the slats retract. Flight diverted for maintenance inspection.

Narrative: During cruise at FL430 with the autopilot engaged the aircraft began vibrating accompanied by a 'Pitch Feel' light on the annunciator panel and overspeed indications the airspeed indicator. I disengaged the autopilot and began reducing power for what initially looked and felt like a severe overspeed. After reducing power and noting the vibrations were not decreasing and realizing that I was going to be unable to maintain altitude I asked the pilot monitoring to advise ATC that we needed to vacate our altitude. As I began the descent I noticed that the green slat extended light on the forward panel was illuminated. I immediately directed my attention to the slat/flap handle and noticed that it was not securely seated in the clean detent; however it had not moved completely to the ten degree detent. I called for the slat handle to be moved to the clean position and continued a descent while waiting to see if the slats and flaps would retract. Descending through approximately FL422 the retraction sequence completed and I began a slow lower power climb back to FL430 while verifying that no additional control problems existed. After reaching FL430 and discussing the situation with our maintenance department the decision was made to return and have the aircraft inspected. The flight returned without further incident.

Data retrieved from NASA's ASRS site as of April 2012 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.