A BE90 at FL250 abruptly banked 30-40 degrees and descended 500 ft-600 ft as the pilot was turned to...

Attributes
ACN	954238
Time
Date	201106
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	King Air C90 E90
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 4450 Flight Crew Type 1500
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

In cruise at FL250; autopilot on; I turned around to answer a question from the passengers in the back of the plane. As I was speaking with them the aircraft banked 30-40 degrees to the right and started an abrupt decent. I turned around to see what was happening and immediately pushed the autopilot/yd disconnect and corrected the aircraft altitude and heading and in that process made a proactive radio call to ATC to let them know something had happened and that I was correcting the issue. I informed them that no assistance was required at that time; and that I would call them back in a little bit to verify that all was ok. This gave me a chance to try and identify the problem. The aircraft had lost between 500-600 ft during this abrupt decent and had changed heading roughly 60 degrees. This aircraft is equipped with the G1000 package and a garmin autopilot. Because I hit the autopilot disconnect so quickly; in order to correct the aircraft's attitude; I am still unsure if it was an autopilot malfunction or a trim runaway. There were no conflicts with other aircraft.

Original NASA ASRS Text

Title: A BE90 at FL250 abruptly banked 30-40 degrees and descended 500 FT-600 FT as the pilot was turned to address passengers. The upset's cause is unknown.

Narrative: In cruise at FL250; autopilot on; I turned around to answer a question from the passengers in the back of the plane. As I was speaking with them the aircraft banked 30-40 degrees to the right and started an abrupt decent. I turned around to see what was happening and immediately pushed the Autopilot/YD Disconnect and corrected the aircraft altitude and heading and in that process made a proactive radio call to ATC to let them know something had happened and that I was correcting the issue. I informed them that no assistance was required at that time; and that I would call them back in a little bit to verify that all was OK. This gave me a chance to try and identify the problem. The aircraft had lost between 500-600 FT during this abrupt decent and had changed heading roughly 60 degrees. This aircraft is equipped with the G1000 package and a Garmin Autopilot. Because I hit the autopilot disconnect so quickly; in order to correct the aircraft's attitude; I am still unsure if it was an autopilot malfunction or a trim runaway. There were no conflicts with other aircraft.

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.

A BE90 at FL250 abruptly banked 30-40 degrees and descended 500 ft-600 ft as the pilot was turned to address passengers. The upset's cause is unknown.