The flight crew of a king air was unable to disconnect the autopilot when it failed to level at thei...

Attributes
ACN	971435
Time
Date	201109
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	King Air C90 E90
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 60 Flight Crew Total 10000 Flight Crew Type 1000
Person 2
Function	Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 5200 Flight Crew Type 10
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Overshoot Deviation - Procedural Clearance Inflight Event / Encounter Loss Of Aircraft Control

Narrative:

As we approached our destination we were given an initial descent and then a continuing descent to 4;000 ft. I was looking at the approach plate for the expected approach when I looked at the altitude and noticed that the rate of descent was not slowing to capture our cleared altitude. I said something to the pilot flying and he pressed the disconnect for the autopilot. At the time we thought the autopilot disconnected. As he tried to pull back on the controls; I noticed the trim start to move. I thought we had a problem with the trim. At this time we descended through our assigned altitude. I advised ATC we had a problem and to standby. We continued to descend slightly below 3;000 ft with both of us trying to override the trim. I then noticed the autopilot had not disconnected. We both tried to disconnect without success and the other pilot tried the pedestal disconnect without success. I then pulled the circuit breaker for the autopilot and at that time we regained control of the aircraft and advised ATC we had the situation under control and could continue.

Original NASA ASRS Text

Title: The flight crew of a King Air was unable to disconnect the autopilot when it failed to level at their cleared altitude. Control was regained 1;000 FT below their cleared altitude after they pulled the autopilot circuit breaker.

Narrative: As we approached our destination we were given an initial descent and then a continuing descent to 4;000 FT. I was looking at the approach plate for the expected approach when I looked at the altitude and noticed that the rate of descent was not slowing to capture our cleared altitude. I said something to the pilot flying and he pressed the disconnect for the autopilot. At the time we thought the autopilot disconnected. As he tried to pull back on the controls; I noticed the trim start to move. I thought we had a problem with the trim. At this time we descended through our assigned altitude. I advised ATC we had a problem and to standby. We continued to descend slightly below 3;000 FT with both of us trying to override the trim. I then noticed the autopilot had not disconnected. We both tried to disconnect without success and the other pilot tried the pedestal disconnect without success. I then pulled the circuit breaker for the autopilot and at that time we regained control of the aircraft and advised ATC we had the situation under control and could continue.

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.

The flight crew of a king air was unable to disconnect the autopilot when it failed to level at their cleared altitude. Control was regained 1;000 ft below their cleared altitude after they pulled the autopilot circuit breaker.