A ce-560XLS level and stabilized at 3;000 ft pitched up when approach flaps were selected.

Attributes
ACN	841073
Time
Date	200906
Local Time Of Day	1801-2400
Place
Locale Reference	TEB.Airport
State Reference	NJ
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Citation Excel (C560XL)
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Altitude Hold/Capture
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Flight Instructor Flight Crew Flight Engineer
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 10000 Flight Crew Type 50
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude

Narrative:

While level at 4000 ft approximately 16 miles out established on the localizer for the ILS 19 teb; we were cleared to 3000 ft. The aircraft was established and level at 3000' with the autopilot selected on. The localizer had been captured and approach had been selected as we had been cleared for the approach. At approximately 2-3 miles prior to unvil the autopilot initiated an un-commanded pitch up and climb when approach flaps were selected. The aircraft pitched slightly in reaction to the movement of the flaps but instead of adjusting and maintaining altitude; the autopilot initiated an un-commanded climb; at which time I disengaged the autopilot and recovered to the assigned altitude. We continued the approach and landed without further incident.

Original NASA ASRS Text

Title: A CE-560XLS level and stabilized at 3;000 FT pitched up when approach flaps were selected.

Narrative: While level at 4000 FT approximately 16 miles out established on the localizer for the ILS 19 TEB; we were cleared to 3000 FT. The aircraft was established and level at 3000' with the autopilot selected on. The localizer had been captured and approach had been selected as we had been cleared for the approach. At approximately 2-3 miles prior to UNVIL the autopilot initiated an un-commanded pitch up and climb when approach flaps were selected. The aircraft pitched slightly in reaction to the movement of the flaps but instead of adjusting and maintaining altitude; the autopilot initiated an un-commanded climb; at which time I disengaged the autopilot and recovered to the assigned altitude. We continued the approach and landed 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.