Narrative:

We were flying into teterboro at the end of a long day with over 8 hours of block time at the end of this flight. We had been vectored onto the approach for the ILS 6 circle to runway 1 at 2;000 ft with the autopilot on. The clearance read 'maintain 2;000 ft until established; cleared for the ILS 6 circle runway 1; cross dandy at 1;500 ft; maintain 180 KTS until dandy.' I read back the clearance; and selected 1;500 in the altitude selector. Once cleared for the approach the 'approach' mode was selected on the autopilot. Shortly after this; the aircraft began an uncommanded climb; I announced 'climbing; climbing' to the pilot flying. As the aircraft approached 2;200 ft; the pilot flying was taken off guard so I took the controls and disconnected the autopilot. By the time I got power reduced and the aircraft pitched over; we had nearly reached 2;400 ft. I quickly descended the airplane back to 2;000 ft and continued the descent to cross dandy at 1;500. Before I returned to 2;000 ft; ATC said 'your clearance is to cross dandy at 1;500 I show you climbing'. I responded; 'affirmative; descending to 1;500' as I executed the descent. We continued the hand flown approach to landing without further incident.I am not sure what caused the uncommanded climb. There is no reason the autopilot should have begun a climb under the circumstances unless another mode was incorrectly set; but with the altitude selected to 1;500; it should not have climbed at all. Even after I tried to reselect the approach mode the command bars showed climb so I continued the approach in VMC using raw data.

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Original NASA ASRS Text

Title: BE400 Captain is cleared for the ILS 6 circle to Runway 1 at TEB and cross DANDY at 1;500 FT. With the autopilot engaged at 2;000 FT the aircraft suddenly begins a climb which is not arrested before 2;400 FT. A hand flown approach and landing is then completed.

Narrative: We were flying into Teterboro at the end of a long day with over 8 hours of block time at the end of this flight. We had been vectored onto the approach for the ILS 6 circle to Runway 1 at 2;000 FT with the autopilot on. The clearance read 'maintain 2;000 FT until established; cleared for the ILS 6 circle Runway 1; cross DANDY at 1;500 FT; maintain 180 KTS until DANDY.' I read back the clearance; and selected 1;500 in the altitude selector. Once cleared for the approach the 'Approach' mode was selected on the autopilot. Shortly after this; the aircraft began an uncommanded climb; I announced 'climbing; climbing' to the pilot flying. As the aircraft approached 2;200 FT; The pilot flying was taken off guard so I took the controls and disconnected the autopilot. By the time I got power reduced and the aircraft pitched over; we had nearly reached 2;400 FT. I quickly descended the airplane back to 2;000 FT and continued the descent to cross DANDY at 1;500. Before I returned to 2;000 FT; ATC said 'your clearance is to cross DANDY at 1;500 I show you climbing'. I responded; 'Affirmative; descending to 1;500' as I executed the descent. We continued the hand flown approach to landing without further incident.I am not sure what caused the uncommanded climb. There is no reason the autopilot should have begun a climb under the circumstances unless another mode was incorrectly set; but with the altitude selected to 1;500; it should not have climbed at all. Even after I tried to reselect the approach mode the command bars showed climb so I continued the approach in VMC using raw data.

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.