A falcon 2000 captain reported an uncommanded climb from 2;000 feet to capture the ILS glideslope fr...

Narrative:

We were flying the ILS 19 approach. We had been level for a few minutes at 2;000 MSL with the autopilot on and cleared for the ILS. The ILS approach was armed and the plane captured the course normally. We were configured with 10 degrees of flaps and told to slow to 150 KIAS. While slowing and preparing to finish configuring; the aircraft began a climb while on the autopilot. It departed 2;000 MSL and appeared to be climbing up to capture the glideslope. This is abnormal behavior and the autopilot should have maintained 2;000 MSL while the glideslope descended for capture. The monitoring pilot called out that the plane was climbing. The autopilot was clicked off by the flying pilot and a descent back to 2;000 MSL initiated. After the flight; the monitoring pilot stated the climb onset rapidly and rate was about 1;000 feet per minute. The altitude was at least 300 feet high above the cleared 2;000 MSL before the autopilot was clicked off and the aircraft flown manually back to 2;000 MSL. Then we did a normal capture of the ILS glideslope manually. The controller did not comment about the altitude and we continued the approach safely to a landing. We said nothing to the controller either as the airspace was extremely congested.

Original NASA ASRS Text

Title: A Falcon 2000 Captain reported an uncommanded climb from 2;000 feet to capture the ILS glideslope from below; so the autopilot was disconnected and returned to the cleared altitude then continued the ILS approach manually.

Narrative: We were flying the ILS 19 approach. We had been level for a few minutes at 2;000 MSL with the autopilot on and cleared for the ILS. The ILS approach was armed and the plane captured the course normally. We were configured with 10 degrees of flaps and told to slow to 150 KIAS. While slowing and preparing to finish configuring; the aircraft began a climb while on the autopilot. It departed 2;000 MSL and appeared to be climbing up to capture the glideslope. This is abnormal behavior and the autopilot should have maintained 2;000 MSL while the glideslope descended for capture. The monitoring pilot called out that the plane was climbing. The autopilot was clicked off by the flying pilot and a descent back to 2;000 MSL initiated. After the flight; the monitoring pilot stated the climb onset rapidly and rate was about 1;000 feet per minute. The altitude was at least 300 feet high above the cleared 2;000 MSL before the autopilot was clicked off and the aircraft flown manually back to 2;000 MSL. Then we did a normal capture of the ILS glideslope manually. The controller did not comment about the altitude and we continued the approach safely to a landing. We said nothing to the controller either as the airspace was extremely congested.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1310998
Time
Date	201511
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	Falcon 2000
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	Approach Coupler
Person 1
Function	Captain
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 35 Flight Crew Total 6670 Flight Crew Type 247
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance

A falcon 2000 captain reported an uncommanded climb from 2;000 feet to capture the ILS glideslope from below; so the autopilot was disconnected and returned to the cleared altitude then continued the ILS approach manually.