Global 6000 flight crew reported an altitude overshoot during approach due to an autopilot malfuncti...

Attributes
ACN	1518886
Time
Date	201802
Local Time Of Day	1201-1800
Place
Locale Reference	BMI.Airport
State Reference	IL
Environment
Light	Daylight
Aircraft 1
Make Model Name	Global 6000 (Bombardier)
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	None
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 10 Flight Crew Total 11300 Flight Crew Type 750
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 47 Flight Crew Total 11550 Flight Crew Type 800
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Overshoot Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

ATC cleared our aircraft from 6000 ft to 2500 ft; and once established; cleared us for the ILS 20 approach at bmi. I was PF (pilot flying) using auto-pilot in heading and vertical speed for a descent and vector to intercept. Correct altitude was set in altitude pre-selector. At 2;500 ft 'alt cap' annunciated; however [the] aircraft continued descent; climb was initiated manually almost immediately back to 2;500 ft. Estimate altitude loss of 250 ft. Below cleared altitude. Pia approach alerted us to low altitude warning while we were in the climb to 2;500 ft; continued approach to normal landing.check and verify automation is doing what it is supposed to be doing.

Original NASA ASRS Text

Title: Global 6000 flight crew reported an altitude overshoot during approach due to an autopilot malfunction.

Narrative: ATC cleared our aircraft from 6000 ft to 2500 ft; and once established; cleared us for the ILS 20 approach at BMI. I was PF (Pilot Flying) using auto-pilot in Heading and Vertical Speed for a descent and vector to intercept. Correct altitude was set in altitude pre-selector. At 2;500 ft 'Alt Cap' annunciated; however [the] aircraft continued descent; Climb was initiated manually almost immediately back to 2;500 ft. Estimate altitude loss of 250 ft. below cleared altitude. PIA approach alerted us to low altitude warning while we were in the climb to 2;500 ft; continued approach to normal landing.Check and verify automation is doing what it is supposed to be doing.

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.