While in a descent an md-80 flight crew overshot the level-off at 12;000 feet because the altitude c...

Attributes
ACN	1228052
Time
Date	201412
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Altitude Hold/Capture
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Overshoot Deviation - Procedural Clearance

Narrative:

Descending via the RNAV arrival; we were cleared to cross ZZZ intersection at 12;000 feet MSL and 250 knots. Approaching 12;000 feet; altitude cap annunciated properly; then altitude hld annunciated properly. The nose then dropped and the aircraft continued to descend. Captain re-selected altitude hld mode with no effect. Captain then rolled the vertical speed into a positive rate of climb with no effect. He then disconnected the autopilot and hand flew the aircraft smoothly back to the proper altitude of 12;000 feet. Lowest altitude reached during the event was approximately 11;550 feet (450 feet below assigned altitude).at 12;000 feet MSL; the autopilot was re-engaged for a test. The nose of the aircraft once again lowered into a descent while altitude hld mode remained annunciated. The ap trm also annunciated at this time. Autopilot was disconnected and the aircraft was hand flown on the remainder of the arrival and approach. Maintenance was notified and briefed on the failure upon gate arrival. Follow on crew was also briefed on the event and failure.

Original NASA ASRS Text

Title: While in a descent an MD-80 flight crew overshot the level-off at 12;000 feet because the altitude capture feature failed. They disconnected the autopilot and hand flew the aircraft to a successful landing.

Narrative: Descending via the RNAV Arrival; we were cleared to cross ZZZ intersection at 12;000 feet MSL and 250 knots. Approaching 12;000 feet; ALT CAP annunciated properly; then ALT HLD annunciated properly. The nose then dropped and the aircraft continued to descend. Captain re-selected ALT HLD mode with no effect. Captain then rolled the Vertical Speed into a positive rate of climb with no effect. He then disconnected the Autopilot and hand flew the aircraft smoothly back to the proper altitude of 12;000 feet. Lowest altitude reached during the event was approximately 11;550 feet (450 feet below assigned altitude).At 12;000 feet MSL; the autopilot was re-engaged for a test. The nose of the aircraft once again lowered into a descent while ALT HLD mode remained annunciated. The AP TRM also annunciated at this time. Autopilot was disconnected and the aircraft was hand flown on the remainder of the arrival and approach. Maintenance was notified and briefed on the failure upon gate arrival. Follow on crew was also briefed on the event and failure.

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.

While in a descent an md-80 flight crew overshot the level-off at 12;000 feet because the altitude capture feature failed. They disconnected the autopilot and hand flew the aircraft to a successful landing.