Crj-700 flight crew reported an autopilot issue resulted in an altitude deviation while on the boove...

Attributes
ACN	1609307
Time
Date	201901
Local Time Of Day	1201-1800
Place
Locale Reference	D10.TRACON
State Reference	TX
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Regional Jet 700 ER/LR (CRJ700)
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

The event occurred while we were flying the boove 4 STAR into dfw. I was pm (pilot monitoring) during the event. While the aircraft was level at 11;000 MSL (with the auto-pilot engaged) turning the corner at delmo approaching the end of the STAR with previously crossing traffic at 10;000 MSL we received an ap trim is nu and an ap trim is lwd simultaneously. Approximately one to two seconds after the message occurred we saw that the aircraft was no longer following the flight director and in a descent. The PF (pilot flying) immediately dis-engaged the auto-pilot and attempted to return to 11;000 MSL. When auto-pilot was disconnected at 10;800 MSL it abruptly pitched down further with a total altitude loss of 400 feet; bringing the altitude down to 10;600 MSL the PF further corrected and returned to 11;000 MSL. While we were correcting dfw regional approach control contacted us and cleared us down to 6;000 MSL and asked us why we had started descending. To which we replied that we had just had an auto-pilot issue. The cause of this event was a failure of automation and a mechanical failure of the auto-pilot. More attention to recurring maintenance issues to solve them indefinitely.

Original NASA ASRS Text

Title: CRJ-700 flight crew reported an autopilot issue resulted in an altitude deviation while on the BOOVE 4 STAR to DFW airport.

Narrative: The event occurred while we were flying the BOOVE 4 STAR into DFW. I was PM (Pilot Monitoring) during the event. While the aircraft was level at 11;000 MSL (with the auto-pilot engaged) turning the corner at DELMO approaching the end of the STAR with previously crossing traffic at 10;000 MSL we received an AP TRIM IS NU and an AP TRIM IS LWD simultaneously. Approximately one to two seconds after the message occurred we saw that the aircraft was no longer following the flight director and in a descent. The PF (Pilot Flying) immediately dis-engaged the auto-pilot and attempted to return to 11;000 MSL. When auto-pilot was disconnected at 10;800 MSL it abruptly pitched down further with a total altitude loss of 400 feet; bringing the altitude down to 10;600 MSL the PF further corrected and returned to 11;000 MSL. While we were correcting DFW regional approach control contacted us and cleared us down to 6;000 MSL and asked us why we had started descending. To which we replied that we had just had an auto-pilot issue. The cause of this event was a failure of automation and a mechanical failure of the auto-pilot. More attention to recurring maintenance issues to solve them indefinitely.

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.

Crj-700 flight crew reported an autopilot issue resulted in an altitude deviation while on the boove 4 STAR to dfw airport.