Date: 201901
Local time of day: 1201-1800
Location: D10.TRACON, TX
Flight conditions: VMC
Light: Night
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B D10
ATC / advisory: TRACON D10
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC Overrode Automation; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

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.


Second narrative: While level at 11;000 MSL on the BOOVE4 STAR into DFW and within 1 nm of the DELMO intersection; (auto-pilot engaged) the aircraft began turning at DELMO approaching the end of the STAR. We received two caution messages AP TRIM IS NU and AP TRIM is LWD simultaneously. Seconds after receiving the messages we observed the aircraft pitch nose down and began a slight descent reaching 10;800 MSL although there was no input or change put into the flight director or command given to the aircraft. As PF; I immediately disengaged the auto-pilot and attempted to return to the 11;000 MSL altitude for the crossing at DELMO. As this occurred; ATC instructed to descend to 6;000 MSL and the aircraft began to turn via the STAR. Once the AP was disconnected the trim forces on the aircraft were strong and caused the aircraft to further pitch down which required an initial amount of physical strength to retard the initial descents. The aircraft reached 10;600 MSL. While hand flying and correcting the un-commanded action of the aircraft; ATC asked if/why we began our descent early. The PM responded that we were experiencing an auto pilot issue. The aircraft was hand flown and the correct flight path was establish at a speed of 220 knots and descending to 6;000 MSL. Once certain the aircrafts flight path was established; the PF requested AP engaged and the remainder of the STAR and beginning of the approach was flown via the flight director and autopilot and observed to be normal. The AP was disengaged on the approach and landing were made in VMC conditions and hand flown. Failure of autopilot; automation; and mechanical failure of autopilot unable to fly the commanded inputs of the flight director due to a caution message AP TRIM IS NU and AP TRIM IS LWD. Resolving recurring maintenance issues concerning automation or MEL for automations issues.


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