Narrative:

On climb out passing through approximately 7;000 ft; we received an 'EFIS comp mon' caution message immediately followed by an ap trim is nd (autopilot trim is nose down) caution message. I instinctively looked at the elevator trim display and observed the trim running nose down. I immediately pushed the stab trim disconnect and instructed the first officer to do the same. I assumed control of the aircraft and told the first officer to request a level off at 10;000 ft from ATC. As he was doing that I disconnected the autopilot and found it to be excessively out of trim to the point that it was very difficult to control. I instructed him to run the stab trim runaway checklist. Although we never heard the trim clacker; it seemed at the time the more prudent checklist to run.I had the first officer request a turn back towards [departure airport] as a precaution although we had not committed yet to a return. During this turn I lost some altitude due to the excessive nose down trim as the primary cause but was able to gain it back. Upon further reflection; I decided to run the ap trim is nd checklist because I felt that the autopilot was the more probable cause. I reengaged the trim and trimmed the aircraft for level flight. We did not experience any trim runaway.after briefing the first officer about the autopilot possibly driving the trim nose down; a reengaged the autopilot per the checklist. Immediately the trim started moving nose down so I once again disconnected the trim and the autopilot. I reengaged the trim and left the autopilot off. I determined the autopilot had malfunctioned and since at this time we had full control of the aircraft; I elected to not [get priority handling]. I had the first officer request a return to [departure airport] and instructed him to notify the flight attendants and to ACARS dispatch. We returned and landed uneventfully.

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Original NASA ASRS Text

Title: CRJ-700 Captain reported returning to departure airport after experiencing an autopilot malfunction that drove the stabilizer trim to a nose-down position.

Narrative: On climb out passing through approximately 7;000 FT; we received an 'EFIS COMP MON' caution message immediately followed by an AP TRIM IS ND (Autopilot Trim is Nose Down) caution message. I instinctively looked at the elevator trim display and observed the trim running nose down. I immediately pushed the stab trim disconnect and instructed the First Officer to do the same. I assumed control of the aircraft and told the First Officer to request a level off at 10;000 FT from ATC. As he was doing that I disconnected the Autopilot and found it to be excessively out of trim to the point that it was very difficult to control. I instructed him to run the Stab Trim Runaway checklist. Although we never heard the trim clacker; it seemed at the time the more prudent checklist to run.I had the First Officer request a turn back towards [departure airport] as a precaution although we had not committed yet to a return. During this turn I lost some altitude due to the excessive nose down trim as the primary cause but was able to gain it back. Upon further reflection; I decided to run the AP TRIM IS ND checklist because I felt that the Autopilot was the more probable cause. I reengaged the trim and trimmed the aircraft for level flight. We did not experience any trim runaway.After briefing the First Officer about the Autopilot possibly driving the trim nose down; a reengaged the Autopilot per the checklist. Immediately the trim started moving nose down so I once again disconnected the trim and the Autopilot. I reengaged the trim and left the Autopilot off. I determined the Autopilot had malfunctioned and since at this time we had full control of the aircraft; I elected to not [get priority handling]. I had the First Officer request a return to [departure airport] and instructed him to notify the flight attendants and to ACARS dispatch. We returned and landed uneventfully.

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.