Narrative:

While on the onyon one arrival we were cleared the arrival routing for the ILS precision runway monitor (prm) runway (runway) 8L. Prior to the downwind leg; the approach controller provided the current RVR of >6000. When on the radar downwind the weather was updated to 2600 RVR. I was flying and the captain briefed the changes in procedure required for a monitored approach. About the time the controller turned us to a 180 heading for the base leg the master caution flashed and the EICAS message 'ap trim is lwd' flashed for about a second and both lights extinguished. The autopilot continued to function fine. We were given a 120 heading and cleared for the ILS prm runway 8L. While on the ILS final; the aircraft 2 ahead on the approach landed and provided a PIREP that they had the runway lights in sight at 450 feet AGL. Our approach was uneventful and stable until 500 feet AGL. At approximately 500 feet AGL; the pilot not flying (PNF) glanced outside searching for the approach/runway lighting. I noted the command bars direct a right turn and an amber boxed 'a' flash on the pfd for about 1 second. I cross checked that the aircraft was on course and on glide path as the aircraft entered a right bank turn. I was initiating a go-around simultaneously as the PNF looked back inside and directed a go-around. The aircraft had reached approximately 10 degrees right bank as I pushed the take off go around (toga) button; pushed the power up; leveled the wings and raised the nose to 7-10 degrees nose up. I simultaneously directed 'set go-around power; spoilers in and flaps 8.' the PNF set the power; reset the flaps to 8 and notified the tower of our missed approach. Tower then stated; 'you are headed toward runway 8R.' I then began the missed approach turn to the north noting the altimeter read 1700 feet. Tower handed us off to atlanta approach. We were given a heading of 270 and altitude of 5000 feet to put us back in sequence for the ILS prm runway 8L. The controller provided updated weather of touchdown RVR 1800; mid-point RVR 1600 and roll-out RVR 1800. We flew an uneventful monitored ILS with the captain going 'visual' at 200 feet AGL.changing weather due to the fog setting in right at sunset provided the greatest environmental threat. We had briefed and were prepared for monitored approach procedures to aid in mitigating this threat. The autopilot/flight director error during a high workload phase of flight compounded the low visibility threat. The aircraft autopilot/flight director error caused the aircraft to turn off course and result in a course deviation and an undesired aircraft state on short final in the weather. The undesired state was realized and an immediate missed approach/go-around was executed.go-arounds are in frequent and missed approaches are even more infrequent. This is the first actual missed approach in the aircraft I had flown. Out of about 210 flights I had only gone around once. The training department is very adamant about planning approaches to go missed. That way you are best prepared for the missed approach procedure. The challenge is maintaining that mindset. Even tougher when aircraft in front of you are providing PIREP's and landing from the approach. I was vigilant during the approach but I do admit the autopilot directing a turn away from course was surprising. Although it probably took a second to recognize and react; the undesired aircraft state (course deviation) happened quickly. The tower advisory interrupted the flow of the go-around procedure and we did not retract the gear until initiating the turn to the north. Also; in accordance with the published missed approach; I should have turned toward the north at 1500 feet. A lot happens quickly during a missed approach and I now know it probably won't go as cleanly as in training. If external factors are causing the missed to not go cleanly; I will just stay on the profile. Even more so now; I fully appreciate the mindset of planning every approach to a missed approach. One item the training shop may want to introduce is a missed approach due to a minor aircraft/navigation/flight director system malfunction. As I recall most every missed approach in training was due to weather below minimums.

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Original NASA ASRS Text

Title: A CRJ200 Flight Crew experiences an autopilot malfunction at 500 feet AGL during a low visibility approach to Runway 8L at ATL. A missed approach is initiated but not before the aircraft has turned 15 degrees toward 8R. When the Take Off Go Around (TOGA) button is pushed the autopilot disconnects causing a late turn away from Runway 8R and late gear retraction. The second approach is a Category (CAT) III and successful.

Narrative: While on the ONYON One Arrival we were cleared the arrival routing for the ILS Precision Runway Monitor (PRM) Runway (RWY) 8L. Prior to the downwind leg; the approach controller provided the current RVR of >6000. When on the radar downwind the weather was updated to 2600 RVR. I was flying and the Captain briefed the changes in procedure required for a Monitored Approach. About the time the controller turned us to a 180 heading for the base leg the master caution flashed and the EICAS message 'AP TRIM IS LWD' flashed for about a second and both lights extinguished. The autopilot continued to function fine. We were given a 120 heading and cleared for the ILS PRM RWY 8L. While on the ILS final; the aircraft 2 ahead on the approach landed and provided a PIREP that they had the runway lights in sight at 450 feet AGL. Our approach was uneventful and stable until 500 feet AGL. At approximately 500 feet AGL; the Pilot Not Flying (PNF) glanced outside searching for the approach/runway lighting. I noted the command bars direct a right turn and an amber boxed 'A' flash on the PFD for about 1 second. I cross checked that the aircraft was on course and on glide path as the aircraft entered a right bank turn. I was initiating a go-around simultaneously as the PNF looked back inside and directed a go-around. The aircraft had reached approximately 10 degrees right bank as I pushed the Take Off Go Around (TOGA) button; pushed the power up; leveled the wings and raised the nose to 7-10 degrees nose up. I simultaneously directed 'set go-around power; spoilers in and flaps 8.' The PNF set the power; reset the flaps to 8 and notified the tower of our missed approach. Tower then stated; 'you are headed toward runway 8R.' I then began the missed approach turn to the north noting the altimeter read 1700 feet. Tower handed us off to Atlanta Approach. We were given a heading of 270 and altitude of 5000 feet to put us back in sequence for the ILS PRM RWY 8L. The controller provided updated weather of touchdown RVR 1800; mid-point RVR 1600 and roll-out RVR 1800. We flew an uneventful monitored ILS with the Captain going 'visual' at 200 feet AGL.Changing weather due to the fog setting in right at sunset provided the greatest environmental threat. We had briefed and were prepared for monitored approach procedures to aid in mitigating this threat. The autopilot/flight director error during a high workload phase of flight compounded the low visibility threat. The aircraft autopilot/flight director error caused the aircraft to turn off course and result in a course deviation and an undesired aircraft state on short final in the weather. The undesired state was realized and an immediate missed approach/go-around was executed.Go-arounds are in frequent and missed approaches are even more infrequent. This is the first actual missed approach in the aircraft I had flown. Out of about 210 flights I had only gone around once. The training department is very adamant about planning approaches to go missed. That way you are best prepared for the missed approach procedure. The challenge is maintaining that mindset. Even tougher when aircraft in front of you are providing PIREP's and landing from the approach. I was vigilant during the approach but I do admit the autopilot directing a turn away from course was surprising. Although it probably took a second to recognize and react; the undesired aircraft state (course deviation) happened quickly. The tower advisory interrupted the flow of the go-around procedure and we did not retract the gear until initiating the turn to the north. Also; in accordance with the published missed approach; I should have turned toward the north at 1500 feet. A lot happens quickly during a missed approach and I now know it probably won't go as cleanly as in training. If external factors are causing the missed to not go cleanly; I will just stay on the profile. Even more so now; I fully appreciate the mindset of planning every approach to a missed approach. One item the training shop may want to introduce is a missed approach due to a minor aircraft/navigation/flight director system malfunction. As I recall most every missed approach in training was due to weather below minimums.

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.