Narrative:

Captain was pilot flying. First officer was pilot monitoring. Aircraft was at 5;000 ft. When ATC cleared flight to proceed direct the FAF (final approach fix); to cross the FAF at or above 2;000 ft. And cleared flight for the ILS approach. When level at 2;000 ft.; the aircraft was approximately 30 to 35 miles south of the FAF on an intercept course greater than 90 degrees. The aircraft's heading had previously been established when ATC cleared flight to proceed direct. While proceeding direct the pilot monitoring made call 'flight instruments verified' the pilot flying also verified ILS via morse code identifier. Pilot flying did not select approach mode as flight was still almost on a 90 degree intercept to final and still in heading mode. Pilot flying began to turn the heading bug with the intent to position he aircraft on an intercept less than 90 degrees so that approach mode could be selected. While level at 2;000 ft.; approximately 30 to 35 miles south of the FAF both captain and first officer displayed localizer and GS and the flight director/auto pilot captured this localizer and GS. The aircraft then made an immediate 30 degree bank and began a descent exceeding 1;500 ft. Per minute. The crew queried each other about the localizer and GS capturing at the exact same time. The pilot flying then realized the flight path was not in line with the mfd. As the pilot flying was about to ask the pilot monitoring to contact ATC for heading; ATC contacted flight. The pilot flying disconnected the autopilot and asked the pilot monitoring to tell ATC we need a vector back to the FAF. At that moment ATC contacted the flight and asked are we still direct. The pilot monitoring replied and then a second controller asked why we were below 2;000 ft. The pilot monitoring told ATC the aircraft autopilot indicated it captured localizer/GS. The flight director/autopilot responded to something; but it was not the localizer and GS for the ILS at our destination. This resulted in lateral and vertical deviations from the ATC clearance. ATC gave instruction to climb to 2;000 ft. And a heading back to the FAF. The flight was then given vectors back to the FAF on a significantly less intercept course with normal approach and landing. At no time was the aircraft on any known ILS associated with our destination. After landing; captain contacted TRACON and spoke with a TRACON controller who stated there's no issues with the ILS that he was aware of. No other localizers are in the vicinity. The controller also stated he had been working that sector and there had been no anomalies. This flight had a captain in the jump seat during the entire event. The jump seater witnessed the aircraft 'behave' as though it had captured a localizer and GS. Upon landing the crew reviewed the maintenance log which indicated the aircraft had at least two recent entries regarding flight director and autopilot malfunction. These previous entries indicated flight director anomalies during approach mode and not in-flight. This is consistent with what we experienced. The flight director functioned normally during all other phases of flight. Flight director and autopilot maintenance log entries should appear on the release with date and time of event.

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Original NASA ASRS Text

Title: ERJ145 Flight Crew reported that an autopilot malfunction on approach resulted in a course and altitude deviation.

Narrative: Captain was Pilot Flying. First Officer was Pilot Monitoring. Aircraft was at 5;000 ft. when ATC cleared flight to proceed direct the FAF (Final Approach Fix); to cross the FAF at or above 2;000 ft. and cleared flight for the ILS Approach. When level at 2;000 ft.; the aircraft was approximately 30 to 35 miles south of the FAF on an intercept course greater than 90 degrees. The aircraft's heading had previously been established when ATC cleared flight to proceed direct. While proceeding direct the Pilot Monitoring made call 'flight instruments verified' The Pilot Flying also verified ILS via Morse code identifier. Pilot Flying did not select Approach Mode as flight was still almost on a 90 degree intercept to final and still in heading mode. Pilot Flying began to turn the heading bug with the intent to position he aircraft on an intercept less than 90 degrees so that Approach Mode could be selected. While level at 2;000 ft.; approximately 30 to 35 miles south of the FAF both Captain and First Officer displayed LOC and GS and the flight director/auto pilot captured this LOC and GS. The Aircraft then made an immediate 30 degree bank and began a descent exceeding 1;500 ft. per minute. The crew queried each other about the LOC and GS capturing at the exact same time. The Pilot Flying then realized the flight path was not in line with the MFD. As the Pilot Flying was about to ask the Pilot Monitoring to contact ATC for heading; ATC contacted flight. The Pilot Flying disconnected the autopilot and asked the Pilot Monitoring to tell ATC we need a vector back to the FAF. At that moment ATC contacted the flight and asked are we still direct. The Pilot Monitoring replied and then a second controller asked why we were below 2;000 ft. The Pilot Monitoring told ATC the aircraft autopilot indicated it captured LOC/GS. The flight director/autopilot responded to something; but it was not the LOC and GS for the ILS at our destination. This resulted in lateral and vertical deviations from the ATC clearance. ATC gave instruction to climb to 2;000 ft. and a heading back to the FAF. The flight was then given vectors back to the FAF on a significantly less intercept course with normal approach and landing. At no time was the aircraft on any known ILS associated with our destination. After landing; Captain contacted TRACON and spoke with a TRACON Controller who stated there's no issues with the ILS that he was aware of. No other localizers are in the vicinity. The Controller also stated he had been working that sector and there had been no anomalies. This flight had a Captain in the jump seat during the entire event. The jump seater witnessed the aircraft 'behave' as though it had captured a LOC and GS. Upon landing the crew reviewed the maintenance log which indicated the aircraft had at least two recent entries regarding flight director and autopilot malfunction. These previous entries indicated flight director anomalies during approach mode and not in-flight. This is consistent with what we experienced. The flight director functioned normally during all other phases of flight. Flight director and autopilot Maintenance Log entries should appear on the release with date and time of event.

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.