Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 188
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Executed Go Around / Missed Approach; Flight Crew Diverted; General Maintenance Action
Aircraft
While intercepting the localizer course for ILS Runway 10 BWI Approach from the north and just outside of the final approach fix; VOR/LOC captured and then the aircraft made an abrupt continuous right turn away from the inbound course. The localizer was rapidly moving through half scale deflection to the left and the First Officer disengaged the autopilot to begin a go-around. At that time; assuming because of the aircraft position; the Approach Controller asked if we would like to be vectored back around for another ILS. We said we would and proceeded to come around for another approach. On our second attempt at the ILS 10 BWI Approach; upon VOR/LOC capture the same automation error occurred with the same abrupt right turn. The PF went around; and during the maneuver the aircraft crossed over the final approach course to the north and we were given radar vectors by ATC for the remainder of the missed approach. The crew then made the decision to proceed to our alternate; which was VFR; due to the weather conditions in BWI and the unexpected behavior of the aircraft.
[Report narrative contained no additional information.]
B737 flight crew reported diverting to a VFR alternate after their autoflight system malfunctioned twice on the BWI Runway 10 ILS.