B767 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 175; Flight Crew Type 2137
Workload; Time Pressure; Distraction; Confusion
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Unstabilized Approach
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action; Flight Crew Regained Aircraft Control; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; Flight Crew Executed Go Around / Missed Approach
Aircraft
[I was] relief pilot at time of occurrence. Left autopilot and autothrottles engaged. The flight was in an auto-flight descent and on ATC vectors heading 155 to intercept Runway XXR LOC/ILS; descending to 2;000 feet in Flight Level Change 'FLCH'; flaps 20 speed 190 knots. At LOC capture and in the turn descending through 2;100 feet the aircraft began an uncommanded climb and acceleration. At 210 knots the autopilot was disconnected and hand flown back to 2;000 with autothrottles engaged. Crew observed the airspeed now decreasing below 190 knots which alerted crew of potential autothrottle malfunction. Autothrottle was disconnected for remainder of the approach and landing. At no time did the crew observe a deviation off of the localizer course. Due to the unexplained altitude climb ATC broke the flight off the approach and vectored us around for an uneventful Runway XXR ILS approach and landing. Once the aircraft was stabilized at 2;000 feet left autopilot was reengaged until approximately 1200 feet AGL when autopilot was disconnected and a normal landing was accomplished. After we blocked in the auto-flight system malfunction was logged as a maintenance discrepancy.
[Report narrative contained no additional information.]
B767 flight crew reported on final approach (LOC capture) the autothrottle system experienced a malfunction which resulted in an uncommand climb and acceleration.