B767 flight crew reported on final approach (localizer capture) the autothrottle system experienced ...

Attributes
ACN	1618944
Time
Date	201902
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZZ.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Autothrottle/Speed Control
Person 1
Function	Relief Pilot First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Commercial Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 175 Flight Crew Type 2137
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Commercial Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 207 Flight Crew Type 4064
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Speed All Types Inflight Event / Encounter Unstabilized Approach

Narrative:

[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 localizer/ILS; descending to 2;000 feet in flight level change 'flch'; flaps 20 speed 190 knots. At localizer 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.

Original NASA ASRS Text

Title: B767 flight crew reported on final approach (LOC capture) the autothrottle system experienced a malfunction which resulted in an uncommand climb and acceleration.

Narrative: [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.

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.

B767 flight crew reported on final approach (localizer capture) the autothrottle system experienced a malfunction which resulted in an uncommand climb and acceleration.