B787 Captain reported an Auto Throttle failure and the associated Indication and Warning Systems allowed the aircraft's airspeed to become dangerously low. The flight crew took immediate action upon recognizing the threat and was able to continue the approach to landing at the destination airport.

Narrative

Auto Throttle failed to capture target speed; no AUTO ACTIVATION; no AIRSPEED LOW. ZZZZ; ZZZZZ Arrival; to ILS Runway XX. Hard altitude 2;500 ft. placed at ZZZZZ1 and FAF; APP armed. Used FLCH SPD transitioning to ALT at 2;500 ft. / ZZZZZ1. Leveling at 2;500 ft. outside the FAF; Aircraft was being slowed to TGT speed; flaps changing 25 to 30. With the Autopilot successfully leveling off the Auto Throttle remained at Idle and allowed the Aircraft to slow below MIN MANEUVERING SPEED. The confluence of above events seemed to overwhelm the auto-throttle computer: NOTE: NO AIRSPEED LOW was annunciated from the aircraft while the speed went below min maneuvering speed. NOTE: NO auto-throttle AUTOMATIC Aircraft/ wake-up happened to maintain MIN MANEUVERING SPEED. Captain monitoring pushed throttles that were at idle; as did the First Officer; to arrest the deceleration below min maneuvering speed. Deceleration was successfully stopped above stick shaker. With under wing engines the Aircraft pitched up slightly; the approximately 60 foot climb in landing configuration slowing recovery. By the FAF / descent segment all was back to normal; stabilized and a normal landing proceeded. Entered a Maintenance report and verbally described the problem to a Maintenance Technician.