Narrative:

On flight XXXX; ZZZ-ZZZ1; date; the crew experienced 2 high speed events during the descent into ZZZ1. While descending from cruise altitude it became necessary to expedite descent and slow the aircraft. As the PF; I retarded the throttles and extended the airbrake; configuring the aircraft for a 250 kt. Descent. Upon doing so; the aircraft responded with an unexpected and unusual nose low attitude of approximately 15 degrees which caused rapid acceleration. The immediate reaction at that time was to retract the brake in order to clean the configuration of the aircraft and interrupt the pitch with tcs (touch control steering) and pull carefully back into a less accelerative attitude. While the aircraft was being slowed; the highspeed warning annunciated and was active for approximately 8 seconds. The pm monitored the pitch and speed; and through proper coordination and manual control the aircraft was brought into a normal profile by disabling the previously selected speed descent. After stabilizing the descent; the crew discussed the proximity to the airport and the relatively high altitude of the aircraft in order to proactively warn ATC of assistance. South turns were requested and executed. During coordination with ATC and at approximately 12;000 ft I; the PF selected a flight crew descent with speed brake to attempt to bring the aircraft through 10;000 with proper speed. The aircraft responded again with unusually steep downward pitch; and expecting this; faster action to apply tcs and reconfigure the aircraft for a hand flown descent was enacted by both crewmembers. Even with swift corrective action; the aircraft did accelerate to approximately 280 kts for a period of roughly 5 seconds. The approach and landing phases of flight were then safely executed without ap. After landing a normal shutdown was performed; aml entry was made; and the pm contacted maintenance control and described the event in detail. Afterward; the crew debriefed the event; the remedial actions performed; technique; and follow on maintenance requirements. Contract maintenance was dispatched; normal inspections were conducted and logged; and the aircraft conducted its return flight to ZZZ. [Cause was] reacting to an unexpected profile or response by the system by attempting to rapidly diagnose settings and correct with autopilot. Seconds can be lost when quicker response to engage tcs and reorient isn't immediately executed.when faced with an unexpected and unusual response from automation; react immediately with manual control. Afterward; be extremely clear in detailing to the pm what was entered; what was received; and verify clarity of the situation in order to develop a most-conservative response and closer monitoring of possible human or automation factors at play. Trust the automation; but be prepared to verify any and all factors at play vs instinctively defaulting to experience and prior use and operation of the system.

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Original NASA ASRS Text

Title: ERJ-145 flight crew reported Autopilot failure on descent caused two overspeed occurrences resulting from extreme pitch down commands.

Narrative: On flight XXXX; ZZZ-ZZZ1; DATE; the crew experienced 2 high speed events during the descent into ZZZ1. While descending from cruise altitude it became necessary to expedite descent and slow the aircraft. As the PF; I retarded the throttles and extended the airbrake; configuring the aircraft for a 250 kt. descent. Upon doing so; the aircraft responded with an unexpected and unusual nose low attitude of approximately 15 degrees which caused rapid acceleration. The immediate reaction at that time was to retract the brake in order to clean the configuration of the aircraft and interrupt the pitch with TCS (Touch Control Steering) and pull carefully back into a less accelerative attitude. While the aircraft was being slowed; the highspeed warning annunciated and was active for approximately 8 seconds. The PM monitored the pitch and speed; and through proper coordination and manual control the aircraft was brought into a normal profile by disabling the previously selected SPD descent. After stabilizing the descent; the crew discussed the proximity to the airport and the relatively high altitude of the aircraft in order to proactively warn ATC of assistance. S Turns were requested and executed. During coordination with ATC and at approximately 12;000 ft I; the PF selected a FLC descent with speed brake to attempt to bring the aircraft through 10;000 with proper speed. The aircraft responded again with unusually steep downward pitch; and expecting this; faster action to apply TCS and reconfigure the aircraft for a hand flown descent was enacted by both crewmembers. Even with swift corrective action; the aircraft did accelerate to approximately 280 kts for a period of roughly 5 seconds. The approach and landing phases of flight were then safely executed without AP. After landing a normal shutdown was performed; AML entry was made; and the PM contacted Maintenance Control and described the event in detail. Afterward; the crew debriefed the event; the remedial actions performed; technique; and follow on maintenance requirements. Contract maintenance was dispatched; normal inspections were conducted and logged; and the aircraft conducted its return flight to ZZZ. [Cause was] reacting to an unexpected profile or response by the system by attempting to rapidly diagnose settings and correct with autopilot. Seconds can be lost when quicker response to engage TCS and reorient isn't immediately executed.When faced with an unexpected and unusual response from automation; react immediately with manual control. Afterward; be extremely clear In detailing to the PM what was entered; what was received; and verify clarity of the situation in order to develop a most-conservative response and closer monitoring of possible human or automation factors at play. Trust the automation; but be prepared to verify any and all factors at play VS instinctively defaulting to experience and prior use and operation of the system.

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.