Date: 202007
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: VMC
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Troubleshooting
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew FLC Overrode Automation; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

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.


Second narrative: While on the descent into ZZZ the crew experienced two (2) highspeed events. The flight descended from their cruise ALT of FL160 to FL 110 at 300 kts to begin the arrival. When ZZZ Approach cleared them from 11;000 ft to 3;000 ft the PF retarded the throttles; selected 250 kts; extended the speed brakes; selected 3;000 ft in the ALT; and selected IAS. The aircraft pitched down aggressively; and the aircraft accelerated rapidly. The PM was on the radio requesting S-Turns to assist in losing altitude and had programmed the FMS to activate the RNAV approach. At 10;500 ft the PM noticed that the speed was accelerating towards the redline and instructed the PF to slow down by depressing the TCS (Touch Control Steering) button and pitching the aircraft up to bleed off speed. The PF retracted the speed brakes; TCS the controls steadily and smoothly; however; the airspeed continued to increase; and the speed reached 270 or 280 for less than 10 seconds. Once the airspeed was below 250 kts the PF released the TCS button and the aircraft pitched down aggressively and received the highspeed warning and the speed reached 260-270 for less than 8 seconds. The PF depressed the TCS button and pitched up again to slow down. Once the speed was below 250 kts the PF turned off the AP; selected VS 1800 fpm; and completed the VIS APPCH without further incident. Upon arrival at the gate and after the shutdown checklist the crew contacted Dispatch and Maintenance and described what had occurred. The Captain made an AML entry and Maintenance contacted contract maintenance to complete the overspeed checklist and download the DFR. When Maintenance completed the inspection and closed out the AML the return flight to ZZZ1 operated without further incident.The crew began a descent from 11;000 ft to 3;000 ft prior to slowing the aircraft to <250 kts.Ensure that the aircraft is at the proper speed and configuration for each phase of flight. Stay ahead of the aircraft by planning your descent from cruise to transition 10;000 ft. at the proper speed.


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