Date: 202102
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
Aircraft component: Autothrottle/Speed Control
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Human-Machine Interface; Confusion; Troubleshooting
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; Flight Crew Overrode Automation
Contributing factors: Aircraft; Weather
Primary problem: Ambiguous

Narrative: On initial climbout of ZZZ off Runway XXC we experienced loss of power shortly after passing 400 feet and received the 'Landing gear' aural warning. I double checked the gear handle and verified gear position; then verified N1 rollback; momentarily thinking we had dual engine failure. FO exclaimed startle; I replied 'fly the plane'. FO disconnected auto throttle; brought the thrust back up to takeoff position. We momentarily lost altitude and airspeed as Startle and surprise delayed our recognition slightly. Timing of the event was before flap retraction so we were near flap over speed during recognition and recovery; I said 'watch the speed pitch up pitch up' until flaps were retracted. FO later indicated his flight director was not giving correct indications for phase of flight. FO was able to recognize and manually control the aircraft; resuming normal climb out. Once the aircraft was under control; auto pilot and auto throttle engaged normally and no further anomalies were experienced.Unknown; weather was stormy; with moderate turbulence and lightning flashes in vicinity; in full IMC.We teach hand on thrust levers at all times during arrival and landing phase; but not during takeoff...had the FO had physical contact with the thrust levers during the climb; the AT retarding would have been instantly detected. I recommend the same procedure is taught for takeoff as is for landing...one hand on the thrust levers.


Second narrative: After checking everything was normal we lined up on runway XXC in ZZZ. We verified our automation was in the correct mode including TO; ROLL; and FLCH were verified on our FMA as well as the crosshair flight director was up. As I advanced thrust the auto throttles took and the captain confirmed that ATTCS armed and we had normal TO thrust. at 80 knots while verifying the speed I saw the AT were in their normal HOLD mode. At this point everything was completely normal. When I went to rotate and was transitioning in the instruments I noticed that the FD had switched during the roll to the diamond mode which is supposed to happen at 1000'AGL. (Latter the captain confirmed that there's was normal). I had a normal rotation and pitched towards a normal takeoff attitude disregarding the flight director. At approximately 400 AGL the auto throttles commanded idle thrust suddenly. The startle and surprise nature of this took a second to process where we lost approximately 50 feet. At this point I disconnected the auto throttles and set climb power. The automation was still not working correctly including the flight director. Once we climbed through sterile we turned on the auto-throttles and they worked throughout the flight but we watched them very carefully and called Maintenance writing up the experience on the ground. The cause is unknown. before Takeoff we both verified we were in the correct automation modes. Once in cruise flight we verified all out take-off date and departure limits were set correctly and they were. Contributing factors to the loss of altitude was the thunderstorms in the vicinity; night; and moderate turbulence. More effective startle and surprise training in the sims. We are taught to keep both hands on the yoke throughout departure I think at 400 feet though 10;000 we should be guarding the thrust levers like we do on approach to landing.


Synopsis: EMB 170/175 flight crew reported a momentary loss of control and altitude when the autothrottles (AT) went to idle thrust just after takeoff. The crew disconnected the AT; regained control; and continued the flight.