B737-800
Flight Crew Last 90 Days 183
Situational Awareness
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation
Aircraft; Human Factors; Procedure
Arrived at aircraft 10 minutes prior to scheduled push. There was absolutely NO pressure by ZZZ Ground Ops. We took our time and completed preflight normally. ZZZ was IMC; 400 OVC/2.5 NM Vis/Rain. All ground ops/engine start/taxi were normal. MAX PWR T/O with flaps set at 25. Takeoff was normal. Turned to assigned heading of 140 degrees and began retracting flaps on schedule. At approximately 2;400 feet MSL; the Auto Throttle (A/Ts) began retarding power fairly rapidly; I believed in anticipation of the 3;000 feet level off. Flaps were positioned to 5; and the airspeed began to bleed off; and would not accelerate above the flap 5 MASI speed. N1 was approximately 76%.I began pushing the power levers against the A/Ts. Aircraft began to sink. Ground Proximity Warning System (GPWS) responded with two 'Don't Sink' calls. Airspeed was still bleeding off (lowest seen was approximately 191 KIAS). I disconnected the A/Ts and called for and applied full power. At this time; GPWS gave a 'Too Low Terrain' call. A/S increased with the power addition; descent was arrested; and we began to climb. Retracted flaps on schedule and resumed departure. Aircraft did exceed the MASI UP speed below the Class B airspace. The aircraft did not descend below 2;000 feet MSL. ATC never queried or questioned anything.From my perspective; it is sort of the perfect storm. Max PWR; Flaps 25 T/O; IMC; Midway Departure leveling at 3000; which comes quickly with a MAX PWR T/O. Turning; climbing; IMC; flap retraction; scheduled departure with a fairly fast hand-off to ATC. The Flight Crew is very busy. With the A/Ts engaged; they are going to pull back fairly quickly due to the 3;000 feet level off especially given the robust rate of climb with a MAX PWR T/O. The aircraft may not (as with us) accelerate to the flaps 5 MASI speed or more unless the Pilot Flying pushes up the power. Bottom-line is you need to be ready when the aircraft begins to approach level off and the A/Ts start to retard. Need to kick them off if the aircraft is not accelerating as you need it to. Given these circumstances; the flight crew is in the Yellow taking the runway. We found ourselves in the Red at 2;400 MSL. This is simply a case of understanding the automation and anticipating how it will respond to a given situation. The flight crew needs to be ready to change the state of automation; in this case turning off the A/Ts; and allow the aircraft to continue to accelerate to the MASI UP speed. It happens fast.
B737-800 Captain reports departingusing maximum power and flaps 25 to a 3;000 foot level off. The auto thrust reacts aggressively to the approaching level off resulting in loss of airspeed and altitude and EGPWS warnings for 'Don't Sink' and 'Too Low Terrain'. Auto thrust is quickly disconnected and full thrust applied to recover.