B737-700
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 459; Flight Crew Type 459
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft; Human Factors; Procedure
The aircraft had the Autothrottle System MEL inoperative. Center assigned a speed of 300 kts or greater; and direct to ZZZZZ waypoint. Upon handoff to [Approach]; we were then cleared the ILS XXR; and 2;200 feet was set in the MCP Altitude window. At the deceleration point to slow to 270 kts; the aircraft pitch adjusted nose up; but not enough; and the aircraft descended below the VNAV PATH and the lower crossing restriction of 12;000 feet prior to reaching ZZZZZ1.VNAV disconnect occurred and the Vertical mode reverted to CWS (Control Wheel Steering) pitch. The PF (Pilot Flying) intervened with Vertical Speed mode; and set 10;000 feet; in the altitude window for the next crossing restriction. Due to the autothrottles being inoperative; the thrust remained at idle the whole time; [there was] also negative turbulence during the descent. After passing ZZZZZ1 the VNAV PATH was re-joined with MCP VNAV mode; no further deviations during the descent. I was more focused on the magenta descent path deviation and the VNAV disconnect rather than the actual aircraft altitude; which caused me to be slow to react. Also I would like to add that other than the 300 kt speed assignment; there was nothing unusual and the autopilot should not have missed that altitude.
B737 First Officer reported deviating from altitude restrictions during descent to land.