Flight Crew Last 90 Days 199; Flight Crew Type 9000
Human-Machine Interface; Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
On descent on the SWFFT TWO Arrival into BNA; we were given a descent to FL350 from FL390. We did a cruise descent; selecting FL350 on the Cruise page. As the aircraft was leveling at FL350; Center gave us a further descent to FL300. MCP to FL300; but Altitude Intervention was not pushed. The aircraft leveled at FL350. About three minutes later; Center asked if we were descending; at which point the First Officer selected V/S and expedited to FL300.  There were no traffic conflicts. I need to verify not only the altitude but that the autopilot does what we are commanding and expecting. I was confident in my First Officer because he was doing such a good job.
B737-800 Captain reports being cleared to FL350 from FL390 then cleared to FL300 as the autopilot is leveling at FL350. The MCP altitude is reset to FL300 but the descent is not reinitiated and the aircraft remains at FL350 until queried by ATC.