Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 113; Flight Crew Type 1259
Situational Awareness; Human-Machine Interface
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented
Aircraft; Human Factors; Procedure
On arrival on the TELLR2 Arrival; 10 miles prior to CRAGG ATC requested us to slow to 210 KTS and then expedite to 10;000. The Captain slowed to 210 and then expedited to 10;000 by switching from VNAV to LVL CHG. Shortly after we were cleared for the approach. I put 7;000 in the MCP for the FAF altitude at CORDE. At approximately 9;700 feet I noticed we were below the published minimum altitude of 10;000 and advised the Captain. At 9;300 feet he started a climb back to 10;000. The error we made was not going back into VNAV after being cleared for the approach.
Neither of us noticed being out of VNAV and we descended to 9;300 feet before we changed the altitude back to 10;000 which was the minimum altitude prior to our next fix.
Air carrier flight crew descended below a STAR published minimum altitude due to being in FMC LVL CHG rather than VNAV mode.