B757-200
Flight Crew Air Transport Pilot (ATP)
Fatigue; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors
IOE event for PF..Me.. Inbound to FNT; RNAV GPS RWY 36; had planned for ILS 27 switched to RNAV approach with Flint Approach.  Received late vectors to join approach at Cokin Intersection; high and fast to begin approach; selected flight level change; speedbrakes fully deployed; speed 240kts; started approach; missed LAVS procedure on selecting VNAV; dialed down to 800 feet; LNAV; speed; very busy monitoring radios and course; aircraft intercepted lateral course in a turn to final.  Level change took us low; by 200 feet; we recognized it and went autopilot off; added power; speed brake retracted; leveled off and climbed back to altitude.  At the same time; Flint approach issued a 'low Altitude Alert'.  During this whole event we were in VMC conditions and had the field in sight at 10 miles. Continued visually and executed a normal landing.We were rushed getting everything done for the approach.  I also have a total of 15 hours in type; so this approach change at 0500 was difficult. We should had continued with our original plan of ILS 27 and not asked for the RNAV approach.  We made ourselves rush into a mistake.
When we crossed Cokin we inserted HAT (Height Above Touchdown) of 800 FT into the ALT window. Passing 2200 we realized we were low and were making a correction when ATC called use concerning the low alt alert. We climbed back up to VNAV path and continued approach to an uneventful landing. When trying to figure out how we got below VNAV path; that is when PF told me about switching to FLCH. It was debriefed.
B757-200 flight crew reported getting a low altitude alert from ATC on approach to FNT and realized they were in FLCH mode and had descended below procedure altitude.