Flight Crew Last 90 Days 240; Flight Crew Total 12000; Flight Crew Type 3000
Time Pressure; Fatigue; Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Flight Crew FLC Overrode Automation
Procedure; Weather; Human Factors; Aircraft
We were approaching Orlando thru an area of multiple thunderstorms. The final Approach Controller was very busy and you could hear he was a bit tense. We were approaching the inbound localizer course for 17R at 6;000 FT which was 2;000 FT high since we were just outside ONNER Intersection. My copilot was trying to get a request in for lower; but the frequency was congested. As we approached at 6;000 were were getting higher by the minute. We finally were cleared to 4;000 ft. I selected FLCH  4;000 FT with full speed brakes. Shortly after we were cleared to maintain 4;000 till established on final cleared for the approach. I was in Flight level change descending from 6;000 to 4;000 when given the ILS approach clearance maintain 4;000 till established. I wanted to set up LAVS to the feather; so we would comply with the next two fixes HAMMY (3;000 FT)  & TUFFE (2;200 FT)  I selected LOC; Altitude to 200; VNAV; Speed. The VNAV did not engage. As I was focused on the LAVS setup the ac had just descended below 4;000 FT; so VNAV would not engage. We descended to about 3;700 FT and I hand flew the correction and approach. The weather was VFR. We landed without incident. In retrospect Using VNAV initially would have been a better choice considering the timing of clearance and aircraft rate of descent. Also FLCH would have worked also if I continued using it and not changing to VNAV. Changing methods of descent from FLCH to VNAV in such a time compressed event is not a good idea
When ATC held them high and then cleared them for the approach while still descending at a rapid rate; the pilot flying of a B737 elected to use FLCH and full speed brakes to attempt to get on profile. When utilizing the 'LAVS' procedure (Lateral nav mode/Altitude to which descending/Vertical navigation mode/airSpeed) to configure avionics for the approach VNAV was selected but; due to the high rate of descent; they had already passed through the last useable crossing restriction and; thus; VNAV would not engage. In VMC at the time; they then disconnected the automation and landed without incident.