B737-700
Human-Machine Interface; Workload; Troubleshooting; Situational Awareness; Confusion
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft Automation Overrode Flight Crew; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Aircraft
We were given a descend via clearance on the arrival with a runway assignment. On descent; we were given the option of landing on 36L; a more favorable runway. I programmed in the new runway and briefed the approach. I extended out the approach to a waypoint that was higher than the lowest point on the arrival. The FMC didn't like this and it took a little while to identify that this was the problem. After it was corrected; we finished the Descent Checklist. I realized that the aircraft was not descending correctly on the arrival. When I had selected a new runway; the FMC put the arrival back in but with a discontinuity as the next waypoint. As a result; the aircraft didn't know where it was on the arrival. I then selected Level Change to get the aircraft back onto VNAV PATH. I believe the crossing restrictions at both MRCEL and DASAC were missed. Approach Control then gave us an unrestricted descent to 3;000 FT. This occurred at a very busy time on the arrival. We started the Descent Checklist; changed runways; tried to correct an altitude problem on the approach; returned to the Descent Checklist; and then realized we were not on VNAV PATH. After reprogramming the new runway; the FMC responded in an unanticipated way. I did not monitor the automation to the level that it required.
The reporter is not certain at exactly what point the FMS transitioned; nor to what BLUZZ 1 RNAV waypoint it wanted the aircraft to turn. Because the event was unexpected; after the event both pilots were task saturated attempting to comply with arrival constraints. He believes the transition occurred after BLUZZ but before LTOWN. The reporter is certain that the trigger was entering the runway change and he thinks the next FMC waypoint was then behind them. He remembers the Mode Control Panel indications were very odd and believes he saw Control Wheel Steering Roll and VNAV SPD; but the speed mode is a guess. He is the FMC disregarded the MRCEL and DASAC waypoint altitude constraints.
After a B737-700 First Officer flying the MEM BLUZZ 1 RNAV changed landing runways the FMC put the arrival back in but with a discontinuity at the next waypoint; disconnected VNAV and caused the aircraft to miss at least two crossing restrictions.