B737 Undifferentiated or Other Model
Flight Crew Last 90 Days 125
Troubleshooting; Situational Awareness; Human-Machine Interface; Workload; Distraction
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Aircraft Automation Overrode Flight Crew; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Aircraft; Procedure
We had loaded the RNAV Arrival with a landing on 16L into the FMC. We did not close the route discontinuity between the arrival and the 16L ILS as per Company procedures. Center gave us numerous speed changes for sequencing and finally vectored us off the arrival. We were eventually told to rejoin the arrival at a specific waypoint and told to descend via the RNAV. We were also given yet another speed change. The flying Pilot was doing a good job of complying with the numerous speed and altitude changes. We were handed off to Approach who assigned us to descend via the RNAV Arrival landing Runway 16R. Since the Pilot Flying was task saturated just flying the arrival; I elected to change the landing runway in the Arrival page by selecting the ILS 16R approach. With the RNAV Arrival selected; changing the landing runway should not have impacted this arrival and waypoint sequencing since we were not changing the direction of the landing runway; for example; 16 Left versus 34 Right. I did fail to review the change on LEGS page 1 before executing. When I did execute the change; the aircraft started a turn back to a waypoint behind us. We immediately disconnected the LNAV while I tried to bring the next active waypoint to the top of the LEGS page.We did leave the route so Approach sent us direct another waypoint and told us to descend to 15;000'. Established on the arrival; we experimented without executing to see if the FMC would do that again. We selected Runway 16 Left on the Arrival page and noted a discontinuity at the top of the LEGS page; once again to a waypoint behind us. I hit 'Erase Line Select' and we continued normally to a landing on 16 Right.
A B737 Captain noted that while flying a programmed RNAV Arrival; he changed the landing runway; selected EXEC and the FMC reprogrammed itself to a waypoint behind the aircraft. After reestablishing on the RNAV Arrival he verified his actions with the same result.