B737 Undifferentiated or Other Model
Flight Crew Last 90 Days 109
Confusion; Fatigue; Workload
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Human Factors
We were flying the Arrival. [Approach] assigned us the FMS VISUAL. As the Pilot Managing (PM); I loaded the approach into the FMC. The First Officer (FO) verified it and I executed it. After [a] waypoint; the aircraft stayed on a 240-degree course (in LNAV). ATC brought this to our attention.As a crew; we discussed this after we landed and we still do not understand where we made a programming error. There are a few factors that contributed to me not intervening and manually putting the aircraft on the correct course immediately; and they are; we were both tired; day three of a four-day trip; and it was the last leg. Another factor; I briefed my FO at the beginning of the day to remember we do not have autothrottles. We were in an older model aircraft! It is my personal observation that comfort to autothrottles is a growing issue; especially when it gets busy on the flightdeck. On this leg; I had to remind the FO a few times about not having autothrottles and that we were getting slow. In fact; I had to intervene twice and adjust the throttles myself. My final factor was that my headset broke on day two. It would not transmit. I used the headset for receiving and the hand MIC for transmitting. This increased my workload.
A B-737 flight crew; on approach; failed to detect that their aircraft; while in LNAV; took up a heading instead of sequencing to the next waypoint on the arrival. The Captain thinks there may have been a programming error. He attributes the failure to detect was due to the crew's fatigue caused by high workload.