B737-300
Flight Crew Last 90 Days 108
Distraction; Human-Machine Interface
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Aircraft; Human Factors
[I] departed on a 030 heading to avoid weather east of the field. After clearing the weather; we were cleared to our next point; FORPE. I selected the point; moved it to the top of the LEGS page; confirmed with the First Officer; and executed and then selected LNAV. The aircraft turned to FORPE and was on course. During the climb; I wanted to get out the arrival for review and I was heads down for longer than usual because the arrivals were incorrect in chart manual. When I crosschecked the NAV instruments; I saw that the aircraft had passed FORPE and the LNAV was no longer engaged. I immediately turned back to course and asked the First Officer to inform ATC of our situation at which point ATC asked where we were going. We informed them of our system disconnect and they gave us a short vector to get back in position. We discussed the event and noted that we did a proper preflight brief and departure brief and everything was set up correctly. The aircraft simply had a hiccup and unfortunately it got us when we were distracted by another issue.
B737-300 Captain experiences a track deviation after being cleared direct to a waypoint and selecting LNAV. LNAV did not engage or dropped off after selection and was not detected by the crew until after the waypoint had been passed.