B737-700
Flight Crew Last 90 Days 204
Human-Machine Interface; Situational Awareness; Confusion
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification
Aircraft; Human Factors; Chart Or Publication
After taking off Runway 25R; the aircraft was tracking LNAV on course. The aircraft turned to the south on course and ATC assigned us a climb unrestricted to 19000 feet. Aircraft went into HDG mode unnoticed. ATC asked us shortly after if we turned early to go direct to BOACH. We realized the aircraft was in HDG mode. ATC said we were the fourth aircraft that night that did the same thing.
[Report narrative contained no additional information.]
B737NG Pilot reported the aircraft navigated off course on its own.