B737-300
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 40
Distraction; Human-Machine Interface
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors; Procedure
While on the departure; we were initially given a 275 heading after departure from Runway 25. Sometime around FL200; we were given direct ZIMMR; on course. I punched ZIMMR into the FMC Page 1 Route page; executed it; and thought I hit LNAV. First Officer was making a PA at the time and I did not verify with him as I usually do. A few minutes later; ATC called and asked us if we were on a different arrival since we were about ten miles north of course. We said we were not and Controller cleared us direct MEEKER and we resumed the arrival. Controller stated that there was no problem and no conflict. [We had a] routine flight after that. I did not verify pressing LNAV because the First Officer was on the radio. I should have done it immediately after he got off the radio.
B737-300 Captain attributed a track deviation to his failure to engage LNAV on the FMS after loading a 'direct to' fix.