Date: 201210
Local time of day: 0601-1200
Location: ATL.Airport, GA
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Climb
Airspace: Class B ATL
ATC / advisory: TRACON A80
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Human Factors

Narrative: We took off from Runway 8R in Atlanta on the GEETK 6 Departure. We were sequenced behind a [Company aircraft]. I was the Pilot Flying. After liftoff; a course of 092 was followed until 400 FT when LNAV was called for and selected. At approximately this same time; we entered some wake turbulence from the preceding aircraft. We continued to climb out and contacted Departure. Very shortly thereafter; the Departure Controller asked us if we were headed to HRSHL which was the first fix we would turn on the departure (69 degrees). A very hurried glance showed that the LNAV was not engaged and we were still following the heading of 092. The Controller immediately issued vectors and said there was a possibility of an aircraft conflict. We immediately replied we were having FMS issues and he said we should have let him know sooner. Since we were unaware of the problem to begin with; there was no way of being able to advise sooner. We continued to receive vectors on course and advised the Controller the FMC was working properly. After a few minutes we were switched to Center and given a phone number to call upon our arrival. I talked with Atlanta Tower and gave them a description of the problem. He said they were documenting it as an RNAV anomaly and that we would not hear from them again. I do not remember verifying that the LNAV had been engaged because; as the pilot flying; that was the time that we started to encounter the wake turbulence and my attention turned to that. It was a big mistake at a very busy airport. We both needed to be more vigilant.


Second narrative: After takeoff; we encountered wake turbulence from the preceding aircraft. The Captain (pilot flying) called for LNAV. I (pilot not flying) pushed the LNAV button but it failed to engage. The Captain noticed we over flew the first turn (to HRSHL). I started to program the FMS when ATC queried why we were not turning. I inadvertently put GEETK as the first fix thus erasing all the previous fixes. Given the circumstances of the event (gear up; wake turbulence; LNAV button and first turn) there was not much room for error. Fortunately; there was no conflict with any other traffic.


Synopsis: On departure from ATL a B737-700 flight crew encountered wake vortex and then failed to engage LNAV which caused a deviation from the departure track.