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.

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Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.