N893MK - 2000 Aircraft Aircraft Registration

The pilot's failure to maintain the course for the published approach procedure due to his diverted attention. The distraction responsible for the pilot's diverted attention was the erroneous frequency assignment provided by ATC and the resultant task overload induced by this problem and the confusion surrounding the ATC clearances to get established on the final approach course, which likely involved repeated reprogramming of the navigation system. Factors in the accident include the failure of ATC to provide the pilot with a timely and effective safety alert concerning the deviation from the proper course, which was influenced in part by the features of the radar display at both facilities which made the deviation more difficult to detect, and the nature of radar as a secondary tool for a VFR tower controller. An additional factor was the nonstandard method of providing approach clearance, which likely may have exacerbated pilot task overload.