Incident Overview
The pilot of an airplane requested and received clearance to execute a Simplified Directional Facility (SDF) approach. Air traffic control instructed the pilot to maintain 4,000 feet until established on the approach. Radar data showed that the airplane never became established on the approach and began descending before reaching the Initial Approach Fix (IAF). The airplane crossed the IAF at 2,900 feet and continued in a descending left turn into unprotected airspace.
Radar and Flight Path
The airplane disappeared from radar at 1,900 feet as it completed 180 degrees of turn. The turn did not correspond to any of the four instrument approaches to the airport. The airplane subsequently struck a guy wire on a lighted communications antenna located 3.3 nautical miles southeast of the airport on a heading of 360 degrees.
Mechanical and Navigation Findings
No evidence of a mechanical failure or malfunction of the airplane or its systems was found. A flight check conducted by the Federal Aviation Administration (FAA) confirmed that no navigation signal was received for the approach. The approach had been turned off and listed as out of service for over four years. The pilot did not report the lack of a navigation signal to air traffic control and did not execute a missed approach.
Air Traffic Control Factor
Interviews revealed that the air traffic controller failed to verify that the approach was in service before issuing the clearance to the pilot.
Probable Cause
The failure of the pilot to follow his approach clearance, and subsequent descent into unprotected airspace which resulted in a collision with the guy wire. Factors were the failure of the air traffic controller to verify the approach he cleared the pilot to conduct was in service, and the clouds which restricted the visibility of the communications antenna.