Beechcraft C90GT N508GT

The airplane climbed to 3,100 feet mean sea level (msl) on an approximate direct heading for the destination airport. When the airplane was about 9 miles east of the airport, the air traffic controller advised the pilot that he had "radar contact," verified the altitude of 3,100 feet msl, and instructed him to maintain visual flight rules (VFR). The airplane then descended to 3,000 feet msl, and, about 1 minute later, struck a communications tower with an overall height of about 3,089 feet msl. Examination of the airplane and engines revealed no evidence of any preimpact malfunction or failure that would have precluded normal operation. Review of the airplane's flight route indicated that the pilot had chosen a direct flight route near rising terrain and obstructions within a designated mountainous area at his selected cruise altitude of 3,100 feet msl, which was below the published maximum elevation figure of 3,500 feet msl depicted on the VFR sectional chart for the area. The pilot should have taken into account terrain elevation, obstructions, and weather when planning his route. If he had chosen a route that avoided obstructions and terrain and planned to fly at a higher altitude, he may have been able to safely complete the short flight. The airplane was equipped with a cockpit voice recorder (CVR) and an enhanced ground proximity warning system (EGPWS). The EGPWS had a terrain inhibit switch, which, when engaged by the pilot, inhibits all EGPWS visual and aural alerts and warnings to allow aircraft to operate without nuisance or unwanted warnings. However, the pilot's guide cautioned that the terrain inhibit switch should "NOT" be engaged for normal operations. CVR and EGPWS data revealed that the terrain inhibit switch was engaged before departure. As a result, although the EGPWS calculated an obstacle alert for terrain 3 minutes after takeoff, the alert was not annunciated. Review of previous flights revealed that the pilot routinely engaged the terrain inhibit switch while flying into the departure airport for this flight and would then disengage it after departure. This indicated that the pilot's normal habit was to disengage the terrain inhibit switch after departure, but, on this flight, his normal habit pattern may have been interrupted, he may have become distracted, or he may have simply forgotten to shut it off. Regardless, aeronautical charts found on board the airplane depicted the tower hazard, so the pilot should have had some awareness of the tower's presence. As noted previously, the controller identified the airplane and verified the observed and reported altitude. At the time that the airplane was identified, it was about 3.8 miles from the communications tower and its altitude was indicating that its trajectory was below the top of the tower. The tower's location was depicted on the controller's radar map as an obstruction to flight. Under the circumstances, the controller should have been aware that the airplane was flying 400 feet below the highest obstruction in the area and was nearing the tower, and he should have provided the pilot with a safety alert about the proximity of the antenna. Although the controller had other traffic, his workload at the time was not excessive. Although the weather conditions at the destination airport were conducive to landing under VFR, the pilot would have encountered reduced visibility and possibly instrument meteorological conditions east of the airport around the area of the accident due to haze and cumuliform-type clouds from 1,500 to 3,000 feet above ground level, which may have affected his ability to see the tower.

Quoted verbatim from the NTSB record.