What happened
During an instrument flight rules (IFR) arrival, the crew of flight 4821 was cleared to an intersection located northeast of the airport at 6,000 feet, with instructions to proceed to an ILS runway 23 approach. Radar services were ended approximately 6.5 miles east of the designated intersection. Radar tracking indicated that the aircraft crossed and subsequently bracketed the localizer.
As the aircraft intercepted the glide slope from a position below the path roughly 7 miles before the outer marker, it began to deviate above the glide slope. Approximately 2 miles from the outer marker, the aircraft was positioned at a full fly-down deflection and entered a descent rate between 1,200 and 2,000 feet per minute. The aircraft type struck a wooded mountain peak at an elevation of 2,280 feet, located 2.0 miles inside the outer marker and 3.9 miles from the runway. At the time of the impact, the minimum altitude at the marker was 3,600 feet, while the glide slope elevation was approximately 2,900 feet.
The accident resulted in two fatalities and two survivors.
Findings
Investigators identified an insufficient electrical ground path between the fuselage and the radome. Under the prevailing weather conditions, this deficiency may have caused electrostatic discharge, also known as precipitation static. While post-accident testing did not provide definitive results, the safety board concluded that precipitation static interference may have rendered the glide slope indications unreliable.