Accident Sequence
The pilot departed on a scheduled flight under night instrument meteorological conditions. Arriving near the destination airport, the reported weather included winds from 220 degrees at 18 knots, gusting to 25 knots; 1/2 statute miles visibility with haze; and vertical visibility of 100 feet. The pilot was vectored and cleared for the ILS 24 approach. As the airplane crossed the glideslope, the ride became increasingly bumpy and turbulent with a strong wind component from the right. The approach lights appeared as the airplane neared the runway but soon disappeared due to low visibility. The pilot executed a missed approach; as full power was applied, the airplane began moving laterally to the left. During the missed approach, a "thunk" was heard on the left side of the fuselage, and the airplane descended into trees. It came to rest in a wooded area about 1/4 mile from the Runway 24 threshold, approximately 1,000 feet left of the extended centerline.
Weather and Conditions
The weather reported at the destination airport during the approach was: wind 220 degrees at 18 knots, gusts to 25 knots; visibility 1/2 statute miles in haze; vertical visibility 100 feet. The approach was conducted under night IMC.
Glideslope Tracking
Review of the approach plate for the ILS 24 approach indicated the glide slope altitude at the final approach fix (about 4 miles from the runway) was 1,407 feet, and at the middle marker (about 0.6 miles from the runway) was 299 feet. Radar data showed the airplane intercepted the glideslope about 4 miles from the threshold. In the following 2 minutes 30 seconds, the airplane deviated below and returned to the glideslope centerline approximately 4 times, with a maximum deviation of 2 dots below centerline. About 1 mile from the runway, the airplane began a downward trend from the glideslope centerline, descending below the 2-dot low deviation line to about 300 feet, when the last radar hit was recorded. During the approach, ground speed varied between 50 and 125 knots. The Aeronautical Information Manual section on ILS advises pilots to "Make every effort to remain on the indicated glide path" and "Avoid flying below the glide path to assure obstacle/terrain clearance is maintained."
Probable Cause
The official probable cause was the pilot's failure to maintain a stabilized approach with an adequate vertical and lateral track. Also causal was his failure to maintain obstacle clearance.