Friday, 3th of January, 1992

– United States of America

CommutAir Flight 4821, a domestic scheduled passenger flight from Plattsburgh-Clinton County Airport, NY (PLB/KPLB), to Saranac Lake-Adirondack Airport, NY (SLK/KSLK), operated with a Beechcraft 1900C-1, registration N55000, impacted wooded terrain while on approach about 8 km (5 mls) northeast of Saranac Lake-Adirondack Airport (SLK/KSLK), New York.

The airplane was destroyed. The First Officer and one passenger were fatally injured. The Captain and the remaining passenger survived with serious injuries. (2 fatalities, 2 survivors)

– Details:

On IFR arrival, flight 4821 was cleared to intersection 17 northeast of airport at 6,000 feet, then for ILS runway 23 approach. Radar service was terminated 6.5 east of intersection. Radar data showed that flight crossed and then bracketed localizer. Flight intercepted glide slope from below about 7 miles outside of outer marker and thence deviated above glide slope. About 2 miles outside of marker, flight was at a full fly down deflection when it entered a descent varying from 1,200 to 2,000 fpm. Aircraft struck wooded mountain top 2.0 miles inside of outer marker (3.9 miles from runway) at elevation of 2,280 feet. Minimum altitude at marker was 3,600 feet. Glide slope elevation at point of impact was approximately 2,900 feet. Evidence was found of inadequate electrical ground path between radome and fuselage which, when combined with existing weather conditions, may have produced electrostatic discharge (precipitation static). Although post-accident tests were not conclusive, the safety board believes that the glide slope indications might have been unreliable due to precipitation static interference. Two occupants survived while two others (one pilot and one passenger) were killed.

– Cause:

“Failure of the captain to establish a stabilized approach, his inadequate cross-check of instruments, his descent below specified minimum altitude at the final approach fix, and failure of the copilot to monitor the approach. Factors related to the accident were: weather conditions and possible precipitation static interference, caused by inadequate grounding between the radome and fuselage that could have resulted in unreliable glide slope indications.”