WPR09LA263 · Lanham Lancair IV

Seventeen hours before departing for the cross-country flight, the pilot received a weather briefing; no other weather updates by the pilot were identified prior to departure and filing of the instrument flight plan. AIRMETs current for the time and area of the accident flight forecast mountain obscuration in clouds and moderate icing conditions between 12,000 and 25,000 feet. The pilot’s assigned altitude was 21,000 feet, and radar data indicated that the airplane was cruising at 20,900 feet with varying altitudes of plus or minus 100 feet for about 25 minutes. A few minutes before the accident, the air traffic controller issued the pilot a clearance to descend from 21,000 feet to 16,000 feet, which the pilot acknowledged. Radar data showed that the airplane descended rapidly, transitioning from a recorded altitude of 20,400 feet to 17,200 feet in 32 seconds, followed by an altitude of 13,700 feet (the last recorded radar target) 8 seconds later. The accident site was located at an elevation of 5,800 feet.

On-site documentation indicated that the airplane impacted the ground in a right-wing-low attitude with a debris path that extended about 100 yards from the first identified point of impact. The airframe was heavily fragmented, and only a limited examination could be accomplished due to impact damage. The engine was also severely impact damaged; however, examination of the available components revealed no evidence of abnormalities that would have prevented normal operation. Based on the available weather data for the area of the accident flight, it is likely that the flight encountered the forecast icing conditions. Moderate intensity icing is defined as a rate of accumulation such that even short encounters become potentially hazardous, and the use of deicing and anti-icing equipment or diversion is necessary. The airplane was not equipped for flight in icing conditions.

Verbatim NTSB analysis and probable cause from the NTSB dataset