Amateur-built STOL CH701 N4209W accident near Marienville, Pennsylvania

Probable cause

The pilot’s decision to continue visual flight into deteriorating visibility conditions at night, which resulted in spatial disorientation and subsequent descent that continued to ground contact.

NTSB analysis

Prior to departing on the night visual flight rules (VFR) flight, the non-instrument-rated pilot accessed a flight planning application to plot a route for the cross-country flight, but did not obtain a weather briefing, nor did he obtain a weather briefing from any other flight service provider. ADS-B data showed the pilot departed and established the airplane at an altitude of about 3,100 ft mean sea level (msl). Weather reporting along the route of flight showed the airplane flying through areas of cloud cover with bases ranging between 1,700 and 3,300 ft msl, and a weather model estimated that cloud bases were about 3,000 ft msl near accident site around the time of the accident.

About 90 seconds before the last recorded ADS-B data, weather radar indicated that the airplane, flew into an area of developing light snow. About this time, the airplane began a left turn while flying at 2,900 ft msl. The left turn tightened, and the airplane climbed to about 3,350 msl, before it entered a steep descent in a tight left spiral. The airplane then impacted trees and terrain. Postaccident examination of the airplane revealed no evidence of any preimpact mechanical malfunctions or failures that would preclude normal operation.

The circumstances of the accident—visual flight in dark night lighting conditions under an overcast cloud ceiling into an area of deteriorating visibility due to snow by a non-instrument-rated pilot, which culminated in a steep, turning, un-arrested descent—are consistent with the pilot experiencing a form of spatial disorientation known as the somatogyral illusion or graveyard spiral. After encountering the reduced visibility conditions, the pilot likely did not perceive that the airplane was turning and pulled back on the flight controls, tightening the spiral and increasing the descent rate, which ultimately continued to ground contact

Postmortem toxicological testing indicated that the pilot had used methamphetamine, which has substantial potential to result in impairment. The degree to which the effects of methamphetamine contributed to the pilot’s decision to continue visual flight into deteriorating visibility conditions at night, could not be determined with certainty.

Text from the NTSB. Open the NTSB docket for ERA24FA077 for the full record.