Cessna 210F N1842F accident near Pleasanton, California

Probable cause

The pilot’s continued visual flight into instrument flight rules conditions, which resulted in his failure to maintain sufficient clearance from rising terrain.

NTSB analysis

Before beginning the cross-county flight under visual flight rules (VFR), the pilot received a weather briefing that reported VFR conditions at the departure and destination airports but included an airmen's meteorological information notice for instrument flight rules (IFR) conditions along the route of flight. About 8 minutes after departure, recorded radar data showed the airplane's altitude varying between 321 and 635 ft above ground level (agl) for about 1.5 minutes before the impact. Until about 30 seconds before impact, the airplane was tracking south on course along a valley, but it then began to deviate west toward rising terrain. The airplane then began a slow, descending right turn. The last recorded radar target showed the airplane about 0.2 miles from the accident site, at an altitude of about 410 ft agl.

A postaccident examination of the airframe and engine revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. A review of weather observations and satellite imagery indicated that IFR conditions prevailed in the vicinity of the accident site due to low clouds and restricted visibility. It is likely that the pilot was varying his altitude to remain clear of the clouds and subsequently entered an area where continued flight on course was not possible and initiated a right turn. During the turn, the airplane collided with rising terrain.

Text from the NTSB. Open the NTSB docket for WPR15FA166 for the full record.