What happened
A flight originating from Burbank, California, was scheduled to visit both Oakland and Sacramento. After departing Oakland at 16:56, the aircraft, an unnamed model, carried six passengers and a crew of three. The total weight and load distribution were within certified limits, and the aircraft possessed enough fuel for a duration of two and a half hours, well exceeding the expected thirty-minute flight time to Sacramento.
Shortly after takeoff, the flight maintained a position five miles northwest of Oakland Airport for approximately seven minutes while awaiting instrument flight clearance for an altitude of 4,000 feet. At 17:08, the crew reported being over the Richmond Radio flange Intersection, located 16 miles northwest of Oakland, and provided an estimated time of arrival at the Fairfield Radio flange Station.
Because the crew did not explicitly state their current altitude during this transmission, Air Route Traffic Control requested clarification. The flight responded that they were maintaining 4,000 feet; this was the final communication from the aircraft. About one hour after the position report near Richmond, authorities received notification that the plane had crashed six miles east of Vallejo. The impact resulted in all nine occupants being killed and the total destruction of the aircraft.
Findings
The investigation concluded that the accident occurred because the flight was not maintaining its assigned altitude while operating under an instrument flight plan, leading to a collision with a hill that was hidden by cloud cover.