What happened
On August 24, Flight 615 was operating under an instrument flight plan from Chicago to Oakland, with a subsequent leg planned to San Francisco. The aircraft was traveling via several airways, including Red Airway 4 and Green Airway 3, and was cleared to descend to 6,000 feet as it approached the Newark, California area. During the descent, the crew communicated regularly with Air Route Traffic Control, reporting their position over Stockton at 9,500 feet and later passing the Altamont Intersection.
As the flight neared Oakland, the pilot requested a straight-in range approach to the Newark fan marker. Approach Control granted this request, instructing the aircraft to maintain an altitude of 500 feet above the cloud tops between Altamont and Newark. After briefly requesting an ILS approach and then canceling that request, the aircraft was cleared for a straight-in approach on the southeast course of the Oakland radio range. The final radio transmission occurred at 0427, with the crew reporting they were leaving Newark inbound to Oakland.
Shortly after this contact, the four-engine aircraft collided with Tolman Peak, which has an elevation of 985 feet, located approximately 14.6 miles southeast of the Oakland airport. The impact destroyed the aircraft, and there were 50 fatalities in the accident.
Findings
Investigation into the crash determined that the primary cause was the pilot's failure to follow established instrument procedures while conducting an approach to Oakland Municipal Airport. Specifically, the captain did not adhere to minimum altitude requirements for the Newark area during the descent. Additionally, it was noted that neither radio receiver on the aircraft had been tuned to the Oakland radio range station as required by the procedure. At the moment of impact, the aircraft was flying at an altitude of 983 feet MSL and was producing substantial engine power.