What happened
The aircraft departed Tucson at 0559 local time and maintained routine communication with air traffic control, providing position reports over Casa Grande, Gila Bend, and Yuma, Arizona. At 0754, the American Airlines radio operator in San Diego transmitted a weather report indicating an indefinite ceiling of 1,200 feet with broken clouds and eight miles of visibility. Flight 6103 acknowledged this information and reported its position over El Centro, California, at 0753 while flying at 3,000 feet.
Los Angeles Airway Traffic Control subsequently issued a clearance for the flight to proceed to San Diego, instructing it to cruise at 8,000 feet and cross the destination at an altitude of at least 500 feet above the overcast. The company station attempted to relay this clearance to the aircraft at 0812. After several failed attempts to establish contact, Airway Traffic Control was informed that the clearance had not been delivered. All subsequent efforts to communicate with the flight were unsuccessful.
Search operations began immediately following the loss of contact. At 1305, personnel from the Naval Air Control Center in San Diego located the wreckage on the east slope of Thing Mountain, approximately ten miles southeast of Pine Valley. The impact forces destroyed the aircraft, and all 25 occupants were killed.
Findings
The investigation determined that the accident resulted from the pilot's action in descending into instrument conditions to an altitude below that required to maintain clearance over Thing Mountain. The specific reason for this descent was not determined.