The DC-7B had taken off from Santa Monica Airport at 10:15 a.m. on its first functional test flight, earmarked for delivery to Continental Airlines. The F-89J had taken off from Palmdale at 10:50 a.m. on a radar test flight. Both aircraft were performing tests at 25,000 feet over the San Fernando Valley under visual flight rules—meaning their crews were responsible for seeing and avoiding other aircraft. Investigators later concluded they most likely converged northeast of the Hansen Dam spillway. The collision was near-head-on and at high speed. The F-89J's radarman, Curtiss Adams, managed to bail out and parachuted to a garage roof in Burbank, suffering severe burns and a broken leg. The fighter's pilot, Roland E. Owen, died when the aircraft fell in flames into La Tuna Canyon. Eight people died in total. Seventy-four were injured.

The wreckage that fell into the Pacoima Junior High School playground came down among students who had no warning. The casualties—eight dead, dozens injured—were a shocking demonstration of what could happen when uncoordinated test flights shared the same airspace above populated areas. The Civil Aeronautics Board, which investigated the crash, attributed it to pilot error and the failure to properly exercise "see and avoid" procedures. In response, the CAB required that all aircraft test flights, military and civilian, be conducted over open water or specifically approved sparsely populated areas. The rule changed how test aviation worked in America.

Richard Steven Valenzuela, who would become famous as Ritchie Valens, was a 15-year-old student at Pacoima Junior High—but he was not there that morning. He was absent, attending the funeral of his grandfather. His classmates and friends were in that schoolyard. The crash haunted him nonetheless. Recurring nightmares led to a persistent fear of flying—a fear he eventually overcame as his music career took off. He overcame it, and then, on February 3, 1959, he died in a plane crash near Mason City, Iowa, along with Buddy Holly, the Big Bopper, and pilot Roger Peterson. The connection haunted the people who knew him: the boy who had been spared by a funeral, who was afraid of flying, who flew anyway, who died flying. Two years, two crashes. One life.

The 1957 Pacoima collision was discussed nationally—the New York Times ran the story, CBS Radio Workshop devoted an episode to it in May 1957. But over time it faded from general awareness, overshadowed by Valens's death in 1959 and the larger myth of "the day the music died." Joan Gushin, who has devoted significant effort to documenting the crash and its survivors, maintains a website that includes interviews, injury lists, and archival photographs. The crash remains, for those who know it, one of those events that altered the rules—both the formal rules of airspace management and the more personal rules that people carry about risk and fate and the sky.