North Park is a neighbourhood of small houses and jacaranda streets, a few miles short of the runway at Lindbergh Field. The crew coming in over it that morning in 1978 were Captain James McFeron, First Officer Robert Fox and Flight Engineer Martin Wahne, flying the ordinary shuttle work PSA did all day — up from Sacramento, down through Los Angeles, San Diego by mid-morning. A short hop, the last leg, the descent already begun. The Cessna was out doing instrument practice in the same patch of sky.
Everyone aboard both aircraft was killed, and seven people on the ground, at home on a Monday. It was the first fatal accident in the airline's history. I won't put any of it in numbers beyond that.
One thing that came out of it: the push for airborne collision avoidance moved from research to requirement. TCAS, the box that talks to other aircraft's transponders and tells the crew to climb or descend, was mandated for US airliners by Congress in 1987 and phased in through the early nineties.
An aircraft converging on a collision course sits still in your field of view — no relative movement, so nothing draws the eye to it. Against roofs and streets below, a small plane is a few minutes of arc, and the eye needs motion or contrast to find something that size. It is a real limit of human vision, not of attention.