The first indication that a plane was down came Saturday afternoon when the Air Force Rescue Coordination Center at Tyndall Air Force Base in Florida picked up a signal from an emergency locator beacon transmitting from somewhere in the Anza-Borrego Desert State Park. The center alerted the California Wing of Civil Air Patrol. A search plane dispatched from Fallbrook found the wreckage in the mountains nine miles northeast of Borrego Valley Airport. But when a helicopter dispatched by the San Diego County Sheriff’s Department reached the crash site, there was no one to rescue. The pilot and any passengers on the mysterious flight were gone.