MASON CITY, Iowa (AP) — Three people are dead after a medical helicopter flying out of Mason City, Iowa, crashed into a field, authorities say. Cerro Gordo County Sheriff’s Department Lt. Matt Klunder said the helicopter was affiliated with Mercy Medical Center and that a pilot and two nurses were killed. Klunder said the crash occurred about 9 p.m. Wednesday near Ventura, Iowa. The identities of the victims were not released, and the cause of the crash was under investigation.