LOS ANGELES (AP) - Three people were killed Sunday in a pre-dawn helicopter crash in a rural area of northern Los Angeles County while filming for a new reality TV show for the Discovery Channel. The copter crashed at about 3:40 a.m. at the popular filming location of Polsa Rosa Ranch in the city of Acton, Los Angeles County Fire dispatcher Robert Diaz said. All three people aboard died, Diaz said. Their names weren't immediately released. The show, listed on a filming permit as an untitled military-theme TV program, had not yet been aired or announced by Discovery, channel spokeswoman Laurie Goldberg said. "A production company was shooting a show for Discovery Channel when this tragic accident occurred," the station said in a statement. We are all cooperating fully with authorities. Our thoughts and prayers go out to the families. The show's production company, Eyeworks USA, best known for creating NBC's "The Biggest Loser," also issued a statement expressing sympathies to the victim's families and saying they were cooperating with authorities. The company had been approved to use a helicopter for a reality TV show shooting at the ranch from Saturday afternoon until Sunday morning, said Philip Sokoloski, a spokesman for FilmLA, which processes filming permits for location shootings in the Los Angeles region. Records also showed Crossbow Helicopters received approval to participate in filming from the Federal Aviation Administration. The cause and other circumstances surrounding the crash are still unknown, Federal Aviation Administration spokesman Allen Kenitzer said. It was the site of another entertainment industry death in September, when a 48-year-old crew member died of an apparent heart attack while underwater in scuba gear on the set of the upcoming Johnny Depp film "The Lone Ranger" Sunday's wreck was also just 25 miles from a similar rural spot in Santa Clarita where actor Vic Morrow and two children were killed in another helicopter crash while filming the "Twilight Zone" movie in 1982. That crash brought changes in production restrictions and led to producer John Landis and four others being charged with involuntary manslaughter. All were acquitted. Associated Press writer Andrew Dalton in Los Angeles contributed to this report.