Five sheriff's deputies from Southern California and three National Guardsmen were killed when the helicopter they were flying in a joint drug interdiction mission snagged on a power line and exploded into a hillside in western Imperial County.

The accident occurred Monday, Oct. 24, about 9:30 p.m., approximately 63 miles east of San Diego on what was described as a training flight on the first night of an unpublicized anti-drug surveillance program called Operation Border Ranger. The National Guard UH-1H Huey helicopter crashed when it tried to make a pass through an isolated canyon to close in on a parked car thought to belong to drug smugglers, a National Guard spokesman stated.

Killed in the crash were five deputies from a consortium of six Southern California sheriff's departments that sponsored Operation Border Ranger, an anti-drug smuggling program that was quietly organized earlier this year. The three dead guardsmen were stationed with the 140th Aviation Unit at the Los Alamitos Armed Forces Reserve Center in Orange County.

The dead deputies were identified as Roy A. Chester, 41, of La Verne, and James D. McSweeney, 43, of Huntington Beach, both 12-year Los Angeles County Sheriff's veterans; Sgt. Richard G. Romero, 39, El Centro, a 14-year veteran in Imperial County; Mark Steven Tonkin, 31, Chino, a seven-year member of the Orange County Sheriff's Department; and Investigator Michael David Davis, 34, Indio, a nine-year veteran Riverside County deputy. San Diego and San Bernardino County Sheriff's Departments, the other participants in the program, had no one on board.

The deputies who died were all experienced narcotics officers.

Chester, who is survived by his wife, Marilyn, a 19-year-old daughter and twin 17-year-old sons, joined the narcotics detail in March 1984, and received numerous citations and commendations.