Hughes Airwest Flight 706 was a regularly scheduled flight operated by American domestic airline Hughes Airwest from Los Angeles, California to Seattle, Washington, with several intermediate stops. On Sunday, June 6, 1971, the McDonnell Douglas DC-9 serving as Flight 706 departed Los Angeles just after 6 p.m. en route to Seattle as a McDonnell Douglas F-4 Phantom II of the United States Marine Corps was approaching Marine Corps Air Station El Toro near Irvine at the end of a flight from Naval Air Station Fallon in Nevada. The two aircraft collided in midair over the San Gabriel Mountains near Duarte, killing all 49 aboard the DC-9 and the F-4 pilot; the F-4 radar intercept officer ejected and survived.

Hughes Air Corporation, doing business as Hughes Airwest, was a local service carrier from 1970 to 1980 in Western United States. It was backed by Howard Hughes' Summa Corporation. Its original name in 1968 was Air West and the air carrier was owned by Nick Bez. Hughes Airwest flew routes in the western U.S. and to several destinations in Mexico and Canada; its headquarters were on the grounds of San Francisco International Airport (SFO) in unincorporated San Mateo County, California.