Alaska Airlines Flight 1866 was a regularly scheduled passenger flight operated by Alaska Airlines from Anchorage, Alaska, to Seattle, Washington, with several intermediate stops in southeast Alaska. The aircraft was a Boeing 727-100 with U.S. registry N2969G manufactured in 1966. On September 4, 1971, the aircraft operating the flight crashed into a mountain in Haines Borough, about 18 miles west of Juneau, Alaska, while on approach for landing. All 111 people aboard were killed. The subsequent investigation found that erroneous navigation readouts led the crew to descend prematurely. No definitive cause for the misleading data was found. It was the first fatal jet aircraft crash involving Alaska Airlines, and remained the deadliest single-aircraft accident in United States history until June 24, 1975, when Eastern Air Lines Flight 66 crashed.