United Airlines Flight 266 was a scheduled passenger flight from Los Angeles International Airport, California, to General Mitchell International Airport, Milwaukee, Wisconsin, via Stapleton International Airport, Denver, Colorado. On January 18, 1969, at approximately 18:21 PST, the Boeing 727 operating the flight crashed into Santa Monica Bay, Pacific Ocean, about 11.5 miles (18.5 km) west of Los Angeles International Airport, four minutes after takeoff, killing all 38 on board.

Rescuers (at the time) speculated that an explosion occurred aboard the plane, a Boeing 727. Three and a half hours after the crash three bodies had been found in the ocean along with parts of fuselage and a United States mail bag carrying letters with that day's postmark. Hope was dim for survivors because the aircraft was configured for domestic flights and did not carry liferafts or lifejackets. A Coast Guard spokesman said it looked "very doubtful that there could be anybody alive."Up until 2013, United used "Flight 266" designation on its San Francisco–Chicago (O'Hare) route.