The Grand Canyon mid-air collision occurred in the western United States on June 30, 1956, when a United Airlines Douglas DC-7 struck a Trans World Airlines Lockheed L-1049 Super Constellation over Grand Canyon National Park, Arizona. The first one fell into a canyon and the other one slammed into a rock face. All 128 on board both airplanes perished, making it the first commercial airline incident to exceed one hundred fatalities. The airplanes had departed Los Angeles International Airport minutes apart from each other and headed for Chicago and Kansas City, respectively. The collision took place in uncontrolled airspace, where it was the pilots' responsibility to maintain separation. This highlighted the antiquated state of air traffic control, which became the focus of major aviation reforms.

United Airlines, Inc. is a major American airline headquartered at the Willis Tower in Chicago, Illinois. United operates an extensive domestic and international route network across the United States and all six inhabited continents primarily out of its eight hubs, with Chicago–O'Hare having the largest number of daily flights and Denver carrying the most passengers in 2023. Regional service is operated by independent carriers under the brand name United Express.