In aviation, a mid-air collision is an accident in which two or more aircraft come into unplanned contact during flight.^[1] Owing to the relatively high velocities involved and the likelihood of subsequent impact with the ground or sea, very severe damage or the total destruction of at least one of the aircraft usually results.

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The potential for a mid-air collision is increased by miscommunication, mistrust, error in navigation, deviations from flight plans, lack of situational awareness, and the lack of collision-avoidance systems. Although a rare occurrence in general due to the vastness of open space available, collisions often happen near or at airports, where large volumes of aircraft are spaced more closely than in general flight.

Bobbie R. Allen, Director of Safety at the Civil Aeronautics Board said in a 1965 speech - "The threat of mid-air collision has existed ever since Orville turned to Wilber and said, 'Let's build another one.'"^{[citation needed]}

The first recorded collision between aircraft occurred at the "Milano Circuito Aereo Internazionale" meeting held between 24 September and 3 October 1910 in Milan, Italy. On 3 October, Frenchman René Thomas, flying the Antoinette IV monoplane, collided with British Army Captain Bertram Dickson by ramming his Farman III biplane in the rear.^[2] Both pilots survived, but Dickson was so badly injured that he never flew again.^[3][4][5]

The first fatal collision occurred over La Brayelle Airfield, Douai, France, on 19 June 1912. Captain Marcel Dubois and Lieutenant Albert Peignan, both of the French Army, crashed into one another in an early-morning haze, killing both pilots.^[6][7]

Almost all modern large aircraft are fitted with a traffic collision avoidance system (TCAS), which is designed to try to prevent mid-air collisions. The system, based on the signals from aircraft transponders, alerts pilots if a potential collision with another aircraft is imminent. Despite its limitations, it is believed to have greatly reduced mid-air collisions.^[8]

On some occasions, military aircraft conducting training flights inadvertently collide with civilian aircraft. The 1958 collision between United Airlines Flight 736 and a fighter jet, and another U.S. military/civilian crash one month later involving Capital Airlines Flight 300, hastened the signing of the Federal Aviation Act of 1958 into law. The act created the Federal Aviation Agency (later renamed the Federal Aviation Administration), and provided unified control of airspace for both civil and military flights. In 2005, in an effort to reduce such military/civilian mid-air collisions in U.S. airspace, the Air National Guard Flight Safety Division, led by Lt Col Edward Vaughan, used the disruptive solutions process to create a website called See and Avoid. It operated until January 2017.^[9]