1922, Picardie, France
On April 7th 1922, two aircraft collided 110 Km north of Paris. It was the first collision between civil airliners. One was a French Farman Goliath, en-route from Paris Le Bourget to London Croydon. The other aircraft was a British DeHaviland DH-18 from London to Paris. Both were on the same route, but opposite, at 150m (500ft) in low visibility conditions. All seven passengers and crew on both aircraft died.
Following the accident, a meeting was called in Croydon. Here, experts established the first rules that would kickstart positive air traffic control. All aircraft were to fly and keep on the right side of defined routes. Aircraft were required to install radio equipment and keep in contact with ground stations. The meeting also clearly defined air routes between France, Belgium, the Netherlands and the UK.
De Havilland DH-18. 
The Farman F-60 Goliath involved in the collision