The 1976 Zagreb mid-air collision took place on 10 September 1976, when British Airways Flight 476, a Hawker Siddeley Trident en route from London to Istanbul, collided mid-air with Inex-Adria Aviopromet Flight 550, a McDonnell Douglas DC-9 en route from Split, SFR Yugoslavia, to Cologne, West Germany, near Zagreb in modern-day Croatia. The collision was the result of a procedural error on the part of air traffic controllers in Zagreb.