On 27 March 1977, a B747 aircraft belonging to KLM, collided with a B747 belonging to Pan Am while attempting to take off at Los Rodeos airport in Tenerife. Both aircraft had been diverted into Los Rodeos (Tenerife North) following an incident at Santa Cruz, Gran Canaria. Los Rodeos is at an altitude of 2000 ft and the visibility was reduced because of hill fog. The KLM aircraft began its take-off run having received en-route clearance but not take-off clearance and collided with the Pan Am aircraft which was taxi-ing down the runway. There were 583 fatalities. This is accident report was produced by ALPA Engineering and Air Safety.