Iberia flight IB350, a Boeing 727, and Aviaco flight 134, a DC-9-30, collided on the runway at Madrid-Barajas Airport in heavy fog, killing 93. Aviaco DC-9 EC-CGS taxied out for takeoff in heavy fog (approx. 300 m visibility) for a flight to Santander. The aircraft inadvertently taxied onto the active runway 01. At that exact same moment an Iberia Boeing 727 (EC-CFJ) was taking off and was at or near the V1 speed when the crew noticed the DC-9 in front of them. They unsuccessfully tried to take evasive action; The 727’s left wing and left main gear were torn off in the collision. Both aircraft caught fire and burned out. PROBABLE CAUSE: “The unknown incursion of DC-9 on the runway 01/19, when the B727 was on take-off roll. The DC-9 was on the active runway because visibility conditions due to fog by the zone where the aircraft was taxiing, impeded to the crew obtain sufficient visual references to determine that that was not the correct run that they should realize to reach the threshold of runway 01.”