On this day in 1977, two Boeing 747s collided on a fog-covered runway at Tenerife Airport (formerly Los Rodeos) in Spain. It is one of the worst plane crashes ever, killing 583 people.

It all started with an explosion at Gran Canaria airport in Spain. Due to this event, several flights were diverted to Tenerife Airport, including KLM (flight 4805) and Pan Am (flight 1736).

As a result of dense fog, lack of radar, poor communication between the tower and the plane, possibly pilot error, the two Boeing 747s collided on the runway. Everyone died on the KLM plane, and 61 people survived on the Pan Am plane.

On that day, a militant separatist group planted a small bomb at Gran Canaria's Las Palmas airport, which closed the airport and diverted air traffic to the much smaller Los Rodeos airport in Tenerife.

As the runway at Los Rodeos was full of planes, overwhelmed controllers began diverting flights. Both Boeings, Pan Am 1736 bound for Los Angeles and KLM 4805 were sent to the road that served as a taxi stand next to the runway.

KLM pilot Jacob Veldhuizen van Zanten took the opportunity to refuel his plane, which took about 35 minutes. As soon as the charging was complete, he started the engines. Pan Am was run by Paul Grubbs.

Van Zanten was an experienced pilot who had previously trained young service pilots and flew less frequently. He spent most of his time on simulators. As the foreign media write, he was so popular and photogenic that the company used him as a spokesperson in its marketing materials.

Both pilots were eager to get going, Wired reports, especially Grubbs who had already been flying for eight hours and was tired.

In an attempt to move Pan Am 1736 off the main runway, controllers ordered Grubbs to divert to Runway 3. The weather was deteriorating, Grubbs was unfamiliar with the airport and had trouble locating the correct runway in the reduced visibility.

Van Zanten, in KLM 4805, was preparing for take-off. He knew that the Pan Am plane was parked nearby, but he did not know that it had also left. He asked for permission to take off and was told it could be ready soon.

It is not known whether he misheard the instruction or ignored the message, but Van Zanten continued the takeoff.

What he didn't know was that Pan Am 1736 was heading down the runway directly toward him, still looking for a designated taxiway.

As later revealed in cockpit footage, Pan Am's first man, Robert Bragg, spotted the KLM plane's lights through the fog and yelled at Grubbs, who tried to steer the Pan Am plane off the runway. But it was too late.

KLM 4805 hit Pan Am at full throttle. Due to the force of the impact, it flew 30 meters into the air, crashed on the runway and exploded.

Pan Am 1736 also caught fire, disintegrating into several pieces. Most of the survivors of that plane were seated in front of the right wing.

All 248 people in KLM 4805 died. Pan Am 1736 killed 335 people, and seven of the flight's 16 crew members, along with two company employees and 61 passengers, survived. Nine passengers later died from their injuries.

Pilot Grubbs was not among the survivors.

Despite the various factors that led to the disaster, the official investigation placed all the blame on Van Zanten. The veteran pilot's biggest sin, caused by impatience or poor communication, was taking off without permission from the tower.

If Van Zanten had waited, the accident would never have happened, the American media write.