There were no markings or signs to identify the runway exits. (Coincidence number six) This was a crucial omission on the part of the airport authorities as these exist are marked clearly all over the world and certainly were at that time. The Pan Am crew appeared to remain unsure of their position on the runway until the collision, which occurred near the intersection of the fourth taxiway (C-4). Pan Am's lack of visibility and runway exiting confusion contributed to a slow taxi speed, thereby causing the aircraft to remain on the runway longer than anticipated. (coincidence number seven)
The angle of the third taxiway would have required the plane to perform a turn of approximately 145°, which would lead counter-productively back toward the still-crowded main apron. At the end of C-3 another 145° turn would have to be made to continue taxiing towards the start of the active runway. (see diagram above)
Taxiway C-4 would have required two turns of just 35°. A study carried out by the Air Line Pilots Association after the accident concluded that making the second 145° turn at the end of taxiway C-3 would have been "a practical impossibility", although the Dutch report stated that such a maneuver "could reasonably be performed". The official report from the Spanish authorities did not explain why the controller had instructed the Pan Am aircraft to use the third taxiway, rather than the sensible and easier fourth taxiway.
Immediately after lining up, the KLM captain advanced the throttles (a standard procedure known as "spool-up", to verify that the engines are operating properly for takeoff) and the co-pilot, surprised by the maneuver, quickly advised the captain that ATC clearance had not yet been given. Captain Van Zanten responded, "I know that. Go ahead, ask." Meurs, the FO, then radioed the tower that they were "ready for takeoff" and "waiting for clearance". The KLM crew then received instructions which specified the route that the aircraft was to follow after takeoff. (the departure clearance) The instructions from the controller used the word "takeoff," but did not include an explicit statement that they were cleared for takeoff.
Meurs read the flight clearance back to the controller, completing the read-back with the statement: "We are now at takeoff." Captain Van Zanten interrupted the co-pilot's read-back with the comment, "We're going." As noted in the NOVA documentary of the incident, the co-pilot sadly chose not to contradict or embarrass his superior a second time by stating that they still did not have the proper clearance to take off. Tragic error… (coincidence eight and the close to the final one of the series) When in doubt speak the hell up! In a cockpit environment, too often the FO (co-pilot) is too damm timid. The old-time captains often contributed to this by acting like pompous idiots , further intimating the co-pilot.
The controller, who could not see the runway due to the fog, initially responded with "OK" (terminology which is nonstandard), which reinforced the KLM captain's misinterpretation that they had takeoff clearance.
The controller's response of "OK" to the co-pilot's nonstandard statement that they were "now at takeoff" was likely due to his misinterpretation that they were in takeoff position and ready to begin the roll when takeoff clearance was received, but not actually in the process of taking off.
The controller then immediately added "stand by for takeoff, I will call you," indicating that he had not intended the clearance to be interpreted as a takeoff clearance. He probably had not heard the captain's announcement that they were "going," since Van Zanten had said this to his fellow crew members and not transmitted it on the radio himself.
A simultaneous radio call from the Pan Am crew caused mutual interference on the radio frequency, which was audible in the KLM cockpit as a three second long whistling sound (or heterodyne). This made the crucial latter portion of the tower's response audible only with difficulty by the KLM crew. The Pan Am crew's transmission, which was also critical, was reporting, "We're still taxiing down the runway, the Clipper 1736!" This message was also blocked by the heterodyne and inaudible to the KLM crew. Either message, if heard in the KLM cockpit, would have given the KLM crew time to abort its second takeoff attempt. What blocked these crucial transmissions? Whatever it was it was in this , the final coincidence, number nine!
Due to the fog, neither crew was able to see the other plane on the runway ahead of them. In addition, neither of the aircraft could be seen from the control tower, and the airport was not equipped with ground radar.
After the KLM plane had started its takeoff roll, the tower instructed the Pan Am crew to "report when runway clear." The Pan Am crew replied: "OK, we'll report when we're clear." On hearing this, the KLM flight engineer expressed his concern about the Pan Am not being clear of the runway by asking the pilots in his own cockpit, "Is he not clear, that Pan American?" Van Zanten emphatically replied "Oh, yes" and continued with the takeoff, accelerating into eternity and into the hands of death, the hunter…….
KLM Captain Van Zanten, already traveling too fast to stop, also attempted to avoid a collision by prematurely rotating his aircraft and attempting to climb, scraping the tail of the plane along the runway for 20 m (66 ft). As the KLM left the ground, its steep angle of attack allowed the nose gear to clear the Pan Am but the engines, lower fuselage and aft landing gear struck the upper right side of Pan Am's cabin at approximately 140 knots (260 km/h; 160 mph), ripping apart the center of the Pan Am jet almost directly above the wing. The right side engines crashed through the Pan Am's upper deck immediately behind the cockpit.
The KLM plane was briefly airborne, but the impact with Pan Am sheared off the #1 (outer left) engine, and the #2 (inner left) engine had ingested significant amounts of shredded materials from Pan Am’s aircraft. Van Zanten lost control, and his 747 went into a stall, rolling sharply, impacting the ground 150 m (500 ft) past the collision, sliding a further 300 m down the runway. The full load of fuel which had caused the earlier delay ignited immediately. The KLM crew saw what happened, they were alive and conscious as their tortured and disintegrating aircraft hurled toward their doom.
A survivor of the Pan Am flight, John Coombs of Hawaii, said that sitting in the nose of the plane probably saved his life: "We all settled back, and the next thing an explosion took place and the whole side of the plane, was just torn wide open."
The other 56 passengers and 5 crew members aboard the Pan Am aircraft survived, including the pilots and flight engineer. Most of the survivors on the Pan Am aircraft walked out onto the left wing, the side away from the collision, through holes in the fuselage structure. Pan Am’s engines were still running at takeoff power for a few minutes after the accident despite First Officer Bragg's attempt to shut them down..
The cockpit overhead, where the engine emergency shut down switches were located, had been destroyed in the collision- all control lines were severed, leaving no way for the flight crew to control them. After a short time running at full power the engines began to disintegrate, throwing engine parts at high speed, killing one of the flight attendants who had escaped the burning plane.
Survivors waited for rescue but it did not come promptly as the firefighters were initially unaware that there were two aircraft involved and were concentrating on the KLM wreck some distance away in the thick fog. Eventually, most of the survivors on the Pan Am aircraft wings jumped to the ground some 10’ below. ( photo above)
Captain Veldhuyzen van Zanten was KLM's chief of flight training and the airline's preferred pilot for publicity