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The terrible moments at Tenerife served as a reminder that modern man, such an assumed master of technology, will never be able to control perfectly the wondrous machines he creates. Seventy investigators—representing Spain, which holds sovereignty over the Canary Islands, the U.S., The Netherlands, Pan Am and KLM—probed the disaster. Human error seemed the most probable cause. As U.S. Federal Aviation Administrator John McLucas put it: "Apparently not everybody had his head up." The only other possibility was an unlikely malfunction in radio equipment that could have prevented the KLM pilot from hearing the last vital communications from the airport tower or from the Pan Am cockpit. If both pilots and the tower controllers had fully heard —and understood—one another, the KLM pilot would never have sent his craft hurtling toward takeoff before the Pan Am plane was off the runway.
The basic causes of the disaster will probably be known when investigators finish analyzing the contents of four remarkable "black boxes" recovered from the wreckage of the two planes and sent to Washington, where there are sophisticated laboratory facilities. Actually luminous orange, the devices record all conversations in the cockpits of the two planes and critical precrash mechanical factors. Though a full report may be months in the making, the search for a cause has already narrowed to a few key mysteries:
> Why had KLM Pilot Jacob Veldhuizen Van Zanten, 51, a 25-year career flyer so experienced that he spent half his time training other KLM pilots (when a KLM official first heard of the crash he wanted to send a pilot to the investigation: Veldhuizen), rolled toward takeoff without getting tower clearance to do so? Even defensive Dutch authorities agreed that "no takeoff clearance had been given."
> Had Pan Am Pilot Victor Grubbs, 56, who had 32 years experience, actually been directed by the tower to take an awkward, 135° backward exit onto Tenerife's ramp C-3 rather than use the more gently angled ramp C4? Grubbs was heading toward C-4 as he moved to get in position behind the KLM plane to make his own takeoff. If he had made the earlier turn, he might have been clear of the runway before the KLM 747 reached that exit point.
> Why had the KLM pilot not heard the Pan Am Clipper's report that it had not yet cleared the runway and would report again when it had? Or had the KLM crew somehow mistaken the Pan Am message to mean that the Clipper had, rather than had not, cleared the runway? Even if there had been such a misunderstanding, of course, the KLM pilot should have awaited the tower O.K. to proceed.