Because of radio interference, a KLM Royal Dutch Airlines crew never heard vital control tower instructions that might have prevented the Canary Island airport runway collision of two jumbo jets that killed 577 people last month, informed sources said yesterday.
A preliminary study by U.S. investigators of the tape recordings from the KLM jetliner's cockpit also appears to confirm that the Dutch crew started the takeoff without receiving formal permission from air traffic control.
The result was that the KLM Boeing 747 jet collided with a Pan American World Airways 747 on the runway at Los Rodeos Airport on Tenerife Island in the Canaries. Only 67 people survived the fiery March 27 crash, which was the worst disaster in aviation history.
Since the early days of the investigation, it has been known that the air traffic control tape contained no formal takeoff clearance for the KLM jet. Dutch officials said so. They also said that the Pan Am jet missed a turnoff that would have carried it safely off the runway before the KLM plane started.
Since that time, the investigation by Spanish, U.S. and Dutch civil aviation authorities has centered on what was heard in the cockpits of the two air-planes.
According to a transcript of the tower radio traffic made available by the Spanish, this important exchange took place seconds before the accident:
KLM to tower - "KLM is now ready for takeoff and we're waiting for our ATC (air traffic control) clearance."
The tower then gave the KLM crew navigational instructions to be followed after takeoff.
KLM to tower - "We are not on (or at) takeoff."
Tower to KLM - "OK, Standby for takeoff. I will call you."
According to sources familiar with the investigation, the tape recording of what was said and heard in the KLM cockpit shows that the words "Standby for takeoff, I will call you," were never heard by the KLM crew.
The KLM crew apparently heard only "OK" and started to roll.
The rest of that crucial message from the tower was blocked, experts theorized, by another transmission from a third source - possibly even the Pan Am plane.
It will be days and probably weeks before the investigative team that is painstakingly working on the mystery is able to come up with a definitive transcript. That transcript would include all possible sources of radio traffic - the two planes, the tower, and others who might have shared that common frequency.
A mystery remains about why the KLM crew would begin the take off roll on "OK." Tha is not a standard clearance. Normally, air traffic control experts said, the roll for takeoff would begin only after the controller had said: "KLM 4805, cleared for takeoff."
KLM officials have insisted that it was "inconceivable" their crew would begin without such a clearance.
The investigation is far from complete and some new revelation is always possible. But it is already known that a number of events preceding the accident combined to makeither of the planes should have been at Tenerife in the ither of the planes should have been at Tenerif in the fifirst place. They were diverted there from nearby Las Palmas airport, on the Grand Canary Island, when a terrorist bombing closed the larger, a more adequate airport there.
A Spanish investigator approached an American reporter in the Tenerife Airport the week after the accident, grabbed him by the sleeve and said with passion, "Blame this on the terrorist. That's the first fault."
The KLM flight, loaded with 234 Dutch, German and Austrian tourists and a crew of 14, had left Amsterdam at 9:20 a.m. that Sunday morning and had landed at Tenerife at 1:40 p.m. The small, one-runway airport was already full of jets headed for their original destination Las Palmas, and the KLM plane had to park just off the runway at its northwest end. Time passed.
More planes came in, including the Pan Am flight, carrying a total 396 people, most of them tourists from the Los Angeles areas.
The Pan Am plane was forced to park on the taxi strip that parallels the runway, some distance south of the KLM jet. More time passed.
The fog began to roll in. Tenerife Island goes from the ocean straight up. Santa Cruz, the main city, is at sea level, the airport is 20 minutes uphill by taxi, at 2,000 feet. When the low Atlantic clouds roll in and out, they obscure the runway and the neatly terraced farms beyond it.
Finally, the word came that Las Palmas was open again. The taxi strip was full of planes, so the runway had to be used as a taxiway. The KLM captain, 25-year-veteran Jacob Veldhuizen Van Zanten, elected to take on fuel so he would'nt have to do that at Las Palmas for the return trip to Holland.
Two smaller jets were able to get around the refueling KLM plane, taxi to the south end of the runway and take off. The Pan Am jet could not; there was not enough clearance between KLM and the side of the runway, so the Pan Am crew sat and waited as did the KLM crew and the passengers in both planes.
Finally, around 5 p.m., KLM started taxing down the runway and the Pan Am followed. The fog was intense. It is clear from the evidence available that nobody could see anybody else.
"How many taxiways have you passed?" the tower asked KLM at one point. "I think we passed C4 now," the KLM crew responded.
According to Robert Bragg, the Pan Am co-pilot who held a press conference this week, he and Capt.Victor Grubbs decided as they were taxing down the runway behind the KLM that they couldn't take off once they got to end of the runway because visibility was so bad.
That decision was forced when the tower told both planes that the runway centerline lights were out. Centerline lights illuminate the middle of the runway and help a pilot keep things straight while rolling. According to Pan Am regulations, visibility would have to 800 meters - about half a mile - or better with no centerline lights for Pan Am planes take off. A somewhat lower visibility - not yet determined - was permitted by KLM regulations.
Pan Am's crew also discussed the meaning of the tower's instruction to take thirrd runway exit on the left for the taxiway. According to Bragg, the Pan Am charts showed that exit C-1 (see chart) was closed. Therefore, exit C-4 would be the third left exit, Pan Am asked the tower to confirm that it was to turn left at the third intersection.
The tower replied: "Yes, third one, two, three, third one." Exit C-3 made no sense to the Pan Am crew because it was an impossibly sharp turn for a big 747. It was agreed that C-4 was the third exit. Bragg said, and Pan Am officials have so insisted.
Pan Am was crawling along the runway in the fog . The KLM reached the end of the runway and turned around, a slow process with the huge jet. The fog, the long day, a planeload of at least partly disgruntled passengers, and the tower says. "OK."
After the tower broadcast the "standby" instruction that KLM apparently never heard it asked Pan Am to report when the runway was clear. The last Pan Am transmission was "Roger, we'll report which we're clear."
Bragg said Pan Am was taxiing at about 10 m.p.h. looking for taxiway headlights. "We thought the KLM was still parked. Then we saw the lights moving, then we saw the plane Bragg estimated visibility at about 500 meters - something more than a quarter-mile - as the KLM plane came into view.
Pilot Grubbs shouted "Get off. Get Off," then jammed the throttles full ahead and tried to get his plane off the runway.
The KLM pilot had the same kind of terrifying realization apparently - just an instant's warning. He tried to get his plane airborne several hundred feet before it would be ready to lift off. He pulled the nose up so high that the tail dug a 22-meter long trench - 72 feet - in the runway.
After the collison and the fire and the explosions, one of the Pan AM engines continued to run on the ground, spewing its internal works like shrapnel across what witnesses later descirbed as a battlefield-like scene.
If the investigation proves that "OK" used by the tower taken as a takeoff clearance by the KLM crew, the tougher question of why will have to be addressed theoretically. No one on the KLM plane survived.
"Sometimes you think you hear what you want to hear," a Pan Am pilot said in an interview. "I started once, and the tower stopped me."
Gary Babcock, a human performance specialist for the Air Line Pilots Association, stressed that he was not familiar with the specifics of the KLM incident or crew history. "But there are some pretty well accepted things about being tired," he said. "We know that fatigue results in lenghtened reaction time and less ability to process information."
By the end of today, about half of the 326 bodies taken from the Paan Am wreckage will have been identified by specialists working at Dover Air Force base and the remains returnedto the next of kin, Pan Am spokesmen said yesterday.