(January 2012) Sitting in the darkened area control center in Zurich, Switzerland, the air traffic controller on duty could scarcely believe what he was seeing on his radar screen: Somehow, two airliners in his sector cruising at precisely the same flight level were just miles apart on a collision course over southern Germany. Keying his microphone, the controller hurriedly commanded one of the aircraft, a Russian jetliner, to descend. The urgency in his voice conveyed the seriousness of the situation.
In the cockpit of the Tupolev Tu-154M passenger jet en route from Moscow to Barcelona, the pilots hesitated for a moment before initiating a descent from their assigned altitude of FL 360. Seconds later, the Russian jet’s TCAS issued a traffic resolution advisory commanding a rapid climb.
Faced with contradictory instructions, one from a human and the other from an onboard computer, the Russian crew chose to obey the controller’s original order.
Thus, the chain of events leading to one of Europe’s worst-ever air disasters was irrevocably set into motion.
Unbeknownst to the Russian pilots, a DHL Boeing 757 at that same moment was headed straight for them, the result of the controller in Zurich mistakenly allowing the converging jetliners to cruise at the same altitude. In the cockpit of the DHL jet, the crew also received a TCAS warning — in their case, commanding a descent. As both airplanes steadily began losing altitude, still on a deadly collision course, the controller never intervened. Seconds ticked past on the dark night until the DHL jet, traveling at more than 500 miles per hour, sliced into the Tupolev at a nearly perfect right angle and an altitude of 34,980 feet, splitting the Russian airplane in two. The Tu-154 broke into large sections, fore and aft, the twisted metal raining down over a remote German town near the Swiss border. All on board were killed, including 57 passengers, most of them Russian schoolchildren headed to Spain for summer vacation. The badly damaged 757 managed to stay aloft for another four miles before crashing and killing its two pilots.
How could this midair collision — occurring at 10:36 p.m. local time on July 1, 2002 — possibly have been allowed to happen? In this era of advanced traffic alert and collision avoidance systems and ground-based surveillance radar, and with professional pilots and a controller on hand to continually manage aircraft trajectory, altitude and speed, how did it come to pass that two massive jetliners weighing nearly a half-million pounds combined would occupy the same point in the sky at precisely the same instant even as those safety devices and the controller on duty issued a multitude of warnings?
As is the case in most such tragedies, it was a series of unfortunate events that doomed the lives of 71 passengers and crew — and, it would turn out, also claimed the life of the Zurich controller when, two years later, the Russian father of two of the young victims murdered him in a revenge killing outside his Zurich home. Had any one of the links in the accident chain been broken, all involved might still be alive today.