Note: this accident was previously featured in episode 18 of the plane crash series on January 6th, 2018, prior to the series’ arrival on Medium. This article is written without reference to and supersedes the original.
It is perhaps one of the saddest stories in the history of commercial aviation: a plane full of a Russian republic’s brightest young students — her aspiring artists, musicians, and athletes — ripped so cruelly from the sky, their hopes and dreams scattered across the fields of southern Germany. It is a story of split-second decisions, made amid a fog of confusion in the dead of night, which sent two airliners careening into one another at 35,000 feet. It is a story of a tragedy which could have been avoided, and of a man in the throes of grief who sought his own perverted justice in the murder of the air traffic controller he deemed responsible.
The tragic tale of the Überlingen disaster and its aftermath comes across like a modern-day Shakespearean drama. But the crash was also about a fundamental blind spot in the global air traffic control system, a gap whose existence authorities had failed to close. And it was perhaps a distant echo of the collapse of the USSR, a reminder that the Russian and Western aviation industries still possessed divergent impulses, whose untimely intersection could plant the seeds of disaster. Now, twenty years after the accident, long after the closure of its final chapters, we can look back upon the events of the 1st of July 2002 from both perspectives — literary and scientific — to tell the story of a profound human tragedy and the deficient system which made it inevitable.
Far to the east of Moscow, in the rolling hills along the margin of the Ural Mountains, lies the city of Ufa, capital of the autonomous Republic of Bashkortostan. Like most of the Russian interior, it fell on hard times during the 1990s, as the collapse of the Soviet Union devastated the local manufacturing industry and plunged thousands into poverty. Even by 2002, as Russia’s economy started to turn around, travel opportunities for the people of Ufa were limited.
It was therefore quite a cause for celebration when the city’s special UNESCO-affiliated school announced that its parent agency, the United Nations Educational, Scientific, and Cultural Organization, would organize a field trip to a planned UNESCO youth festival on Spain’s prestigious Costa Dorada. A few dozen of the school’s top students were selected, some for their academic prowess, others for their skill in art, music, athletics, and other fields. Others bought their way in: the parents of some schoolchildren paid several hundred dollars apiece to send their children on the trip, a substantial sum of money which some could only afford at the expense of their own planned vacations.
The school group, including some 44 children between the ages of 8 and 18, traveled to Moscow on June 29th, 2002, where they planned to catch a commercial flight to Barcelona. But their bus driver accidentally took them to the wrong airport — Moscow has several — and they missed the flight.
While most travelers could simply go to the check-in counter and arrange to board a later flight, the group of 44 kids and five adult chaperones would need special accommodation. Stuck in Moscow while the trip organizers frantically searched for a transportation solution, the children toured the Red Square, the Kremlin, and other national landmarks, snapping photos of each other’s smiling faces in front of the high, red walls. They could not have known that their unexpected layover in the capital would be the first link in a deadly chain of events that would shock the world.
After two days in Moscow, the school group received a lucky break: a local airline, having heard of the plight of the kids from Ufa, was able to arrange a charter flight to Barcelona on the night of July 1st. The company in question was Bashkirian Airlines, the de facto flag carrier of the Republic of Bashkortostan, which had split off from a regional Aeroflot subsidiary in 1992 and now carried passengers throughout central Russia and to popular holiday destinations abroad, including Barcelona. Between its local connections and its experience with the destination airport, it was ideally positioned to carry out the flight on short notice. And so, late on the night of the 1st of July, the kids and their chaperones boarded a Bashkirian Airlines Tupolev Tu-154 at Moscow’s Domodedovo International Airport.
They were joined by eight passengers who were not part of the school group, but had also missed earlier flights to Barcelona. A family of four from Belarus is thought to have been among them. Also on board were Svetlana Kaloyeva and her two children, Konstantin, 10, and Diana, 4, who were on their way to visit their father Vitaly Kaloyev, an architect from the North Caucasus town of Vladikavkaz who was working in Barcelona that summer on a vacation home for a Russian oligarch. Added onto the school group, the five other unaffiliated passengers, and the twelve crewmembers, the Kaloyev family brought the total number of people on board to 69.
Although their three-engine Tupolev Tu-154 was designed in the 1960s in the Soviet Union, this particular example was much newer, having been produced in Russia in 1995, and was equipped with some of the latest technology. Nevertheless, a large cockpit crew was required to fly it. That night, there would be no less than five pilots aboard, including 52-year-old Captain Aleksandr Gross; 41-year-old Instructor Captain Oleg Grigoriev, the chief pilot at Bashkirian Airlines, who was overseeing Gross as he familiarized himself with the procedures at Barcelona; 50-year-old Navigator Sergei Kharlov; 37-year-old Flight Engineer Oleg Valeev; and 41-year-old First Officer Murat Itkulov. However, Instructor Captain Grigoriev was sitting in the right seat performing the duties of pilot not flying, so First Officer Itkulov simply rode along in the jump seat without being assigned any specific duties. Also on board were four flight attendants and three other Bashkirian Airlines employees riding behind as passengers, totaling twelve crewmembers.
All seemed routine as the Bashkirian Tu-154, operating under the flight number BTC 2937, departed Moscow and headed west across Europe, cruising at 36,000 feet. One air traffic control sector gave way to another, and by 23:30 Central European time they were over southern Germany, passing overhead Munich. At that time, anticipating its imminent entrance into neighboring airspace controlled from Zürich, Switzerland, the Munich area controller handed the flight over to his Zürich-based counterpart.
That night, a single controller was handling all the airspace within the Zürich air traffic control sector. The facility handled all mid- and high-level traffic in an area covering northeastern Switzerland and southwestern Germany, as well as approach services for aircraft descending into airports in St. Gallen and Friedrichshafen. Tonight, all of these duties fell on the shoulders of just one man: Danish-born air traffic controller Peter Nielsen. Normally, this would not be a particularly stressful arrangement. Traffic in the region at this hour was usually light, since all the nearby major airports had closed for the night, leaving only high-level transiting aircraft bound for other parts of Europe. At the facility, it had become common practice for one of the two controllers on duty to take an extended rest in the break room during the middle of the night shift once the last planes had landed in St. Gallen and Friedrichshafen, and tonight was no exception. The other qualified controller left the control room at 23:15, and their assistant left ten minutes later, leaving only Nielsen and another assistant who was not authorized to control aircraft.
For Nielsen, this wasn’t an unusual situation, and he anticipated no difficulties controlling the two or three aircraft that were typically in his airspace at this time of night. But on the night of July 1st, there were additional complications. The air traffic control company had recently decided to make modifications to the way it divided the upper level airspace, necessitating several changes to the computer hardware that kept the control center running. Part way through Nielsen’s shift, a group of technicians arrived to install the update, and he was informed that his work station’s main computer would have to be shut down, causing his displays to operate in fallback mode — a secondary condition in which several features provided by the main computer became unavailable. In fallback mode, the system which automatically correlated an aircraft’s radar return with its filed flight plan would not work, forcing him to enter the information manually, and the Short-Term Conflict Alert light, which illuminates when the system predicts that two planes will pass too close, would be rendered inoperative. But Nielsen had no idea what features would be lost in fallback mode, nor did he have any obvious way of finding out. And as if that wasn’t enough, a few minutes later the technicians informed him that they would also have to disconnect the control center’s direct telephone landline to neighboring centers. The glitches were adding up, but with so few planes in the air, how dangerous could it be?
But, just moments after the Tu-154 entered Zürich airspace, Nielsen faced another complication: an Airbus A320 belonging to German charter airline Aero Lloyd contacted Zürich, reporting that their flight had been delayed and they wanted to perform a late approach to Friedrichshafen Airport. When the second controller went off duty, no one had anticipated that an aircraft would try to land at Friedrichshafen after its nominal closing time, so Nielsen was forced to abruptly switch his focus to the approach sector, which normally wouldn’t have been his responsibility. It would have been possible to call and wake the second controller, who normally handled approach services, but for just one plane, it didn’t seem worth it. After all, with the Aero Lloyd plane already lined up for approach, all Nielsen needed to do was tell Friedrichshafen that it was coming. He picked up the direct landline to the Friedrichshafen control tower, but it had been disconnected. He tried using the regular phone system to call a posted phone number for the tower, but that didn’t work either. This was starting to become more complicated than he had anticipated.
Meanwhile on board the Tu-154, the pilots spotted another plane in the distance, appearing on the situational display of their Traffic Collision Avoidance System. The system, or TCAS (tee-cas), incorporates altitude, speed, and heading information broadcast by the transponders of nearby aircraft, compares it to the aircraft’s own trajectory, and automatically assesses the relative threat of a collision. If the planes’ projected paths come too close, both airplanes’ collision avoidance systems will simultaneously issue opposite “resolution advisories,” telling one plane to climb and the other to descend. But so far, this other plane was still more than 10 nautical miles away, too distant for the system to suggest such drastic action.
Despite the distance, however, Instructor Captain Grigoriev could already see the plane’s flashing anti-collision lights blinking against the blackness of the moonless night. “Here, visually,” he said, pointing out the window. “[And] here it’s showing us zero,” he added, referring to the TCAS display, where the number representing the height difference between his aircraft and the intruder indicated zero feet.
This other plane was in fact DHL flight 611, a Boeing 757 cargo plane hauling packages from Bergamo, Italy to Brussels, Belgium. The flight had departed earlier that day from Bahrain, where DHL has its own local subsidiary airline, and was now on the second leg of its trip after a scheduled cargo swap in Bergamo. In command were two experienced pilots: 47-year-old Captain Paul Phillips, and 34-year-old First Officer Brant Campioni. Although they lived in Bahrain, they were originally from the UK and Canada, respectively. No one else was on board.
Phillips and Campioni had made contact with Nielsen at 23:21 and were cleared five minutes later to climb to 36,000 feet in accordance with their flight plan. Unbeknownst to the crew or the controller, this put DHL flight 611 and Bashkirian Airlines flight 2937 on course to cross paths at the same height above an undefined point near Lake Constance on the Swiss-German border.
Now, at 23:34 and 24 seconds, First Officer Campioni said, “Excuse me, I’ll use the facilities,” and got up to go to the bathroom.
Eighteen seconds later, an automated voice called out, “TRAFFIC, TRAFFIC.” Captain Phillips’ attention was suddenly drawn to his TCAS display, where he saw an unidentified aircraft approaching from the right at approximately the same altitude. He watched it attentively, waiting to see if TCAS would issue a resolution advisory.
At exactly the same moment, the same automated voice called out “TRAFFIC, TRAFFIC” in the cockpit of the Tupolev.
“There, fucking traffic,” Instructor Captain Grigoriev said.
In the control center, Peter Nielsen suddenly noticed that the two planes appeared to be on a collision course. The Short-Term Conflict Alert light would have illuminated two minutes ago, but it wasn’t working, and Nielsen had noticed the conflict quite late. He quickly rolled his chair from the approach control station, where he had been speaking to the Aero Lloyd flight, back to the upper sector station. Leaning into the mic, he contacted the Tupolev and said, “Bravo Tango Charlie 2937, descend flight level 350, expedite, I have crossing traffic.”
“Descend!” Grigoriev immediately ordered.
The instant he said this, the TCAS computer, detecting an imminent collision, issued a resolution advisory, and the robotic voice called out, “CLIMB! CLIMB!”
Captain Gross was already pushing his yoke forward to descend when First Officer Itkulov, observing from the jump seat, called out, “Climb, it says!”
“He’s guiding us down!” Grigoriev emphatically replied.
It was a situation for which they had never been trained: a controller telling them to descend to avoid another aircraft, while TCAS simultaneously instructed them to climb. It would obviously be impossible to comply with both. So which order should they trust? Which took priority?
Meanwhile on the Boeing 757, Captain Phillips received an opposite resolution advisory. “DESCEND! DESCEND!” the robotic voice called out, and he immediately pushed his yoke forward to reach the target descent rate. The instruction came concurrently with Nielsen’s identical instruction to the Tupolev, causing him to miss this critical exchange. Both planes were now descending toward each other at a closing speed of more than 1,300 kilometers per hour.
Hearing the sound of the alarms, First Officer Campioni hurried back to the cockpit. Glancing out the window, he could clearly see the lights of the Tupolev at approximately their 2:00 position, blinking in the void. “Traffic right there,” he announced. But it was impossible to tell, without any visual reference point, whether the plane was above them or below them. All they could do was trust the TCAS resolution advisory.
But as flight 611 descended, the projected separation distance between the two planes wasn’t changing. “INCREASE DESCENT,” the TCAS commanded. Phillips pushed forward on his yoke even harder.
In the control center, Peter Nielsen hadn’t received any acknowledgement of his instruction to the Tupolev. “Bravo Tango Charlie 2937, descend level 350, expedite descent!” he repeated.
“Expedite descent level 350, Bravo Tango Charlie 2937,” Instructor Captain Grigoriev acknowledged.
For the pilots of the Tupolev, this second order removed any doubt about whom to obey. Captain Gross immediately pitched down even more, faithfully following the command to “expedite.”
Ten seconds later, Nielsen hurriedly added, “Ja, you have traffic at your two o’clock, now at 360.” But from the perspective of the Tupolev, the traffic was at their 10:00 position, not their 2:00 position, and his misleading transmission led to confusion in the cockpit.
“It’s going below us!” said Navigator Kharlov.
“Where is it?” Grigoriev asked, peering out the window.
“Here on the left side!” said First Officer Itkulov.
“INCREASE CLIMB!” came the robotic voice of the TCAS.
“It says ‘climb’!” Itkulov repeated. But they kept descending, accelerating through -1,800 feet per minute.
As the Tupolev pilots frantically tried to work out what to do, Peter Nielsen, thinking he had ordered the Russian jet out of harm’s way, slid his chair back over to the approach control station, where the Aero Lloyd flight was calling him yet again. At his other station, First Officer Campioni on the Boeing 757 could be heard announcing over the radio, “Dilmun six hundred, TCAS descent!” But Nielsen never heard him.
Aboard the 757, it suddenly became apparent that the Tupolev, which just a few seconds ago appeared far away, was rapidly closing on their position. “Descend!” First Officer Campioni shouted. “Fuck, descend hard!”
At the same moment, the Tupolev pilots saw the Boeing 757 hurtling out of the night, headed straight for them. “Oh shit,” Captain Gross exclaimed, hauling back on his control column and pushing the engines to full power. On the 757, Captain Phillips pushed his yoke all the way to the stop in a desperate attempt to dive. And for a moment, 71 lives hung in the balance.
But it was already too late. At 23:35 and 32 seconds, the vertical tail of the 757 slammed into the underside of the Tupolev’s left wing as it passed overhead.
“I told you it was coming from the left!” one of the Russian pilots managed to scream over the horrible roar of the impact.
Sliced nearly in two by the 757’s tailfin, its left wing ripped clean from its root, the Tu-154 began to disintegrate within seconds, spinning itself apart in a great cloud of fire. It rolled rapidly to the left, and then the fuselage failed and the plane broke in half, its cockpit and forward cabin folding back and ripping away, while the tail section and right wing, engulfed in flames, arced like a falling star across the night sky over Lake Constance.
On board the 757, the pilots felt a massive jolt, and then the plane yawed and rolled sharply as the loss of its vertical tail fatally compromised its directional stability. As it careened into this extreme maneuver, aerodynamic forces ripped off both engines, and the plane began to plunge from the sky, corkscrewing down into the dark forest below. The pilots likely fought until the end, but there was nothing they could do. About two minutes after the collision, DHL flight 611 plowed nose-first into a forest outside the village of Taisersdorf, instantly killing both crewmembers.
At the same time, local residents in the town of Überlingen and neighboring villages heard an explosion in the sky and looked up to see burning pieces of the shattered Tupolev raining down over an area encompassing more than 200 square kilometers. A dinner party near Owingen was interrupted when the flaming remains of the center section and right wing crashed down in the hostess’s rear garden. Nearby, the tail section slammed into a road and a field in front of a boarding school for disabled children, and about 300 meters away the severed cockpit fell to earth in an apple orchard. Other pieces of debris from both planes — the remains of the left wing, sections of the fuselage ceiling, a landing gear fairing, the tip of the 757’s stabilizer — fell like hail across a zone approximately 20 kilometers long.
As witnesses rushed outside, already struck with terror by the sight of the burning plane falling from 35,000 feet, they came across something even more horrible: the bodies of dozens of children, strewn for kilometers over streets, fields, and forests. The headmaster of the boarding school emerged to find about twenty dead children on his property; others found bodies in their yards, on the streets in front of their houses, and scattered in the fields around the shattered remnants of the fuselage. Not one among them had survived the fall — in fact, investigators would later determine that 40 of the 69 passengers and crew aboard the Tupolev were ejected from the plane before it hit the ground. This was a sight which would stay forever with those who witnessed it. The horror of a plane crash is bad enough when the victims are adults — but to be faced with such carnage wrought upon children is an experience which simply cannot be described.
Within about 15 to 20 minutes of the crash, a witness contacted Germany’s Federal Bureau of Aircraft Accident Investigation, or BFU, reporting a collision of two planes over Überlingen. Upon confirming that a crash had indeed taken place, the BFU launched one of the most significant investigations in the history of modern German aviation.
As dawn broke over Lake Constance, investigators were already on the scene, confronting a vast crash site unlike any they had previously encountered. Thousands of people worked to cordon off the area, locate wreckage, and recover human remains. It would ultimately take several days to find all the bodies, confirming a grim, self-evident truth: that none of the 71 people on board the two planes had survived. Among the dead were one Briton and one Canadian — the DHL pilots — as well as four Belarusians and 65 Russians. Forty-eight of them were children.
In the city of Ufa, home to most of the dead, the population was left in a state of shock. In addition to the talented artists and athletes, several of the victims were the children of high-ranking officials in Bashkortostan, including members of the administration of the President of the Republic. Local authorities declared a period of mourning; businesses shut their doors, festivals were cancelled, and radio stations only played sad classical music. One restaurateur who tried to put on a pop song was nearly run out of town, so intense was the city’s collective grief.
Meanwhile, by examining the wreckage, BFU investigators were able to conclude that the planes collided at an angle close to 90 degrees, and that the tail of the 757 sliced through the fuselage and left wing of the Tu-154 from underneath. The Tu-154 subsequently broke up in flight, while the 757 lost control and crashed nearby. But the mystery only deepened: how could two relatively new airplanes, both equipped with the latest Traffic Collision Avoidance Systems, collide in the tightly controlled airspace of Central Europe? Western media, apparently citing the Swiss air traffic control agency, suggested that the Russian pilots had failed to follow the controller’s instruction to descend. Russian authorities lashed out at the reports, implying that the controller was at fault for telling them to descend in the first place. It was only several days later that Swiss authorities admitted that controller Peter Nielsen had only warned the Tupolev crew 50 seconds before the collision, and that they appeared to have complied within a relatively short period.
The answers to the mystery lay in the planes’ black boxes, which recorded the critical conversations on both flight decks in the minutes leading up to the collision. The BFU noted that both flight recorders on the 757 cut out nine seconds after it hit the Tupolev, when the engines separated from the wings, leading to a loss of power. The Tupolev’s flight data recorder also ceased operation three seconds after the collision when the fuselage broke in two, but investigators were horrified to discover that the cockpit voice recorder, mounted in the cockpit and powered by a backup battery, continued to record for a further two minutes as the severed cockpit plunged toward the ground.
Their disturbing final contents aside, the black boxes revealed the fundamental misunderstanding which led to the crash. Unaware that TCAS was about to issue a resolution advisory, Peter Nielsen ordered the Russian crew to descend, while TCAS simultaneously told them to climb and instructed the 757 to descend. The Russian crew, faced with a choice between the controller and their TCAS, chose to obey the controller and descended directly into the path of the 757. This raised three primary questions: could either crew still have prevented the collision, why did the Russian crew choose not to obey their TCAS, and why did the controller allow the situation to become so critical before intervening?
To answer the first question, investigators carried out a second-by-second analysis of the last minute of the two flights, from the time the crews became aware of a conflict up until the moment of the collision.
It should be noted that both aircraft were operating on the same radio frequency, and in theory could have heard every relevant ATC communication. But a series of timing coincidences prevented either crew from realizing what was taking place. Captain Phillips on the 757 might have heard Nielsen’s order for the Tupolev to descend had it not come at exactly the same moment as his own TCAS resolution advisory, which obviously commanded greater attention. First Officer Campioni wasn’t in the cockpit at the time and could not have heard it either. The same thing happened all over again during the controller’s second order for the Tupolev to descend, which corresponded temporally with the order from Phillips’ own TCAS to “increase descent.” In this dynamic environment, Phillips’ brain would have prioritized the more immediate command from the TCAS before considering the overall situation. And again, Campioni hadn’t put his headset back on yet and couldn’t have heard the transmission.
Subsequently, the 757 crew waited 23 seconds to inform air traffic control that they were in a TCAS descent, a delay which some felt was inappropriately long. But it seemed that Captain Phillips was primarily concerned with achieving the required rate of descent, and First Officer Campioni was neither in his seat nor wearing his headset until shortly before the transmission was in fact issued. The coincidental fact that Campioni decided to go to the bathroom right before the TCAS came to life evidently contributed to the lateness of the message, and in fact had he been in the cockpit throughout the event he might have been able to inform Nielsen in time to avert the collision, but that this did not happen could only be put down to random chance.
Although Nielsen didn’t hear the 757’s “TCAS descent” call, it was recorded on the CVR of the Tupolev, and yet none of her crewmembers reacted either. Investigators theorized that amid the animated conversation and high stress levels in the Tupolev cockpit, the pilots simply didn’t hear it. This was the only communication which occurred between ATC and the 757 during the entire time the Tupolev was in Zürich airspace, hence there was no other opportunity for the crew to hear what the 757 was doing.
The BFU also noted that a misleading cue from the controller could have convinced the crew that descending was indeed the only way to avoid the collision. When Nielsen reported that the crossing traffic was at flight level 360 — that is, 36,000 feet — it was actually passing through 35,600 feet and descending rapidly. By placing it at 360, he put it above the Tupolev, which had already begun its own descent a few seconds earlier, when it was actually slightly below. This discrepancy occurred because Nielsen’s radar display only updated once every 12 seconds, and was still showing the 757 at 35,900 feet when he issued the transmission, rendering him unaware that it was descending.
Based on statements made on both cockpit voice recordings, it appeared that both crews were able to visually locate the other aircraft from an early stage, and in the case of the Tupolev this occurred even before the resolution advisory was issued. The blinking anti-collision lights against the moonless sky were in fact quite easy to see, even from a great distance, but judging the relative height of the planes and their future trajectories under such conditions was completely impossible. The human brain relies on points of reference to determine an object’s relative motion, but the conditions that night presented none. Only in the last few seconds before the collision would the planes have been large enough in the field of view for their respective crews to have understood their relative positions. Consequently, both crews did take evasive actions about two or three seconds before impact, but by then it was too late for their inputs to take effect.
Considering these facts, it could not be said that either crew was in a good position to avoid the other plane, either by visually anticipating a collision or by understanding the situation through overheard ATC communications. The more important question, therefore, was why the Tupolev pilots chose to obey ATC over their TCAS.
In fact, this decision was deeply rooted in both the history of TCAS and the unique circumstances of aviation in Russia. It was a decision born not of faulty judgment, but of a fundamental cultural misunderstanding between the Russian crew and the Western engineers and regulators who designed the TCAS and then mandated its use.
Although traffic collision avoidance systems had been required in the United States since 1993 and in the European Union and the Middle East since 2000, at the time of the accident they were not required in Russia. In fact, the only reason the accident Tu-154 even had a TCAS was so that it could fly to destinations in Europe — after all, back home in Russia, where most traffic wasn’t equipped with the system, it would have been of little use. Training on the system was therefore quite sparse. Bashkirian Airlines didn’t have access to a Tu-154 simulator equipped with TCAS, and it’s not clear such a thing even existed. In the absence of an appropriately outfitted simulator, the pilots only received theoretical training on TCAS, followed by a brief demonstration of the system in a plane parked on the ground. Furthermore, the pilots gained minimal TCAS experience in the line of duty because they rarely flew to Europe — in fact, so far in 2002 the two captains put together had a mere 16 flights into airspace where TCAS was active. They almost certainly had never encountered so much as a TCAS traffic alert, let alone a full-on resolution advisory, and this would have been their first time responding to one, either in training or in real life.
In addition to their unfamiliarity with the system, the airline’s Tu-154 operating manual contained language which contradicted that used by the manufacturer and undermined the very purpose of TCAS. As it was conceived in America, TCAS is a last line of defense, a surefire way to prevent a collision if the principles of air traffic control and “see and avoid” should prove inadequate. As such, there is no circumstance under which a TCAS resolution advisory should be disregarded, as its very activation implies that other means of collision avoidance have already failed. In fact, guidance issued by the US Federal Aviation Administration explicitly stated that a TCAS resolution advisory overrides even an order from air traffic control. But most everywhere else, the rules were nowhere near as clear-cut. Official guidance from the International Civil Aviation Organization, or ICAO, which signatory nations use to create their own regulations, did not say what to do if TCAS and ATC issued conflicting avoidance instructions. Similarly, European regulations failed to cover this scenario.
But in Russia, the regulations not only lacked clarity, but appeared to directly contradict those suggested by ICAO. Notably, the Bashkirian Airlines Tu-154 operating manual said the following: “For the avoidance of in-flight collisions … the visual control of the situation in the airspace by the crew and the correct execution of all instructions issued by ATC [is] to be regarded as the most important tool. TCAS is an additional instrument which ensures the timely determination of oncoming traffic, the classification of the risk and, if necessary, planning of an advice for a vertical avoidance manoeuvre.” And after minimizing the importance of TCAS as a last line of defense, the manual went on to say, “The ATC service [is] to be the basic system for the collision avoidance. Nevertheless, in case of no link with ATC, the TCAS will help the crew avoid a collision,” implying that TCAS only needs to be followed in the absence of input from ATC. This advice was in line with the policies that existed under the Soviet Union, when controllers wielded a level of absolute authority that they never held in the West, but it did not correspond well to modern principles of traffic separation.
In practice, the idea that anything can override a TCAS resolution advisory defeats the purpose of the system, which is to prevent a collision after all other means of safe separation are exhausted. But the pilots of the Tu-154 certainly never considered it this way, and in their minds there would have been little ambiguity as to the precedence of Nielsen’s command to descend over the TCAS instruction to climb. This logic would have fallen apart had they recalled that TCAS would send an opposite instruction to the other plane, but their experience with the system was so limited that they probably forgot. First Officer Itkulov, who repeatedly called attention to the TCAS order to climb, may have remembered this fact, but he never clearly articulated it, and no one listened to him anyway.
It is also worth noting that the ATC order, unlike the TCAS resolution advisory, corresponded to the pilots’ conception of the way traffic conflicts are typically resolved in Russia. While the airplane on the left is expected to give way under Western right-of-way rules, Russian rules hold that both planes must change course, with the plane on the left — the 757 — climbing, while the plane on the right — the Tupolev — descends. In a TCAS environment, right of way is not very meaningful, but for these pilots it would have been the acting principle during 95% of their careers, and it would have reinforced the apparent correctness of Nielsen’s order.
It was now apparent why the Tupolev pilots made their decision, and that this decision was entirely in line with their training. The largest remaining question then was why Peter Nielsen allowed the situation to escalate to the point of TCAS becoming involved in the first place.
The roots of Nielsen’s predicament go back to the very structure of the Swiss air traffic control system. For most of history, Switzerland’s air traffic control services were run by the state, but in 2001 this service was privatized, becoming an independent company known as Skyguide. Although the government still owned 99% of the shares in Skyguide, it did not receive government funding and was expected to support itself financially through contracts. This reorganization came at a time when air traffic controllers were in high demand across Europe due to an estimated 12% continent-wide shortfall in ATC personnel. Consequently, in the year before the accident, the number of controllers on duty in Zürich during the night shift was reduced from three to two.
Back when three controllers were present, it had become common practice for one controller to take an extended break during the middle of the night. This habit was not officially sanctioned but had been tolerated by management for years. But when the standard night shift roster was reduced to two controllers, this practice continued, even though it left just one controller on duty through the middle of the night shift. This violated Skyguide rules, which required separate controllers to work the approach and upper sectors, but given that all nearby airports were closed to landing traffic by 23:00, no one seemed to think it would be a big problem if there wasn’t a dedicated approach controller during this time of night.
Most of the time, the workload at night was low enough that one controller could handle it without difficulty, and Peter Nielsen had become accustomed to this arrangement. But the addition of the maintenance work significantly increased his workload by disabling systems that would normally assist him with his duties. In combination with the unexpected arrival of the Aero Lloyd flight to Friedrichshafen, this directly contributed to the accident. Under normal circumstances, it would have been easy enough for Nielsen to call the Friedrichshafen tower to hand over control of the Aero Lloyd flight, then return his attention to the upper sector. But with the direct phone lines down, he and his assistant had to search for alternative means of communication, which occupied his attention for the first three out of the five minutes leading up to the collision. However, calling the approach controller, who was likely asleep in another part of the building, would have been even less efficient.
It also could not be ignored that the optical Short-Term Conflict Alert, which would normally have drawn his attention to the developing situation, was not working due to the disconnection of the main computer. And on top of this, the fact that the planes would cross paths in between scheduled waypoints meant that it was not obvious that their flight plans would conflict until the planes began to visibly converge on radar.
By the time Nielsen noticed the conflict, the planes were already closer together than the minimum allowed by regulations, and even if he had successfully averted the collision at that moment, this fact alone meant there would probably have been an investigation. At this point, he decided to contact the plane to which he had spoken most recently, which was the Tupolev, and because its flight plan showed it was scheduled to do so soon anyway, he chose to instruct it to descend. These spur of the moment decisions planted the seeds of disaster, but Nielsen had no way of predicting the confusion his order would cause. The TCAS resolution advisories had not yet been issued, nor could he have been aware that they would be issued less than one second after the end of his transmission. Although controllers are prohibited from issuing instructions which contradict a TCAS resolution advisory, the pilots must tell the controller about the advisory before this rule is applicable, and neither crew did so until much later.
Once the Tu-154 crew had acknowledged his instructions to descend, Nielsen believed that the conflict was resolved. If he had watched the radar screen a few seconds longer, he would have noticed the 757 begin to descend as well, but before he could do so, the Aero Lloyd flight called him again. He spent the next 30 seconds or so informing this flight how to contact Friedrichshafen without an official control handover having taken place. Around the time that this conversation began, an aural alert sounded in the control center, calling out “CONFLICT, CONFLICT,” to warn that the distance between the planes was less than 6.5 nautical miles. However, no one present in the room could recall hearing the alarm, and even if Nielsen had noticed it, he would have disregarded it, believing that he had already put the planes on course to correct the situation.
Almost concurrently with these events, the 757’s first officer called to report that they were in a TCAS descent, but because he was at a different work station talking to a different plane, Nielsen didn’t hear the transmission. At that point, disaster became all but inevitable. In fact, by the time Nielsen next turned his attention back to the upper sector, the collision had already taken place. Just 50 seconds had passed since his first instruction to the Tupolev.
One final chance to prevent the collision was also foiled by the maintenance work. Heartbreakingly, controllers in neighboring Karlsruhe saw the collision coming, but they did not have the authority to speak to planes in another sector without permission from the responsible controller. The Karlsruhe controllers tried several times to call Nielsen in the minute before the crash, but the landlines were down and they couldn’t get through. By the time they gave up on this effort, it was too late to prevent the crash even by breaking the rules. The controllers were forced to watch, helpless, as the two planes collided and then disappeared from radar, knowing that dozens of people were dying before their eyes, and that there was nothing they could do to save them.
Having already absolved the two crews of blame, the BFU was forced to conclude that Nielsen didn’t hold any personal responsibility for the disaster either — every decision he made was relatively sensible under the circumstances, with the exception of his mistaken report that the 757 was at the Tupolev’s 2:00 position. However, this slip-up did not contribute to the accident, since the Tu-154 crew already had the 757 in sight.
In the end, systemic deficiencies at the Zürich control center prevented Nielsen from doing his job safely and led more or less directly to the disaster. Skyguide had come to tolerate single-controller operations without conducting any risk assessment, believing that the practice was common throughout Europe. Skyguide also did not assess the potential risks involved in the maintenance work, and it failed to inform controllers of the work’s potential side effects. It was this apparent lack of interest in safety which created the circumstances for the accident to occur. That night, Nielsen was doing the jobs of three people — supervisor, upper sector controller, and approach controller — with inadequate information and multiple inoperative systems. Such a situation should never be allowed to develop, and Skyguide ultimately bore responsibility for the fact that it did.
In its final report on the accident, the BFU painted a picture of a series of wild coincidences which, in the presence of systemic deficiencies, led to disaster. But to come away from the report believing that the Überlingen collision was a one-off would be incorrect. In fact, the lack of clarity in many parts of the world about the relative authority of an ATC order and a TCAS resolution advisory was already known to the industry. In January 2001, this very same loophole nearly led to what would have been the worst air disaster of all time. As a Japan Airlines Boeing 747 with 427 people on board climbed toward 39,000 feet after takeoff from Tokyo, an overwhelmed trainee controller allowed it to embark on a collision course with another Japan Airlines flight, a DC-10 carrying 250 passengers and crew. As the planes drew near each other, the controller instructed the 747 to descend, but three seconds later, its TCAS instructed it to climb.
Trusting the controller over the automated system, the pilots of the 747 put their plane into a descent, unaware that the DC-10, having received a TCAS advisory to descend, was doing the same. Amid the confusion, the trainee controller’s supervisor attempted to order the 747 to climb, but her transmission was lost in the chaos of the moment. As the two planes descended directly toward each other, the crew of the 747 suddenly caught sight of the DC-10 and executed a last-second evasive maneuver, pitching steeply downward in a desperate effort to avoid a collision. Seconds later, the 747 passed just 135 meters underneath the DC-10, avoiding disaster, but only by the narrowest of margins.
The evasive maneuver was so abrupt that flight attendants, passengers, and loose objects were thrown into the ceiling, only to crash down again two seconds later. The violent change in direction injured 100 people, nine of them seriously, including a woman who suffered a broken leg. Damage to the cabin interior, particularly the ceiling, was extensive; most notably, a drinks cart, shown above, was thrown through the cabin ceiling and into the attic behind the first class lounge, where it remained for the rest of the flight. In the end, the 747 safely returned to Tokyo, and the injured passengers were released for medical treatment, many of them unaware that they had come frighteningly close to death.
Within a short time after the near miss, it became apparent that one plane had obeyed its TCAS while the other followed a conflicting instruction from ATC. The potential danger of this type of misunderstanding should have been plainly apparent. But by the time of the Überlingen disaster 17 months later, nothing had fundamentally changed.
Part of the problem was that the system by which such changes make their way around the world is very slow-moving. Japanese investigators would have had to issue a recommendation to the International Civil Aviation Organization; ICAO would then have had to adopt the new guidance; this guidance would have to have been propagated to signatory nations; those nations would have had to agree to adopt the new wording into their own regulatory systems; and then the new concept would have had to be passed on to pilots during recurrent training. Even if ICAO had immediately begun proceedings to clarify the relative precedence of TCAS resolution advisories and ATC commands (which it does not seem they did), it’s not clear that the changes would have reached the Bashkirian Airlines crew in time to prevent the accident. This is especially true considering that Russia’s TCAS-related regulations already diverged even from the original, flawed ICAO guidance, suggesting that bringing Russian rules into compliance would be quite difficult. On the other hand, had the two Japanese airliners actually collided, almost assuredly resulting in the deaths of an unprecedented 677 people, it’s quite likely that no one would ever make the same mistake again, even if ICAO did nothing. In this way, it becomes apparent how fatal accidents command much swifter change than near misses even in the absence of any conscious decision by regulators to treat them as such.
In the years since the disaster over Überlingen, prescribed responses to TCAS resolution advisories have been standardized around the world, systems have been introduced which can alert controllers directly whenever a resolution advisory is issued to an aircraft, and TCAS is now capable of reversing its commands if one aircraft does not comply. Thanks to these changes, it is unlikely that a similar accident will happen again. And 20 years later, the Überlingen disaster remains the only major midair collision involving two planes with properly operating traffic collision avoidance systems.
On the legal side, fault for the accident was officially placed on Skyguide, and several Skyguide officials were charged with manslaughter. Although they were found guilty, no real punishment was handed down — three Skyguide managers who tolerated rule violations were given suspended prison sentences, while a fourth was ordered to pay a small fine, a judgment widely considered inadequate. However, the company itself was forced to pay compensation to the victims and take corrective actions to improve its safety culture. It has managed Swiss airspace without incident ever since, as a vase of white flowers in memory of the victims permanently watches over the work station where Peter Nielsen once sat, forever reminding controllers of their responsibility to the public.
And the story of the Überlingen disaster should have ended there, with the necessary changes having been made to ensure the safety of future air travelers. But in fact, one tragic twist remained in store.
Vitaly Kaloyev, the Russian architect, was waiting for his family in the airport in Barcelona when he received the unimaginable news: their plane had crashed, and there were no survivors. Stunned by the loss of his wife and two young children, Kaloyev immediately traveled to Germany, where he arrived in Überlingen the day after the accident. Consumed by grief, he joined the search for the remains of his four-year-old daughter Diana, against the recommendation of authorities. By some stroke of luck, her body was found intact, lying on the forest floor beside the pearl necklace Kaloyev had given to her. She was the youngest of the 71 victims, not even old enough to begin school. It seemed beyond cruel that she should lie dead in a forest in Germany while her bereaved father wept over her lifeless body.
Kaloyev subsequently returned to his native Vladikavkaz, where he buried his wife and children side by side and erected a sprawling shrine to their memory. It is never easy to move on from such a profound grief, but Kaloyev found it especially difficult. He could be found lingering by the memorial at any time of day and in any weather, for months on end. He barely slept or ate, and how could he? Everything which gave his life meaning had been taken away.
As the events which led to the crash started to become clear, Kaloyev became fixated on a singular goal: to convince Skyguide to apologize for its role in the accident. He attended gatherings of victims’ relatives and press conferences in Germany, where he confronted Skyguide officials and demanded that they apologize. But Skyguide, embroiled in lawsuits over the accident, had instructed its spokespeople not to admit any fault until a verdict had been handed down. Instead, the company offered him a total of 160,000 Swiss francs in compensation for his loss, on the condition that he refrain from any lawsuits. This is standard procedure in the West, and Europeans and Americans tend to respond to the practice by rolling their eyes, muttering obscenities about the company in question, and then suing to increase the payout. But in the cultures of the North Caucasus, there is an expectation that such a high-stakes dispute will end with either an admission of guilt and a request for forgiveness, or with justified revenge by the injured party. Not only would a failure to apologize be considered a damnable provocation, but the failure of the injured party to respond proportionately would be considered a dereliction of his duty as a man.
Kaloyev soon changed course and asked instead if it would be possible to meet Peter Nielsen, to speak with him and convince him to apologize instead. But this too was denied — Nielsen was in no fit state to speak to the unstable relative of a Überlingen victim. And so Kaloyev drifted back and forth between Germany and Vladikavkaz, growing progressively angrier as the legal proceedings dragged on without any conclusion. Many in Russia felt that the slow pace of justice amounted to a coverup, and Kaloyev agreed. This was another cultural misunderstanding — in Russia, following an accident, everyone involved is usually arrested immediately and then released if they are not found at fault. In contrast, Western nations don’t typically arrest aviation professionals for making mistakes, unless gross negligence can be demonstrated, and company officials will only be charged after lengthy investigations. Kaloyev, however, had no patience for this lenient approach, and in late 2003 or early 2004, he decided to take matters into his own hands.
Having hired a private investigator to find Peter Nielsen’s address, Kaloyev arrived in Zürich in February 2004 and checked into a hotel. A few days later, on the 24th of February, he traveled to Nielsen’s house, armed with a 22-centimeter jack knife and photographs of his dead family members.
Initially, Kaloyev sat down in Nielsen’s garden, seemingly unsure what to do. When Nielsen eventually emerged to investigate, he did not respond kindly to the presence of Kaloyev on his property. Nielsen had been affected deeply by the crash, to the point where he required medical treatment for acute PTSD, and this unexpected visitation only rubbed salt in his wounds. A brief, unfriendly conversation ensued. Kaloyev then got up in Nielsen’s face and showed him the photos of the bodies of his children. Backed into a corner, Nielsen pushed them aside. It was at that moment that Kaloyev apparently snapped: blinded by rage, he stabbed Nielsen several times in the chest, mortally wounding him. He then ran away down the street, blood still dripping from his reddened hands, as Nielsen died in the arms of his family.
The following day, police arrested Kaloyev in his hotel room and charged him with premeditated killing. Public reactions to the revelation of the murder varied significantly. Europeans were largely outraged, while the response within Russia was much more mixed. Many people, while denouncing the murder, nevertheless sympathized with Kaloyev’s plight. A significant minority outright endorsed the killing, which drew heated condemnation from the other side, including from another man who also lost his entire family in the crash, who said he could see no justification for Kaloyev’s actions.
In court, Kaloyev initially denied intending to kill Nielsen, but could not explain why he had brought the knife if his only goal was to talk. Later, he expressed no remorse for the murder, which he considered to be justified under his North Caucasus code of honor. In the end, a Swiss court, considering the mitigating circumstances, sentenced him to eight years for manslaughter. Even this relatively light sentence was seen by many Russians as too harsh, and the government began to put pressure on its Swiss counterpart to reduce the punishment. Switzerland ultimately caved under the pressure, and Kaloyev was released from prison without a clear explanation in 2007, having served only two years out of his eight year sentence.
Kaloyev returned home to a triumphant welcome, where he was ushered off the plane by an adoring crowd of Vladikavkaz residents and members of the pro-Putin youth group Nashi. Although Russians overall were split on whether he was a hero or a criminal, his home province did not hesitate to pull out all the stops to celebrate his release. People cheered for him in the streets and stores refused to take his money when he shopped for groceries. Journalists selected him as Vladikavkaz’s “Man of 2007,” and the leader of North Ossetia-Alania appointed him Deputy Construction Minister for the autonomous republic. “I don’t really take offense at people who call me a murderer,” Kaloyev told the Los Angeles Times upon his return. “People who say that would betray their own children, their own motherland… I protected the honor of my children and the memory of my children.”
All of this fanfare ignored the fact that Nielsen was never found at fault in the accident in the first place. As Russian nationalists hailed Kaloyev as a hero for carrying out “justice” on behalf of the victims, few could explain what Nielsen had actually done wrong, besides issuing a relatively late warning to the Tupolev crew. The way this particular segment of Russian society reacted to the crash and the murder was an ugly reflection of a national tendency to blame whoever happens to be present at the moment of a tragedy, while those responsible for creating the unsafe condition go unnamed and unpunished.
No doubt buoyed by his celebrity status, Kaloyev eventually recovered from his crippling grief, remarried, and had two more children, who are both three years old as of this writing. He retired from his post as Deputy Construction Minister in 2016, but he continues to live a fairly comfortable life in Vladikavkaz. In contrast, Nielsen’s family, hurt beyond words by Kaloyev’s callous and misguided revenge, returned to their native Denmark and retreated from the public eye.
In the end, the Überlingen disaster was not the result of one man’s split-second decisions, but the inevitable product of a deficient system — of an air traffic control company which paid too little attention to safety, and of international and national-level regulators who were too slow to correct a glaring flaw in the rules which keep airplanes apart. It is also a reminder that cultural norms play as much of a role in aviation safety as they do in our perception of justice. As the two planes sped toward each other that night, a sequence of events took place in which eight people in three different locations all tried to avert disaster as best they could, only for their divergent expectations to steer them inexorably into the jaws of catastrophe. And as so often seems to happen, the most innocent among us paid the price, leaving in their wake a trail of broken dreams and broken families. Shedding more blood did not and cannot make those dreams whole again. They have vanished with the children of Ufa, like so many tears in the rain.
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