Cleared for Catastrophe: The crash of Inex-Adria Aviopromet flight 1308
On the first of December 1981, a charter flight carrying Yugoslav tourists to the French island of Corsica clipped the top of a mountain and plummeted into a ravine, killing all 180 passengers and crew in one of France’s worst air disasters. The shattered pieces of the McDonnell-Douglas MD-82 were found clinging to the precipitous mountainside high above the village of Petreto-Bicchisano, where French and Yugoslav investigators could reach them only by helicopter. From the mangled wreckage they pulled the plane’s two black boxes, which had preserved the tragic last moments of a holiday gone awry. The investigators found that as the fully loaded airliner descended into the city of Ajaccio, a series of misunderstandings developed between the captain and the air traffic controller. Split second choices of words formed diverging mental pictures of the situation, leading the controller to clear the flight to descend straight into the mountain. But who was really at fault? What should be done to prevent it from happening again? The lessons of an eerily similar accident in the United States seven years earlier would provide some of the answers.
Throughout much of the latter half of the 20th century, Yugoslavia acted as a bridge between the East and West. As one of the leaders of the non-aligned movement, the country’s communist government maintained cordial relations with both NATO and the Soviet Union, making Yugoslavia a growing destination for tourists from both sides of the Iron Curtain. At the same time, the country’s position allowed its own people to travel to Western Europe far more easily than most of its communist neighbors. Between the 1960s and the 1980s, the result of these opportunities was a booming air charter industry, and at the center of that industry was Inex-Adria Aviopromet. Founded in 1961 as the national airline of the Yugoslav Republic of Slovenia, the airline found a niche ferrying tourists to and from Yugoslavia via on-demand charter flights organized by both domestic and foreign travel agencies. By the 1980s, it had also introduced scheduled flights within Yugoslavia and had grown a respectable fleet of Western-built jets, a luxury not afforded to similar state-run carriers in the Warsaw Pact.
In May of 1981, Inex-Adria Aviopromet purchased three brand new McDonnell Douglas MD-82 twin rear-engine jets. An updated and stretched version of the earlier Douglas DC-9, the MD-80 series had just been introduced the previous year, and the aircraft represented a significant step up for the airline.
Later that year, Inex-Adria was approached by Kompas, a travel agency based in the Slovenian capital of Ljubljana, to cater to a promotional event planned for the first of December. In celebration of a Yugoslav national holiday, Kompas planned to take 130 tourists to the French Mediterranean island of Corsica for a scenic tour of the city of Ajaccio, then return them to Ljubljana later that same day. Because the number of tourists was slightly too large to fit them comfortably onto a regular DC-9, Inex-Adria decided to provide one of its new MD-82s, which would carry everyone with plenty of room to spare. The extra seats were offered to employees of Inex-Adria and Kompas as well as their families, which resulted in an additional 43 passengers beyond those originally booked on the flight. Because the trip to Ajaccio would be performed out and back in the same day, none of the passengers had checked bags, so the airline was able to fill the plane to capacity without impinging on its weight limit.
Early in the morning of the 1st of December, the passengers and crew gathered at Ljubljana’s Brnik Airport for the flight to Corsica. The plane was so packed with people that small children had to be stuffed together two to a seat; Inex-Adria employees flying as passengers were assigned to the flight attendant seating areas; and the airline mechanic — on board to service the plane in Ajaccio — had to be booked in the cockpit jumpseat. In addition to no less than 173 passengers, there were also seven crewmembers, including two pilots, four flight attendants, and the mechanic, totaling 180 people on board — about as many people as you could conceivably jam into an MD-82, which even in a single-class configuration was not rated for more than 172 passengers.
In command of the flight were Captain Ivan Kunovic and First Officer Franc Terglav, both of whom were experienced pilots; however, as would be expected with such a new aircraft, neither had more than about 300 hours on the MD-82. Captain Kunovic had just gotten out of training on the type in August; Terglav, in June. Nevertheless, they already loved the airplane, and they were just as excited for the trip as the passengers — First Officer Terglav had even brought his young son Tomaz along to check out the plane and see the sights in Ajaccio.
Shortly after 7:40 a.m., Inex-Adria flight 1308 departed Ljubljana for the approximately 90-minute flight to Ajaccio. Home to about 70,000 people, Ajaccio is the largest city on the island of Corsica and capital of the department (province) of Corse-du-Sud. The island’s largest airfield, Ajaccio-Campo dell’Oro Airport, is located just east of the city on a strip of flat land next to the coast with hills on three sides. That day, the weather near the airport was poor: much of Corsica’s mountainous interior was covered by a thick layer of cloud with the tops at about 7,000 feet, accompanied by powerful winds gusting to more than 130 kilometers per hour at middle elevations.
As flight 1308 cruised over Italy, the crew maintained a party atmosphere, allowing passengers to stand in the open cockpit doorway and ask questions about the plane. Later on, the mechanic went back to the passenger cabin so that First Officer Terglav could invite his son Tomaz up to sit in the cockpit. At 8:31, with Terglav’s son sitting in the jumpseat, the crew received clearance to begin their descent from 33,000 feet. As the pilots went over the speeds they would use during the approach, the child could be heard asking, “Are we going down?”
“We are going down,” Terglav explained.
To this, Captain Kunovic added a joke, somewhere along the lines of “we haven’t left a single plane up here yet.” Like the fun uncle he clearly aspired to be, he went on to pester him with a needling comment about his lack of a girlfriend.
As the descent over the island continued, the pilots ran through their approach briefing — most of it, at least. Twice, young Tomaz interrupted them to point at various objects outside the windows, including a mountain that he thought resembled the Matterhorn. Eventually, Kunovic and Terglav managed to finish going over the plan for the approach to Ajaccio, which they would be performing for the first time. The complex approach pattern for the two runways would begin by flying to the Ajaccio (AJO) VOR, or VHF Omnidirectional Range, a radio beacon south of the airport. They would then enter a holding pattern in order to lose altitude before looping back to AJO, where they would roll off on a heading of 247 degrees, along a route referred to as the 247-degree radial of AJO. Flying southwest, they would cross over the extended centerline of the northeast-pointing runway, conduct a 320-degree left orbit, and line up to land using the instrument landing system. For landing on runway 03, they would go straight in; to land on runway 21, the same runway in the opposite direction, they would descend until they could see the airport, then circle around and land from the other side. For most of the approach, they would be essentially on their own, as Ajaccio-Campo dell’Oro Airport lacked radar to help the controllers keep track of the positions of incoming planes.
After leveling off at 11,000 feet, flight 1308 neared the AJO beacon from the northeast and prepared to enter the holding pattern. At 8:47:10, Captain Kunovic opened communication with the Ajaccio approach controller. “Bonjour Ajaccio,” he said. “Adria JP 1308, we are level one one zero approaching Ajaccio VOR and further descent.” Kunovic expected that the controller would clear them down to a lower altitude, as the previous controller had been doing ever since the plane left 34,000 feet.
“Juliet Papa 1308, Ajaccio approach, good morning,” the controller replied. “Number one in approach, you maintain one one zero until you reach Alpha Juliet Oscar VOR: it will be for a procedure from the VOR, QNH one zero zero nine, QFE one zero zero eight; surface wind is two eight zero degrees for twenty knots. Runway two one in use, you report over Alpha Juliet Oscar VOR, and then descending over Alpha Juliet Oscar VOR.”
Most of this message was just standard information, such as altimeter settings (QNH and QFE) and weather information. But the phrase “it will be for a procedure from the VOR” was particularly noteworthy. The controller meant to give permission for flight 1308 to fly the standard approach beginning from the AJO VOR (as described earlier), and asked that the crew report over AJO while both entering and leaving the holding pattern, so that he would have some idea of their position. Critically, however, he failed at any point to use the word “cleared.” Without an obvious cue that they were “cleared for approach” — that is, cleared to fly the path depicted on their charts — the crew expected to be given further instructions about where to fly.
A misunderstanding had now developed: Kunovic expected to receive further descent clearance after reaching AJO, because if they stayed at 11,000 feet for too long, they would come in too high; the controller, on the other hand, felt that he had cleared flight 1308 to perform the approach and that the flight crew were free to descend to whatever altitude was suggested on their approach chart.
At 8:49:31, Captain Kunovic reported that flight 1308 was over AJO and “in holding.” The controller, not believing that he needed to give any further instructions, simply replied, “Roger, report leaving Alpha Juliet Oscar on radial two four seven for final approach,” reiterating his earlier request that flight 1308 report leaving the holding pattern.
But this wasn’t what Kunovic wanted to hear. “Okay sir,” he said, “we are just over Ajaccio VOR and we are requesting further descent.”
The next message that the controller was expecting to hear from flight 1308 was a position report over AJO on the 247-degree radial, not another request for descent clearance. This led to a second, even more critical misunderstanding.
Most pilots who were familiar with landing at Ajaccio took a shortcut during the approach: if they initially neared AJO at a low enough altitude, they would skip the holding pattern entirely and roll out directly onto the 247-degree radial. However, this was the first time Kunovic and Terglav had flown to Ajaccio and they didn’t know about this technique; instead, they were faithfully following their approach chart, which called for a holding pattern regardless of whether one was actually necessary. But the controller didn’t know any of this. When Kunovic radioed a second time that he was over AJO requesting a descent, the controller assumed that he was planning to skip the holding pattern, as most pilots did, and was therefore already reporting his turn off AJO onto the 247-degree radial. As a result of this incorrect assumption, the controller said, “1308, you are cleared to descend three thousand, QNH one zero zero nine, on the radial two four seven Alpha Juliet Oscar, and you report leaving Alpha Juliet Oscar.”
“Roger, will do,” Kunovic replied. “We are leaving one one for three thousand, radial two forty seven, out of one one zero.” Here Kunovic again compounded the misunderstanding by mixing together his readback of the clearance with descriptions of his actions. “We are leaving one one for three thousand” was a description of what they were currently doing, while “radial two forty seven” was an acknowledgement of where they would next report their position. By stringing the two items together, he made it sound as though they were already on the 247-degree radial of AJO, affirming the controller’s decision to clear them down to 3,000 feet.
This clearance down to 3,000 feet carried with it a hidden danger. According to the pilots’ approach chart, the minimum safe altitude on the holding pattern around Ajaccio was 6,800 feet. But the pilots had missed the minimum safe altitude during their approach briefing due to the repeated interruptions from the child in the cockpit, and they apparently believed that the controller would not clear them to descend to 3,000 feet unless it was safe to do so.
On top of this, their approach chart might have misled them about the proximity of high terrain to the holding pattern. The minimum safe altitude of 6,800 feet had been designed to keep planes clear of the 4,587-foot Mont San-Pietro, a peak located 24 kilometers southeast of the airport, but the chart didn’t make that obvious.
The instructions for the holding pattern specified that they should proceed outbound from AJO for one minute before returning. This meant that the distance covered while in the holding pattern would vary depending on the speed of the aircraft. In the holding pattern around AJO, flying at 210 knots (389km/h) — the maximum allowed speed in the holding pattern according to the approach chart — will cause an airplane to overfly Mont San-Pietro. However, the depiction of the size and shape of the holding pattern on the approach chart was based off of a speed of 150 knots, a fact which was not mentioned anywhere. As a result, the depiction was considerably smaller than the route which would be traversed by an airplane flying at the maximum speed. This depiction didn’t show the holding pattern going anywhere near Mont San-Pietro, even though at 210 knots the mountain would be directly underneath the flight path. As a result of this misleading depiction, the crew might have thought that there was no terrain in the area that would prevent them from descending to 3,000 feet as cleared. But flight 1308 entered the holding pattern at slightly above 210 knots and never once dropped below this speed from that point on, meaning that they would swing far enough to the east to cross Mont San-Pietro. The stage was now set for disaster.
At 8:50:19, just seconds after receiving the descent clearance, Captain Kunovic decided to add, “We are in holding over Ajaccio, call you inbound on radial two forty seven.” Perhaps he wanted to be extra sure that the controller knew they were in the holding pattern.
But the controller simply replied, “Roger,” with no readback to indicate that he had understood the contents of the message. In fact, the comment from Kunovic had failed to stir him from his misguided belief that flight 1308 was already leaving AJO on the 247-degree radial.
Two minutes later, as flight 1308 completed the outbound leg of the holding pattern and began to turn left, Kunovic called to report, “Rolling inbound, out of 6,000.”
The use of the word “rolling,” while not uncommon in Yugoslavia, confused the French controller, who was used to the word “turning.” “Roger, 1308,” he replied, “report turning inbound.” Critically, neither Kunovic nor the controller specified inbound to where.
Kunovic immediately answered, “Turning inbound to Ajaccio because right now we are in cloud.” This still didn’t clarify the situation: Kunovic meant they were turning inbound to the Ajaccio VOR, while the controller thought he meant they were turning inbound to Ajaccio Airport.
As a result, the controller said, “Roger, 1308, report Charlie Tango on final, surface wind two eight zero degrees, twenty knots.” There was no reply from the pilots, who were trying to figure out where Charlie Tango was and why the controller wanted them to report passing it.
Suddenly, as flight 1308 descended toward 4,500 feet amid dense clouds, the ground proximity warning system began to blare: “TERRAIN, TERRAIN, TERRAIN!”
At exactly the same moment, the controller radioed the flight: “1308, it will be as you want, a left-hand circuit runway 21 or right-hand circuit.” The warning and the transmission overlapped to create a startling and confusing flood of disjointed words and noises. For several seconds, neither pilot took any action, as they tried to figure out what was going on and whether the warning was real. The ground proximity warning system increased its urgency: “PULL UP,” it exclaimed, “PULL UP!”
Finally, Captain Kunovic seemed to wake from his startled stupor. “Power!” he shouted. Terglav pushed the throttles forward and began to pull up to climb, but it was too late. As the plane rolled through a 30-degree left turn, the left wingtip of the MD-82 struck a barren saddle near the top of Mont San-Pietro. The impact tore off the outermost 8.5 meters of the wing, filling the cockpit with the terrible sound of rending metal. The plane began to turn over onto its roof as the pilots fought hopelessly for control, flying on for a further seven seconds before plowing headlong into a rock outcrop on the side of a ravine 700 meters below. The brutal collision shattered the MD-82 into millions of pieces, sending chunks of both plane and people tumbling down the sheer face of the mountain. The force of the crash was far beyond the limits of human survival; of the 180 people on board, everyone died instantly on impact.
In the Ajaccio control tower, the controller heard a 4-second transmission from flight 1308 that contained only an eerie whistling sound. With growing apprehension in his voice, the controller asked, “JP 1308, your position?” But there was no reply.
“JP 1308, your position?”
“1308, your position please?”
“JP 1308, your position?”
Concern began to turn to fear. “1308, your position please!” the controller pleaded.
“1308, your position!”
“1308, Ajaccio approach, what is your present position?”
“JP 1308, Ajaccio approach!”
But no matter how many times he called, there was no answer. The controller reported the plane missing and a search and rescue operation kicked into gear, initially scouring the sea off the coast of Ajaccio where the controller thought the plane was last located. However, nothing was found. It was not until 1:40 p.m., nearly five hours after the plane disappeared, that two helicopter crews and a ground team investigating reports of a crash near the village of Petreto-Bicchisano discovered the wreckage high on the side of Mont San-Pietro. The debris had been scattered over an area 600 meters wide and one kilometer long, stretching from the saddle down the steep ravine toward the village. The only recognizable piece of debris was a large section of the fuselage skin, complete with several windows, lodged in the top of the rock outcrop. It was immediately clear that none of the 180 passengers and crew could have survived.
The crash of flight 1308 shocked both France and Slovenia. It was (and still is) both the second deadliest plane crash on French soil, and the deadliest involving a Yugoslav airliner. In Slovenia, home to all 180 victims, the populace was left reeling; it seemed like everyone knew someone who had been on the plane.
The BEA, France’s air crash investigation agency, quickly sent a team to Corsica, accompanied by representatives from Yugoslavia and the United States. Simply reaching the crash site proved difficult, and the investigators knew they would not have the luxury of bringing back all the wreckage for examination. While recovery crews removed the bodies of the victims, the BEA took away little else, save for the black boxes and the few surviving cockpit instruments. The main question they hoped to answer was why the crew descended toward 3,000 feet in a holding pattern where 6,800 feet was the minimum safe altitude.
A careful review of the air traffic control and cockpit voice recorder transcripts revealed that a complex series of misunderstandings had occurred which led the controller to clear the flight to descend below the minimum safe altitude. Interviews with the controller, a 24-year-old new hire who had just received his certificate to serve as approach controller at Ajaccio the previous month, confirmed that he mistakenly thought flight 1308 was on the 247-degree radial when he authorized it to descend. His failure to explicitly clear flight 1308 for the approach caused a divergence in the expectations of the pilots and the controller. Over the subsequent exchanges, each party provided responses that the other was not expecting, causing misinterpretations while attempting to fit them in with their existing models of the situation. Confirmation bias caused the controller to subconsciously place greater weight on statements which seemed to support his assumption that flight 1308 was planning to pass straight through AJO onto the 247-degree radial. Similarly, Captain Kunovic’s periodic references to the holding pattern were discounted because they did not support this pre-conceived picture of the situation.. Imprecise terminology made this possible: phrases like “it will be” instead of “you are cleared” and the use of “inbound” without specifying inbound to where left too much room for interpretation.
The BEA noted that under French air traffic control rules, it was the responsibility of the flight crew to remain above the minimum safe altitude unless the flight was under radar guidance. Because Ajaccio-Campo dell’Oro Airport did not have radar, flight 1308 could not possibly have been receiving radar guidance. In such a situation, controllers were legally allowed to clear flights to any altitude, even below the minimum safe altitude (MSA), since the MSA may change rapidly near the airport and the controller cannot know the exact position of the airplane at the time of the clearance. However, for this system to work, either crews must know when they’re under radar guidance, or they have to be taught to obey published minimums over any air traffic control instruction. In Yugoslavia, controllers typically knew the MSAs well and refrained from issuing any clearances that would violate them; crews expected that they could comply with all clearances immediately without having to check them against a local MSA. In contrast, when controllers at Ajaccio were asked about the MSAs in the area, few could specify them. Furthermore, it is thought that the crew of flight 1308 were not aware that Ajaccio Airport lacked radar. The expectation that they would reject an ATC clearance that violated the MSA was therefore unrealistic.
There was also no evidence to suggest that the crew knew the MSA prior to initiating their final descent. Because of the presence of the copilot’s son on the flight deck, the pilots found themselves repeatedly distracted, and they missed this point during their approach briefing. Even if they did check the local MSA after being cleared to 3,000 feet, the way the approach chart depicted the holding pattern relative to Mont San-Pietro could have led them to believe that it was safe to comply with the clearance regardless of the published minimum. And on top of that, Inex-Adria’s flight operations manual provided contradictory information about what to do when a controller issues a clearance that violates the MSA. The manual stated that upon receiving a clearance, the pilot not flying should immediately program the autopilot to fly to the cleared altitude; however, just a few pages later, it stated that the crew must verify at all times that the flight is not conducted below the MSA, with no exceptions. It did not explain what to do if these two directives conflicted.
All of these findings pointed to a major gray area in French approach procedures that left foreign flight crews particularly vulnerable to errors. But this problem was not unique to France. Although the BEA never mentioned it in its report, the earlier crash of TWA flight 514 bore several striking similarities to the Inex-Adria crash that occurred exactly seven years later. On the first of December 1974, a TWA Boeing 727 on approach to Dulles Airport near Washington, D.C. descended below the minimum safe altitude and collided with Mount Weather, Virginia, killing all 92 people on board. The pilots had been taught to believe that when the controller used the words “cleared for approach,” they were supposed to descend straight to the “approach altitude,” or the MSA at the final approach fix (the last waypoint before the runway). However, at that time they were still more than 60 kilometers from the final approach fix, where the MSA was much higher. They also believed that because Dulles Airport had radar, they would be provided with radar guidance and the controller would keep them away from high terrain. However, both of these assumptions were wrong. Controllers were not taught that “cleared for approach” meant “descend to the altitude of the final approach fix,” and they also were allowed to provide radar guidance at their discretion, a fact which most pilots didn’t know, and the controller was not tracking flight 514’s altitude on radar at the time of the crash. The result of this misunderstanding was that both the pilots and the controller thought the other was making sure that the flight kept away from terrain. One of the main lessons drawn from that crash was that there needed to be a standard lexicon of terms with specific meanings that were common to both pilots and air traffic controllers. The FAA created just such a lexicon the following year, but neither France nor Yugoslavia had followed suit by 1981. Had they done so, the crash of flight 1308 might have been prevented.
The BEA stated in its final report that the probable cause of the crash was the decision by the crew to descend below the MSA, with the misunderstanding between the pilots and the controller among the contributing factors. However, in their addendum to the report, Yugoslav investigators wrote that this should be elevated to the level of probable cause alongside the violation of the MSA, given all the factors which compelled the crew to believe that they could comply with the clearance. They also felt that while the captain did use non-standard terminology, the controller still should have caught on to the fact that flight 1308 was entering the holding pattern, considering that Kunovic explicitly stated what he was doing.
Several other relevant parties were also asked for comment, including Ajaccio air traffic controllers, controllers from Yugoslavia, and pilots’ unions in both countries. Although each had their own opinions about which causes of the crash were most important, many of them asked a similar question: wouldn’t it be better if the holding pattern was over the sea, instead of over the mountains? French aviation authorities must have decided that they had a point. Today, the approach to Ajaccio stays almost entirely over the water and doesn’t go anywhere near Mont San-Pietro.
In its report, the BEA also listed several recommendations of its own. These included that a standard lexicon for pilots and controllers be developed as soon as possible; that crews be taught not to assume that ATC clearances take into account minimum safe altitudes; that controllers receive training on the working conditions of flight crews approaching their airports; that the recording quality of cockpit voice recorders be improved; that radar be installed at Ajaccio Airport; that the Ajaccio approach pattern be revised to keep planes away from high terrain; and that approach charts depict holding patterns in a shape corresponding to the maximum allowable speed therein. Today, most of these recommendations have either been implemented or rendered obsolete. Most importantly, lexicons are now fully standardized throughout the world, which greatly improves the quality of communication between pilots and controllers whose first language is not English.
After all the victims were laid to rest, the investigation concluded, and the recommendations sent to the authorities, one notable task remained: the removal of the debris from atop Mont San-Pietro. Although most plane crashes are cleaned up relatively quickly, this was not the case for Inex-Adria flight 1308. The crash site could only be reached on foot (with difficulty) or by rappelling out of a helicopter, and there was no way to bring heavy machinery anywhere near it. As a result, the vast majority of the wreckage was left in and around the ravine on the north face of the mountain where it ended up after the crash. Over the years, relatives of the victims occasionally visited the area to pay their respects, but otherwise the site was left alone. Weathering slowly reduced the visibility of the fragments; the large section of fuselage skin eventually fell from its perch into the bottom of the ravine, and some pieces began to be absorbed into the tree trunks against which they came to rest.
Then, in 2007, a Slovenian TV station visited the site and broadcast images of the debris still left on the mountainside. As a result of this coverage, Adria Airways (formerly Inex-Adria Aviopromet) and the Kompas travel agency teamed up with the government of Slovenia and local authorities in Corsica to clean up the wreckage. In the summer of 2008, a difficult salvage operation was conducted over a period of two weeks, eventually removing 27 metric tons of debris from Mont San-Pietro by helicopter, including large chunks of the fuselage and a sizeable section of the left wing which was found atop the saddle. The operation also turned up numerous fragmented human remains which were missed during the initial recovery mission in 1981. Thanks to the dedication of the cleanup crew, after 27 long years the last of the passengers — who thought they were going to Corsica for a single day — finally went home.
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