God Grant Forgiveness: The story of the Charkhi Dadri Midair Collision
Note: this accident was previously featured in episode 33 of the plane crash series on April 21st, 2018, prior to the series’ arrival on Medium. This article is written without reference to and supersedes the original.
On the 12th of November 1996, the deadliest midair collision in history lit up the skies outside Delhi, India, as a Kazakhstan Airlines Ilyushin Il-76 plowed into a fully loaded Saudi Arabian Airlines Boeing 747, bringing down both airliners in a hail of debris over the municipality of Charkhi Dadri. By the time emergency services reached the darkened fields where the planes fell to earth, 349 people were dead in what had proved to be India’s worst air disaster. And somewhere amid that vast expanse of burning wreckage lay the clues which would explain how and why the two planes came together. Those clues would lay bare both the inadequacy of India’s aviation infrastructure and the lingering failure of post-Soviet airlines to integrate into the global aviation system. It was the convergence of these two systemic failures, coming together in an escalating web of misunderstandings aboard the Kazakh airliner, which led to one of the worst plane crashes of all time — a catastrophe whose immense scale belied its almost trivial preventability, and whose causes are still poorly understood, despite the official inquiry’s half-hearted attempts to clarify them.
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For the airlines of the former Soviet Union, the 1990s were a time of immense hardship, marked by financial insolvency, operational difficulties, poor management, and dismal market prospects. This was no less true in the newly independent Central Asian nation of Kazakhstan than it was in Russia. Kazakhstan’s air travel market was tiny, barely big enough for the state-owned flag carrier Kazakhstan Airlines, which had split off from the once mighty Aeroflot during the Soviet breakup. The airline was never really solvent, and Kazakhstan has gone through two more flag carriers since, finally settling on Air Astana in 2004, following the failure of both Kazakhstan Airlines and its successor Air Kazakhstan. Indeed, by November of 1996, just short of five years on from Kazakhstan’s independence, its national airline was teetering on the brink of bankruptcy, and in fact it was just days away from being shut down — a demise which was no doubt hastened by the events to come.
One popular way for struggling post-Soviet airlines to make money was by offering merchant charters, an unusual service which predominantly arose in Russia and Central Asia. One of the few reliable ways to earn cash in that region during the upheaval of the 1990s was by reselling foreign goods to make up for the massive domestic shortfalls created by the collapse of the USSR’s industrial sector. Many former Aeroflot subsidiaries took advantage of this phenomenon by offering charter flights to groups of merchants, who would fly abroad on a mostly empty plane, then fill it with purchased goods on the return flight.
Many, perhaps even most, of these merchant charters used the Soviet-built Ilyushin Il-76, a hulking, four engine multi-purpose transport which bore some passing resemblance to the C-141 Starlifter. First conceived in 1967 as a military cargo plane, the Il-76 was designed to take off and land on unimproved airstrips while carrying large payloads from one side of the Soviet Union to the other. It featured a high-wing, T-tail design, ideal for short takeoffs on dirt runways; a large cargo compartment which could be fitted with passenger seats; a rear ramp capable of opening in flight to deploy paratroopers or airdrop supplies; a hermetically divided interior to allow separate depressurization of the cockpit and cabin; and a split double-decker cockpit, with two pilots, a flight engineer, and a radio operator on the upper deck, and a navigator on the lower deck, which featured its own set of inverted cockpit windows, giving the aircraft’s nose section a highly distinctive appearance. Although it was primarily designed as a military transport, capable of interchangeably carrying either military vehicles or whole contingents of paratroopers, it also found use with Aeroflot as a civilian cargo plane. Following the breakup of Aeroflot, many Il-76s subsequently found their way into the newly independent airlines, which used them for both cargo and passenger flights, sometimes simultaneously.
Flying as a commercial passenger aboard an Il-76 was an odd experience, given the lack of a traditional cabin — after all, the passenger seats and amenities were installed directly into the cargo bay. However, this setup was ideal for the merchant charters because it allowed the carriage of both bulk goods and the merchants themselves using a single aircraft, which saved time, money, and resources.
In November 1996, Kazakhstan Airlines concluded just such a charter arrangement with a company from neighboring Kyrgyzstan, which wanted to send 27 traders to India to buy cheap textiles for resale in Central Asia. In turn, Kazakhstan Airlines provided an Il-76, registered as UN-76435, which was at that time still fairly new, having rolled off the assembly line in 1992, after the breakup of the Soviet Union. The charter flight, designated flight 1907, was to leave Shymkent, Kazakhstan, on November 12th, fly to Delhi, India, and then reverse that journey once the passengers had purchased enough textiles to fill the plane.
On the afternoon of the appointed date, flight 1907 departed Shymkent with 37 people on board, including the 27 merchants, five cockpit crew, and five other crewmembers, presumably flight attendants and cargo handlers. In the upper cockpit sat 44-year-old Captain Alexander Robertovich Cherapanov, 37-year-old First Officer Ermek Kozhahmetovich Dzhangirov, 50-year-old Flight Engineer Alexander Alexandrovich Chuprov, and 41-year-old Radio Operator Egor Alekseevich Repp, while 51-year-old Navigator Zhahanbek Duisenovich Aripbaev occupied the lower deck. All were veteran pilots, and even the least experienced crewmember — First Officer Dzhangirov — had over 6,000 flying hours.
The flight from Shymkent to Delhi is not a particularly long one, lasting just three hours and ten minutes. The pilots first made contact with Delhi only 35 minutes after takeoff, and checked in again several times after that, reporting that all was normal in cruise at 33,000 feet.
The flight, however, was not quite direct, due to a quirk of the airspace rules around Delhi at that time. In India in 1996, there was no unified structure for military and civilian airspace and air traffic control. Military and civilian controllers did not talk to one another, did not handle each other’s aircraft, and did not have joint jurisdiction over any airspace; instead, the skies over India were divided roughly 50–50 between civilian and military control, with civilian aircraft barred from military airspace and vice versa, unless necessitated by circumstance.
Up until 1995, when it was transferred to the Airports Authority of India, Delhi’s Indira Gandhi International Airport had been run by the Indian Air Force, and the majority of the airspace around it was under military rather than civilian control. In fact, only one air corridor into and out of Delhi was open to civilian traffic — a situation which would constitute one of the first links in the chain of events leading to the coming catastrophe.
An air corridor or airway is a designated path between two points which is used by aircraft while en route, prior to beginning the approach sequence or after completing the standard departure procedure. While civilian aircraft were free to maneuver in the area immediately around Indira Gandhi International Airport, allowing them to land on any runway, the only way for inbound flights to get near the airport in the first place was to take up an air corridor called Route G452, which ran due west from the airport to a point called LUNKA, 177 nautical miles west of Delhi. Furthermore, after takeoff, departing aircraft were required to take up this same air corridor. Flight in any other direction was prohibited, as it would violate the exclusive military airspace surrounding the city.
At 18:23 local time, flight 1907 reported passing LUNKA, and five minutes later it received clearance to descend to 20,000 feet. This clearance was subsequently extended to 18,000 feet at 18:33, and the Radio Operator Egor Repp acknowledged the instruction.
At that exact same moment, a Saudi Arabian Airlines Boeing 747–100 lifted off the runway at Indira Gandhi, operating flight 763 with service to the city of Dhahran on Saudi Arabia’s eastern coast. On board were 289 passengers, mostly Indian laborers and hospitality workers headed for jobs in the Gulf, along with some Muslim pilgrims connecting through Dhahran on their way to Mecca. The flight also featured 23 crewmembers, including a three-member flight crew consisting of Captain Khalid al-Shubaily, First Officer Nazir Khan, and Flight Engineer Ahmed Edrees.
After takeoff, the pilots contacted the Delhi approach controller, who was responsible for both arrivals and departures, and received clearance to climb to 10,000 feet along Route G452, the same air corridor along which Kazakhstan Airlines flight 1907 was currently descending. Due to the fact that only one air corridor was available for both inbound and outbound aircraft, it was standard procedure at Delhi to funnel the departures underneath the arrivals, and it was the approach controller’s intention to do the same for the Saudi and Kazakh jets.
At 18:35, Radio Operator Repp aboard the Kazakh Il-76 called air traffic control and said, “Good evening, one nine zero seven. Passing through two three zero for one eight zero, seven four miles from DPN [Delhi].”
“Descend one five zero, report reaching,” the controller replied, clearing the flight down to flight level 150, or 15,000 feet.
“One five zero,” Repp acknowledged.
Over the internal radio, Navigator Aripbaev reported, in Russian, that 15,000 feet was equal to 4,570 meters. Like all Soviet-built airplanes, the Il-76 was originally designed as a fully metric aircraft, so it came with altimeters demarcated in meters rather than feet. This particular aircraft, having been built after the fall of the Soviet Union, was fitted with what may have been aftermarket altimeters demarcated in feet, but there were only two of them — one for the captain and one for the navigator — and none for First Officer Dzhangirov, who was the one actually flying the plane. Radio Operator Repp, who was the only crewmember talking to air traffic control, had no altimeters at all, metric or otherwise.
One minute later, Saudi Arabian Airlines flight 763 called the controller and reported that they were “approaching [flight level] 100,” or 10,000 feet, at which point the controller cleared them to climb to 14,000. The scenario was now set: Kazakhstan Airlines flight 1907, flying no lower than 15,000 feet, would pass no less than 1,000 feet over the top of Saudi Arabian Airlines flight 763, the standard minimum vertical separation prescribed by international regulations.
At 18:37, Repp again asked Navigator Aripbaev to confirm that 15,000 feet was equal to 4,570 meters, which he did, but there was no specific acknowledgement of this fact by the pilots.
Just before 18:39, Saudi Arabian Airlines flight 763 reported “approach level 140 for higher.” But instead of giving them a new clearance, the controller said, “Maintain level 140, standby for higher,” forcing flight 763 to level off to allow the Kazakh Il-76 to pass overhead.
Seconds later, the controller called the Il-76 and said, “KZN one nine zero seven, report distance from DPN,” referring to the beacon at Indira Gandhi International Airport.
“Now reached flight level one five zero, four six miles from Delta Papa November, radial two seven zero,” Repp replied, reporting their altitude and location.
Despite the fact that he reported having reached 15,000 feet, the Il-76 was actually still at approximately 16,400 feet at that time. The reason for this discrepancy is unclear, but it’s possible that Repp was simply guessing their altitude, since he would have had to peer around in a rather uncomfortable manner to read either pilot’s altimeter. Alternatively, he might not have understood the difference between “reached” and “approaching.” In any case, however, the controller replied, “Roger, maintain flight level one five zero. Identified traffic twelve o-clock, reciprocal, Saudia Boeing 747 at ten miles, likely to cross in another five miles. Report if in sight.”
Repp took a long time to reply to this message, during which time Captain Cherepanov and First Officer Dzhangirov could be heard discussing the traffic in the background. Finally, after a lengthy pause, Repp asked, “Kazakh one nine zero seven, report how many miles?”
“Traffic is at eight miles, level one four zero,” the controller repeated.
Having received the clarification he needed, Repp said, “Now looking, one nine zero seven.” This would be the last transmission from the Kazakh jet.
At that moment, flight 1907 reached 15,000 feet and, mysteriously, kept descending. The crew should have known that they were not cleared to descend below this altitude, but for nearly 30 seconds, no one said a word as the altimeters unspooled toward 14,000 feet. Simultaneously, the flight entered a large, fluffy cumulus cloud, disappearing into a towering wall of white.
Suddenly, at 18:40, someone, probably Radio Operator Repp, called out, “Hold the level!” He must have finally gotten a good look at an altimeter and realized they were too low.
But instead of leveling off immediately, Captain Cherepanov hesitated, then asked, “What level were we given?”
How could it be that after all the discussions between Repp and the controller, the Captain didn’t know that they were supposed to level off at 15,000 feet?
Adding to the confusion, Flight Engineer Chuprov then called out, “maintain,” without saying what level they were supposed to be maintaining.
But Repp at least knew what he was talking about. “Keep to level one fifty, don’t descend!” he yelled.
Realizing that he had made a mistake, Captain Cherepanov immediately disconnected the autopilot and ordered Flight Engineer Chuprov to increase engine power.
As the engines spooled up with a high-pitched whine, the cockpit voice recorder captured Repp shouting, “Get to one fifty because on the one forty — THAT ONE!”
At that moment he must have caught a fleeting glimpse of the Saudi jet headed straight for them through the clouds, but there was no time to react. With a horrific crunch, the Il-76 slammed headlong into the 747 with enormous force. The Boeing’s two left engines collided with the left wing of the oncoming Il-76, triggering a massive explosion, followed a split second later by a secondary collision as the 747’s left horizontal stabilizer cut clean through the Il-76’s vertical tail. For a moment the two planes continued forward, suspended within a tremendous fireball, before they each began to turn over into mirrored death dives, spiraling down from 14,000 feet as debris fell like rain behind them.
In the Delhi approach control center, controller V. K. Dutta watched as the targets of the two aircraft merged on his radar screen, failed to separate, and then disappeared altogether. Seconds later, his radio crackled to life, and he heard a voice screaming in Arabic, “Astaghfor Allah, ashhau unlealaha ella Allah” — “God grant forgiveness, I witness no other god but Allah!” It could only have been Saudi Arabian Airlines flight 763, but after that, no more was heard. With deepening horror, he called both the Saudi and Kazakh jets over and over, never to receive a reply.
Cruising at 20,000 feet some miles distant, the pilot of a US Air Force plane saw a cloud light up in flickering orange, and then two flaming objects emerged from beneath it, falling in long descending arcs toward the ground. In a semirural area west of Delhi, additional witnesses caught sight of the Saudi 747 in a steep, inverted dive, its burning tail section disintegrating behind it. Two villages over, others saw the Kazakh Il-76 falling like a leaf, spinning about the fiery gap where its left wing used to be. Finally, one minute after the collision, both planes struck the ground, sending up twin columns of black smoke against the reddened sunset.
Pushing their way through narrow streets and rutted rural lanes, emergency services hurried to the scene of the disaster, in the countryside near Charkhi Dadri, some 75 kilometers west of Indira Gandhi International Airport. By the time they got there, thousands of people were already at the crash sites, searching for survivors. The scene which they encountered was positively apocalyptic. Wreckage, some of it on fire, was strewn thickly over an area some seven kilometers long, with the 747 at one end and the Il-76 at the other. The 747 had impacted nose-first at a high rate of speed, carving out an enormous crater in a fallow field near the village of Dhani Phogat, where blackened debris, hardly recognizable as that of an airplane, lay like a heap of burning trash just meters from a densely populated neighborhood. All around were bodies and pieces of bodies, some of which had been blasted back out of the crater, while others were ejected from the plane in flight as the tail section broke apart. Additional pieces of the tail and engines from the 747 had come to rest up to four kilometers away, near the start of the wreckage trail of the Il-76.
The remains of the Il-76 were distributed over an area four kilometers square between the villages of Birohar and Khachroli, with pieces of the left wing and horizontal stabilizer closer to the beginning, and the fuselage near the end. Unlike the Saudi jet, the Il-76 had impacted the ground in a nearly flat attitude, with its forward fuselage including the cockpit lying on its side in a field, remarkably intact, some distance away from the center and rear sections, which were almost totally consumed by fire.
In the initial confusion, first responders were told that three or four people may have survived, but the reports proved false, as rescuers failed to find anyone alive at either crash site. Media in turn were given the reports of survivors, and journalists hurried to hospitals in the Delhi area, only to find that no one had been admitted. Indeed, by the time dawn broke over the ruined fields of Charkhi Dadri, it was clear that all 312 passengers and crew aboard the Saudi 747 and all 37 aboard the Kazakh Il-76 had perished in the crash. With 349 people dead, that made the collision over Charkhi Dadri the worst air disaster in India, the deadliest mid-air collision in history, and the third deadliest plane crash of all time — all titles which it still holds today.
The unprecedented catastrophe shocked the world and further undermined confidence in India’s already poor aviation safety record. Recriminations began to fly immediately, as Indian, Kazakh, and Saudi officials traded accusations about who was to blame. Many articles were written about the poor state of aviation infrastructure in India and the poor English language skills of ex-Soviet pilots. But what was the truth? Who hit whom, and why? Could it have been prevented? Answering those questions would fall to a specially appointed Board of Inquiry, led by the Honorable Justice R. C. Lahoti of the High Court of Delhi. But while his inquiry did produce some basic answers, as the following analysis will show, there was much that Justice Lahoti left unexplored and unexplained.
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The most important question was which plane, if either, was not where it was supposed to be. From the air traffic control recordings, it was obvious enough that controller V. K. Dutta was not at a fault — he had told the Kazakh plane to level off at 15,000, and the Saudi plane to level off at 14,000, in accordance with standard procedures. Therefore, for the two planes to have collided, one or both must have deviated from its assigned altitude. To find out which one, investigators needed to decipher the contents of the black boxes, which proved to be a rather messy affair, as disputes arose over where and by whom the recorders should be opened.
In the end, the 747’s flight recorders were analyzed by the British Air Accidents Investigation Branch in Farnborough, UK, while the recorders from the Il-76 were taken to an Interstate Aviation Committee (MAK) facility in Moscow. The two third party agencies downloaded and analyzed the flight recorder data, and both independently determined that the collision took place at 14,000 feet. There was no evidence that the Saudi jet had ever strayed from its assigned altitude before the Kazakh jet plowed into it. So why didn’t Kazakhstan Airlines flight 1907 level off at 15,000 feet as it had been ordered to do?
Representatives of Kazakhstan Airlines put forward a far-fetched argument that severe turbulence had caused the Il-76 to fall 1,000 feet below its assigned altitude. In support of their proposal, they cited the fact that the Il-76’s flight recorder data did not show a continuous descent from 15,000 to 14,000 feet, but rather two sudden jumps after distinct periods of level flight. Taken at face value, the data appeared to show the Il-76 leveling off for eleven seconds at 14,900 feet, dropping 400 feet in half a second, leveling out once more at 14,500 feet, then dropping several hundred feet again before leveling out a third time just before the collision.
This argument was, however, easily dismissed. Although the planes were flying in cloud at the time of the collision, and some minor turbulence was evident on the Il-76’s flight data recorder, there were no storms or other adverse weather in the area, and none of the pilots commented on the presence of any severe turbulence. And besides, a plane cannot go from level flight, lose 400 feet, and then level out again in less than a second — the airframe will break apart. In the opinion of the MAK experts in Moscow, these abrupt jumps were the result of a “sticky” sensor which continued to report the same altitude over and over again before suddenly updating. A performance study by the AAIB further concluded that the Il-76 was probably in a continuous descent all the way down to 14,000 feet, at which point it might have just begun to level out before it slammed into the unsuspecting 747.
To understand why the crew of the Il-76 failed to level off at 15,000 feet, the investigators focused on the conversations between the five cockpit crewmembers and between the Radio Operator and air traffic control.
The avenues of communication aboard the Il-76 were complex. Neither of the pilots spoke directly to air traffic control, so ATC instructions had to be relayed to them via the Radio Operator. But the Radio Operator didn’t have his own altimeter and appeared at times to be unsure of their altitude. Furthermore, altitude callouts were the responsibility of the Navigator, who wasn’t even in the same room, and at no point during the descent did he make any such callouts anyway.
And then there was the matter of language. All the internal cockpit conversations took place in Russian, but the exchanges with ATC were in English. There was consequently considerable debate about how well the pilots spoke English and whether they could have misinterpreted the controller’s instructions.
According to the Board of Inquiry, it was this latter issue which was the most important factor in the pilots’ failure to level off at their assigned altitude. In their opinion, when the controller told flight 1907 to level off at 15,000 feet, the Radio Operator and Navigator’s back-and-forth conversation in Russian about the conversion of this altitude to meters meant that the other pilots should have been aware of their assigned altitude. However, when the controller subsequently told them to watch for the 747 ahead of them at 14,000 feet, the length of time taken for Radio Operator Egor Repp to respond indicated two things: first, that he was having difficulty understanding the instructions in English; and second, that neither he nor any other crewmember had understood the controller’s earlier instructions to the Saudi jet — which were broadcast on the same frequency — because if they had, they would have anticipated the subsequent traffic notification and should not have been surprised by its contents. The Board proposed that, having missed this key context, First Officer Dzhangirov and Captain Cherepanov heard the controller say “Traffic is at eight miles, level one four zero,” and interpreted this as a statement of the traffic’s location followed by a new cleared altitude, when in fact “level one four zero” was part of the traffic information. In short, because of their poor understanding of English, they thought the altitude of the Saudi aircraft was meant for them, and consequently flew right into it.
However, this theory, while plausible, is incomplete. In fact, the Board presented very little evidence to support it, and failed to rule out a number of alternative lines of inquiry.
First of all, it is not clear from the evidence presented in the Board’s report whether Captain Cherepanov and First Officer Dzhangirov spoke English or not. According to contemporary media reports, Kazakhstan Airlines claimed that all the crewmembers were proficient in English, although there is good reason to doubt this assertion. Most pilots in the Soviet Union did not learn English unless they were part of the elite few assigned to international flights, and just five years after the breakup, the situation had not markedly improved. Comprehension of English among ex-Soviet flight crews was notoriously poor, and as late as the 2010s, MAK investigations into accidents in Russia were finding evidence of widespread falsification of English test results. However, according to media reports, airline officials claimed that First Officer Dzhangirov not only possessed a certificate of English proficiency, but was actually involved in teaching English to other pilots. Given the airline’s shaky relationship with the truth during the inquiry, no one would be surprised if this turned out to be a lie, but the Board of Inquiry didn’t even attempt to find out. The final report explicitly states that no Indian investigators traveled to Kazakhstan to inspect the airline’s operations, nor were any witnesses called to testify about them. Without any verification of the authenticity of First Officer Dzhangirov’s certificate of English proficiency, it cannot be ruled out that he actually did understand English, and therefore should have been able to interpret the controller’s instructions correctly.
In fact, while cockpit conversations were entirely in Russian, and while Radio Operator Repp clearly had some comprehension difficulties, the cockpit voice recording — or at least the parts of it described in the official report — offered no evidence one way or the other concerning the Captain and First Officer’s comprehension of English. In fact, despite the Board’s assertions, there doesn’t appear to be any evidence of either pilot reacting to any air traffic control instruction during the final minutes of the flight, raising the question of whether they were even listening. For one, the Board claims that the pilots were aware that they were cleared initially to 15,000 feet because the Radio Operator and Navigator were talking about it in Russian. But in a five person cockpit, it’s just not the case that something being discussed between two crewmembers will be picked up by the other three, and the available portions of the transcript do not suggest that either pilot ever acknowledged the clearance to 15,000 feet.
Because of the above, it’s difficult to say whether the pilots’ apparent ignorance of various ATC instructions was because they couldn’t understand English, or because they simply weren’t paying attention. Further confounding the situation, however, is the report’s brief reference to a conversation between Cherepanov and Dzhangirov concerning the traffic, which took place during Repp’s attempts to clarify the contents of the traffic notification. The contents of this conversation were not reproduced in the official report, but the fact that it took place suggests that the pilots were paying attention to the traffic notification, or at least understood that a traffic notification had been made.
After considering these complicating factors, it becomes uncertain whether the pilots descended below 15,000 feet because they mistook the altitude of the traffic for their own cleared altitude, or because they never knew what altitude they were cleared to in the first place. In fact, eighteen seconds before the collision, Captain Cherepanov asked “What level were we given,” which obviously represented a shocking lack of situational awareness on his part, but also provided another conflicting clue. The Board of Inquiry interpreted this statement as evidence that he thought they were cleared to flight level 140, only to become confused when Repp told him to “hold the level” prior to reaching it. On the other hand, it could just as easily mean that he never had any idea when they were supposed to level off, and was expecting one of the other crewmembers to take care of it.
This kind of “not my problem” attitude was a major issue affecting Soviet and ex-Soviet flight crews, and arose in part due to the large cockpit crew sizes on many Soviet aircraft. Readers of my earlier article on the crash of Mozambique’s presidential plane, which also featured a five-person Russian cockpit crew, may recall that several of the crewmembers were not doing anything during the flight, and appeared totally disconnected from their colleagues’ actions. We could therefore speculate that Captain Cherepanov wasn’t paying attention to their cleared altitude, while at the same time, First Officer Dzhangirov expected Captain Cherepanov to tell him when to stop the descent.
On top of all of this, we must also consider the possibility that Dzhangirov knew they were supposed to level off at 15,000 feet, but became distracted and simply forgot to do so. This type of error has been seen countless times in controlled flight into terrain type accidents, in which a crew on approach to an airport inadvertently lets their plane descend straight into the ground while searching outside for some sign of the runway. In this case, there is evidence that the pilots were looking outside the plane for the oncoming traffic at around the time they dropped below 15,000 feet. We could speculate, then, that they weren’t looking at their altimeters and did not notice that they had passed their cleared flight level. Speculating further, they might have heard Repp telling ATC that they had “reached 15,000 feet,” then looked at their altimeters, realized that they were still at 16,400 feet, and concluded that they should wait before leveling off, only to lose track of time.
The poor design of the Il-76’s cockpit may have contributed to such a lapse in attention. The fact that the First Officer lacked an altimeter demarcated in feet is obviously worth mentioning, although its connection to the accident, if any, is unclear. The large number of people on the flight deck also made it easy for the non-flying crewmembers to slack off without anyone noticing, and the fact that the Navigator was isolated in a different part of the airplane could have contributed to his casual omission of the required altitude callouts. Furthermore, in the absence of these callouts, the Il-76 did not have any backup system to warn the pilots when they were getting close to their cleared altitude. All Western passenger jets built since at least the 1960s have had an altitude alert system, which produces a chime when approaching a target altitude set by the pilots. The Il-76, however, did not have even this basic feature. Nor did it have another feature common on Western airliners: an altitude capture mode, which allows the autopilot to automatically level the plane upon reaching an altitude previously selected by the crew. Had either of these systems existed on the Il-76, it is doubtful that the accident would have occurred at all.
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All of this having been said, international rules hold that responsibility for prevention of midair collisions lies with both pilots and air traffic controllers. Therefore, one of the questions considered by the Board of Inquiry was whether approach controller V. K. Dutta could have done anything to avert the catastrophe.
As it turned out, however, there was no way Dutta could have known that Kazakhstan Airlines flight 1907 had not complied with his order to level off at 15,000 feet. In fact, he had no way to determine the altitude of any aircraft, because he was working with primary radar only. The most primitive form of the technology, primary radar works by bouncing radio signals off of an object to determine its location and direction of travel, without providing any information about the object’s identity, or its altitude. This type of radar hadn’t been considered state-of-the-art since about 1960. By 1996, any properly equipped ATC facility should have been using secondary surveillance radar, or SSR, which forms a two-way connection with an airplane’s transponder in order to display its identity and altitude in addition to its location and movement.
Without secondary radar, V. K. Dutta did not and could not know whether airplanes were obeying his altitude instructions — he could only trust the responses given to him by the crews under his control. In this case, both crews had told him that they were at their assigned altitudes, so as far as he knew, separation was assured.
The Board of Inquiry obviously could not avoid the question of why Indira Gandhi International Airport still did not have secondary surveillance radar in 1996. As it turned out, plans to upgrade to an SSR system had been in place for at least a decade, but its procurement and installation had gotten bogged down in a sea of government paralysis. The government of India has never been particularly good at getting things done, but in the case of air traffic control infrastructure, it was particularly far behind. Responsibility for air traffic control in fact bounced around between several government agencies during the 1980s and 1990s, until controllers at last found themselves under a subordinate branch of the independent Airports Authority of India, which was not even part of the Directorate General of Civil Aviation (DGCA), and whose structure prevented ATC experts from rising higher than a tertiary management role which didn’t report directly to the chairman. Consequently, ATC improvements were, so to speak, not on anyone’s radar. Despite this, some unsubstantiated news reports claimed that a secondary surveillance radar system had actually been delivered to the airport some time ago, but for unknown reasons, it hadn’t even been unpacked, let alone installed, by the time of the accident.
Adding further insult to injury, it turned out that Indian Air Force controllers in Delhi had active secondary radar covering the area where the accident occurred, even though civilian controllers didn’t, but because of the structure of India’s air traffic control network, they did nothing to prevent the crash. In fact, because of the complete segregation of civilian and military airspace in India, military controllers had no reason to look at the civilian air corridor where the accident occurred, and even if they had, they had no way of contacting their civilian counterparts to warn them of the impending collision.
The airspace segregation was also the reason why the two flights were put on a collision course in the first place. Although the Board of Inquiry emphasized that routing arrivals 1,000 feet over the top of departures was fully in compliance with international standards, they did admit that using multiple unidirectional air corridors to separate departing and arriving aircraft was preferable. In his report, Justice Lahoti nevertheless defended the safety of the airspace around Indira Gandhi, writing that, “Entry and exit of aircraft through a ‘single corridor,’ when under radar control with provision of applicable separation minima, [does] offer adequate safety, provided the aircraft adhere to the ATC clearances.” This is of course a meaningless statement. A proper analysis of the risk posed by such a procedure ought to weigh both the likelihood and consequences of any non-compliance with ATC clearances. Subjectively, it would seem that the risk involved in the single air corridor setup was considerable, since it routinely placed departing and arriving aircraft on a collision course, with flight crew adherence to altitude instructions being the only safeguard against disaster. Justice Lahoti argued that any arrangement could be considered dangerous if crew non-compliance with ATC orders is assumed, but not all types of non-compliance are created equal. Lateral errors are in fact much rarer than vertical errors, which means that in practice, two parallel, unidirectional air corridors carry less collision risk than one bidirectional air corridor.
Despite his fallacious arguments regarding the relative safety of single air corridors, Lahoti did acknowledge that this arrangement could not continue, especially in light of increasing traffic turnover at Indian airports following the liberalization of the airline industry in 1992. He also pointed out that the Board of Inquiry into a 1971 accident in Delhi had recommended that India’s civilian and military air traffic control networks be integrated, but that 25 years later this still hadn’t been done, in large part due to the Air Force’s reluctance to give up its sole authority over 50% of Indian airspace.
In part spurred by the collision over Charkhi Dadri, Indian air traffic controllers went on strike in 1997, protesting against poor working conditions, cramped control towers, antiquated equipment, low pay, and lack of staff to cope with increasing traffic. The strike and the accident contributed to a number of reforms, which included the installation of secondary radar at major airports, the restructuring of ATC within the government bureaucracy, formal licensing of air traffic controllers (there previously was no standard for ATC certification in India!), and the creation of new civilian air corridors around Indira Gandhi International Airport. The Board of Inquiry urged other reforms as well, including the expansion of the DGCA’s accident prevention program, which at that time had just one employee; and the institution of a requirement that only pilots, and not other crewmembers, speak to controllers.
The disaster also drew attention to the need to expand the use of Traffic Collision Avoidance Systems, or TCAS. Still relatively new at the time, TCAS equipment had already revolutionized collision avoidance in the United States, where the systems had been mandatory since 1993. TCAS detects the transponders of nearby airplanes in order to determine whether a collision risk exists, and if it detects that a collision may be imminent, it will automatically instruct the pilots to execute evasive maneuvers. Unfortunately, neither plane involved in the Charkhi Dadri collision was equipped with TCAS. If they had been, the collision most likely would not have occurred. Recognizing this fact, India took bold action, and in 1999 became just the second country in the world to mandate that all aircraft in its airspace be equipped with TCAS.
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In the end, although the Board of Inquiry made substantial recommendations which led to improvements in air safety in India, its final report left plenty of ambiguity about what happened and why. In fact, to a great extent, reliable information about the disaster does not exist. Most online sources of information about the collision contain statements which are directly contradicted by the official report, but the report itself is also internally inconsistent and draws conclusions unsupported by evidence. Although most media are content to repeat the Board’s explanation, I was forced to conclude that we really don’t know why Kazakhstan Airlines flight 1907 descended into the path of Saudi Arabian Airlines flight 763. The cockpit of the Il-76 was in a state of advanced dysfunction which the Board of Inquiry thoroughly failed to elucidate. Although it’s uncertain whether any opportunities for safety improvements were missed as a result of this failure, it was in any case poor investigative practice, and deserves to be criticized for that alone.
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In the years since the conclusion of the inquiry, the Charkhi Dadri midair collision has faded from memory, both in India and abroad, with startling rapidity. It is rare to see it mentioned in the same breath as history’s other deadliest air disasters, most of which occurred much longer ago, but are better remembered. Part of that obscurity can probably be put down to who died — the poorest citizens of an already poor country, many of them on their way to indentured servitude, leaving nothing to their name when they departed. Many of the victims’ bodies were never identified, and some of them came from such deeply poverty-stricken, rural backwaters that their next of kin were never identified either. Somewhere out there, there are almost certainly families who have no idea that their missing brother, sister, son, or daughter died aboard Saudi Arabian Airlines flight 763 — for all they know, their loved one simply went away and never came home.
A different but equally haunting story is that of the Saudi pilots — a crew who did nothing wrong, who were simply doing their jobs, only to end up in the wrong place at the wrong time, struck down so suddenly, as though they had been swatted from the sky by the hand of god. They may or may not have known what hit them, but they had long enough to pray for salvation, not in this world but in the next, for they knew that they were going to die. As for the crew of the Kazakh jet — the collision obliterated their aircraft so thoroughly that they never had a chance to leave a record of their final thoughts, but their fate was no doubt equally horrible, to say nothing of their passengers. But in the end, they probably did not have time to contemplate the banality of the disaster. It was such a simple mistake that did them in, and such a sad and bloody legacy that it left behind.
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