Missing the Point: The crash of Air China flight 129

The wreckage of Air China flight 129 sits atop Mount Dotdae after the crash. Image source: Mayday

On the 15th of April 2002, Air China flight 129 was on approach to Busan, South Korea when its pilots began to lose the plot. They switched to another approach at the last moment, transferred command just minutes from landing, missed briefings, flew off course in fog, and pressed onward in a futile search for the runway. Just a few kilometers short of the airport, the crew suddenly found themselves flying straight at a descending ridge of Mount Dotdae. Despite the captain’s last-ditch attempt to climb, the Boeing 767 crashed into the forested ridge, catapulting flaming wreckage over the summit and down the other side. Inside the ruined plane, survivors fled for their lives as fire tore through the cabin, killing those who could not escape. Of the 166 people on board, only 37 survived — including the captain, who insisted that everything was fine up until the moment of the crash. But investigators found that in reality, a long string of poor decisions and unfortunate coincidences had put flight 129 on a collision course with the mountain — findings which raised doubts about the quality of Air China’s training regime and triggered an international argument over who was to blame.

The Boeing 767 involved in the accident. Image source: Alain Durand

Air China flight 129 was a regularly scheduled flight from Beijing to Busan, South Korea, with China’s state run international air carrier. In command of the 17-year-old Boeing 767 that day were Captain Wu Xinlu, age 30, and First Officer Gao Lijie, age 29; also in the cockpit was another first officer, 27-year-old Hou Xiangning, who was acting as second officer (in charge of radio communications only) to gain experience with the approach procedures for Busan. Eight flight attendants also boarded the plane to care for the 155 passengers, making for a total of 166 people on board. They should have been in good hands: since its creation in 1988, Air China had never had a fatal accident.

At 8:37 a.m. local time, flight 129 left Beijing, running 17 minutes late. First Officer Gao was designated as the pilot flying, while Captain Wu monitored the instruments and Second Officer Hou handled the radio calls. Their plan was relatively simple: upon nearing Busan’s Gimhae Airport, they would line up with runway 36L from the south and perform a straight in approach with the help of the instrument landing system (ILS). On the occasions when Wu and Gao previously flew to Busan, this was the approach they had used.

Weather conditions in Busan that day were poor. During late spring and summer, southerly winds blowing from over the sea create low clouds and drizzle that blanket South Korea’s southern coast. On the day of flight 129, just such a cloud bank had smothered the city down to a low altitude, accompanied by rain and a stiff south wind. As Air China flight 129 neared Gimhae Airport, the approach controller observed that planes landing on runway 36L would be dealing with a significant tailwind. It is always safer to land into the wind because less stopping distance is needed after touchdown. Therefore, the approach controller changed the active runway to runway 18R — the same runway from the other direction. Instead of doing a straight-in ILS approach to runway 36L as planned, the controller instructed flight 129 to perform a circling approach to runway 18R. In a circling approach, the crew descends toward the runway using the ILS until the airport is in sight; then, while maintaining visual contact with the runway, they loop around the airport and land from the other direction. If the pilots lose sight of the runway at any point during the loop, they must make an immediate missed approach, climbing out to try again.

A straight-in approach to runway 36L vs. a circling approach to runway 18R. Map source: Google

None of the pilots of flight 129 had performed a circling approach at Gimhae Airport before. The change of plans also came at the last moment, leaving them little time to prepare. Before the flight, and again before the descent, they had conducted an approach briefing for a straight-in approach to runway 36L — now all that preparation had to go out the window. Instead of running through a full briefing for the new approach, First Officer Gao gave an abbreviated version that missed key points and focused mainly on where they would taxi after landing. When it came to maneuvering around the airport to line up with the new runway, the pilots would be effectively winging it.

From the moment that the approach plan changed, the workload in the cockpit increased rapidly. With limited time and numerous tasks demanding their attention, the pilots started to miss things. As the plane entered an area of rain, Captain Wu said, “It’s raining, we didn’t receive any information on rain?” And yet, just minutes earlier, they had heard a weather broadcast that mentioned the presence of rain. In fact, the visibility at that moment was below the minimum for landing a wide body jet at Gimhae, but neither the pilots nor the controller knew this.

Wind began to buffet the flight, prompting First Officer Gao to exclaim, “The wind is so strong!” It would be the first of several comments in which he expressed his difficulty flying the plane.

The path of flight 129, overlaid with the correct approach pattern and the CVR transcript. Map source: Google

At 11:17 a.m., the controller cleared flight 129 to begin the circling approach as soon as they had the airport in sight. First they would turn left, then turn back to the right paralleling the runway, a stretch referred to as the “downwind leg.” Then they would turn 180 degrees to the right, a move called the “base turn,” in order to line up with the runway. After catching sight of the runway at 11:18, Gao disconnected the autopilot, announced “I have control,” and began the initial left turn. But right off the bat, he made an error: instead of turning sharply to the left to get away from the airport, he made a gentler, shallower turn, cutting inside the normal circling approach path. None of the pilots noticed or corrected the mistake, possibly because they hadn’t briefed the approach properly, preventing them from forming an accurate mental model of the route.

Leveling off at the minimum descent altitude (MDA) of 700 feet, Gao continued his shallow left turn, then straightened out onto the downwind leg, paralleling the runway. However, no one commented on the fact that they were much too close to the airport — again, in the absence of a thorough approach briefing, it probably wasn’t on their minds.

Barely a minute after straightening out on the downwind leg, flight 129 passed abeam the north end of runway 18R/36L. At this point, the circling approach procedure called for the base turn to begin after 20 seconds. Captain Wu set a timer for 20 seconds, but in fact, this was too much: they were flying 15 knots faster than the appropriate circling approach speed, and they had a tailwind. Both these factors meant that a 20-second wait after passing abeam the runway end would take them farther out away from the airport than necessary.

The path of flight 129, overlaid with the correct approach pattern and the CVR transcript. Map source: Google

While the timer counted down from 20 seconds, the approach controller called flight 129 and gave the pilots the radio frequency on which to contact the tower controller, who would clear them to land. But the pilots were so preoccupied with the complex approach that they didn’t hear the transmission. Only after calling the plane on the emergency “Guard” frequency were they able to get through, at which point they finally contacted the tower controller. During this same period, First Officer Gao became uncomfortable with the strong winds, turbulence, and sketchy visibility. He willingly gave up command to Captain Wu, who announced, “I have control.” This was in fact a terrible mistake: during a complex maneuver, pilots should not exchange roles because they risk losing track of their expected duties. But Captain Wu was more concerned about his first officer’s ability to handle the deteriorating weather conditions, which for him outweighed his theoretical responsibility to say, “No, you keep flying.”

With the sudden change of command, Captain Wu and First Officer Gao effectively swapped duties, but there was no time to discuss who should do what. The result was that Wu ended up doing the jobs of both pilots. After the end of the 20 second timer, he realized it was time to begin the base turn and announced, “Turning right.” But at that moment, the tower controller issued their clearance to land, and he delayed the turn while listening to the transmission.

The path of flight 129, overlaid with the correct approach pattern and the CVR transcript. Map source: Google

“Turn quickly, not too late,” Gao advised him.

However, they were too close laterally to the runway — they couldn’t actually turn tightly enough to line up with it. Apparently recognizing this, Wu started turning left instead of right in an attempt to swing wide and make the turn easier. By the time he finally turned right to enter the base turn, 15 seconds after the end of the timer, flight 129 was 3.3 kilometers farther from the airport than it should have been.

As flight 129 began its base turn, the tower controller lost sight of the plane behind a cloud. Doubtful that the pilots could still see the runway, he contacted them and asked, “Air China 129, can you landing?”

But Second Officer Hou replied, “Roger, QFE 3000, Air China 129,” a response that was not connected in any way to the question the controller had asked. At that exact same moment, the approach controller also observed that the plane had disappeared into a cloud. He called the tower controller and asked, “Does it seem go around,” inquiring whether flight 129 intended to abandon the approach. But this transmission overlapped with Hou’s reply and the tower controller never heard it.

“Air China 129, say again your intention,” said the controller. But there was no response.

As flight 129 plowed deeper into the cloud, Wu said to Gao, “Help me find the runway.”

But Gao didn’t answer the question, instead commenting on the fact that their altitude had slipped slightly below 700 feet. “Pay attention to the altitude keeping,” he said. “Pay attention to the altitude!” By now it was probably not possible to see the runway through the clouds, but none of the pilots made note of this, despite the fact that the approach procedure called from them to go around if they lost sight of the runway.

At 11:21, twelve seconds after he first queried Gao about the runway, Wu again asked, “[Do you] have the runway in sight?”

“No, I can’t see out,” Gao replied. “Must go around!”

But Captain Wu didn’t react. Believing that there was no great urgency to make a missed approach, he planned to do it only once he had rolled out of the base turn. What he didn’t realize was that they had strayed so far outside the normal approach pattern that flight 129 was on a collision course with nearby Mount Dotdae.

The path of flight 129, overlaid with the correct approach pattern and the CVR transcript. Map source: Google

Within seconds of Gao’s request to go around, a tree-covered ridgeline suddenly appeared through the rain. Gao screamed, “Pull up! Pull up!” and Wu pulled back hard on his control column, but it was too late. As it struggled to climb, the Boeing 767 struck trees just below the top of the ridge. The tail hit the ground first and the fuselage shattered on impact, sending flames tearing through the passenger cabin. Burning wreckage tumbled up and over the top of the ridge, scattering pieces of the plane along a 200-meter-long swathe of flattened forest.

Dramatization and simulation of the crash of Air China flight 129. Video source: Mayday (Cineflix)

The crash instantly killed the majority of the passengers, as well as First Officer Gao and Second Officer Hou. However, some people survived the brutal impact, regaining consciousness amid tangled wreckage and burning jet fuel. Toxic smoke quickly filled what remained of the cabin as badly wounded passengers struggled to escape. Many people became trapped after their seats came loose and jammed their legs under the rows in front, while others quickly undid their seatbelts and fled through breaks in the fuselage. Both of the rear flight attendants survived, and one managed to free a trapped passenger as he shouted for the survivors to run away from the plane. Pillars of fire shot into the sky as they fled for their lives.

In the cockpit, Captain Wu survived the crash, somehow managing to drag himself away from the plane despite suffering serious injuries. Most of the others who survived were seated in the middle section between rows 21 and 33 at the back of the plane, which was most sheltered from the impact forces and post-crash fire.

The runway could be seen clearly from the crash site. Image source: Mayday

Within a minute of the accident, a local resident who heard the crash called emergency services, and a rescue team immediately set out to reach the site. Ten minutes after the crash, while the rescuers were still on their way, two survivors managed to dial the emergency number on their mobile phones and also reported the accident. The tower controller tried to contact the plane ten times over two minutes but received no answer; yet he didn’t seem to consider the possibility that the plane had crashed until more than 20 minutes later, at which point he finally picked up the crash phone and reported the accident — the first attempt to do so through the official reporting channel, which is normally the first source of information about a downed aircraft. By that time, rescue personnel were already on site trying to help the survivors.

Another aerial view of the crash site.

In all, 129 people lost their lives, including two who died in the hospital after the crash, making Air China flight 129 the deadliest air disaster ever on South Korean soil. Only 37 survived, including two flight attendants and Captain Wu Xinlu. Many of the surviving passengers came from a single South Korean tour group, and were saved by a strange twist of fate. Upon arriving at the airport, their tour guide realized he had left his passport and bag at the hotel, and they were forced to go back for them. By the time they arrived at the gate, the good seats had been taken, forcing them to sit in the back of the plane — which just so happened to be the safest place to be during the crash. In interviews, many of the Korean survivors also put forward a complaint: they couldn’t understand the pre-flight safety briefing, which was only in Mandarin and English. Whether this caused any injuries or deaths is difficult to know.

Seating locations of survivors and fatalities. Image source: the KAIB

In investigating the crash, Korea’s Aviation-Accident Investigation Board (KAIB) zeroed in on the actions of the pilots, and to a lesser extent on the actions of the air traffic controllers. Regarding the former, there appeared to be several underlying factors that contributed to the outcome. First, there were questions about the adequacy of the training provided to the pilots by Air China. During training, they were required to fly just one circling approach — which was conducted at Beijing Airport, where there were no terrain obstacles to worry about. Having never performed a circling approach at Gimhae Airport and with little or no practice at other similarly hilly airports, they might not have been conditioned to factor high terrain into their calculations. Furthermore, Korean and Chinese policies differed on a key point: Korean rules included Gimhae as a “special” airport that required additional training before pilots could land there, but Chinese rules gave it no special status, meaning that the crew of flight 129 lacked this extra layer of familiarity with the airport that was afforded to Korean pilots.

The pilots also displayed poor crew resource management (CRM): they failed to adequately delegate duties, communicate information to one another, and maintain a collective picture of what was happening. But Air China pilots supposedly received CRM training — so what went wrong? As it turned out, the CRM training came in the form of lectures on theory and lacked any actual practice scenarios. In all likelihood, the pilots knew the basic principles of CRM, but had no knowledge of how to apply them. Unfortunately, Air China’s training program seemed to have completely missed the point of CRM.

Another aerial view of the crash site. Image source: the KAIB

The cockpit voice recording clearly showed that the pilots flew an unstabilized approach — that is, they were not on the normal landing track. They turned too close to the airport on the downwind leg and made the base turn too late. The prudent thing to do would have been to abandon the approach and try again, but they did not — even after they lost sight of the runway, which is supposed to trigger an immediate go around. Furthermore, Captain Wu was obligated to go around immediately if any crew member told him to — but when First Officer Gao said “Must go around,” he didn’t react until he saw terrain ahead. Had he initiated a missed approach immediately, as called for in the standard operating procedures, they probably would have missed the mountain. Investigators interviewed Captain Wu in his hospital bed to try to understand why he didn’t go around earlier, but he claimed he didn’t remember anything unusual about the approach until they lost sight of the runway. This conflicted with the flight data showing he deviated left before starting the base turn, which suggested he was aware they were too close laterally to the runway. Unfortunately, the KAIB was unable to get much useful information out of the devastated captain, whose memory of the incident had suffered as a result of his injuries.

A photo taken shortly after the crash captured the fuselage in flames. Image source: the KAIB

In all likelihood, the pilots succumbed to tunnel vision, where they became so focused on completing the task of landing that they were unable to step back, see the big picture, and realize it would be safer to abandon the approach and start over. But one last line of defense that could have saved them was conspicuously absent: the Ground Proximity Warning System, or GPWS, never activated before the impact with terrain. Investigators found that the GPWS installed on the 17-year-old Boeing 767 was a primitive model dating back to the early 1980s that was incapable of detecting the type of terrain collision that occurred on flight 129. This outdated system would only go off if the plane exceeded a particular closure rate with the ground below; in this case, 2,253 feet per minute. However, at no point during the flight up until the moment of impact did their closure rate exceed 1,800 feet per minute. The GPWS didn’t fail; rather, the criteria to set it off were not met. This wouldn’t have happened with a modern Enhanced Ground Proximity Warning System (EGPWS), which could also detect high terrain ahead of the aircraft and would sound the alarm at least 30 seconds in advance.

Crews remove burned wreckage at the crash site. Image source: the Bureau of Aircraft Accidents Archives

Investigators also had to ask why the air traffic controllers didn’t notice that flight 129 was off course. Gimhae Airport was equipped with a Minimum Safe Altitude Warning (MSAW), a system that detects when a plane near the airport is too close to terrain and sends an alert to air traffic controllers. When flight 129 strayed beyond the approach pattern into an area where the minimum safe altitude was greater than 700 feet, it should have triggered a warning. But investigators found that the MSAW system only produced a visual warning on the tower controller’s radar screen, not an audible one, and the tower controller wasn’t looking at his radar. The job of the tower controller is to handle planes in very close proximity to the airport during takeoff and landing, allowing him to track planes visually through the windows. Radar was a supplement that tower controllers usually only used to make an initial determination of the plane’s location before identifying it visually. Therefore, as soon as the tower controller spotted flight 129, he stopped looking at the radar. But when the flight disappeared into a cloud, he continued trying to make visual contact with the plane, even though it would have been more prudent to switch to tracking it on radar. Had he done so, he might have seen the MSAW alert and ordered the plane to go around. The approach controller realized that with the plane hidden behind a cloud, its approach shouldn’t continue, but his call to the tower controller was canceled out by a transmission from flight 129 — an unfortunate coincidence that might have prevented the tower controller from realizing the urgency of the situation.

How MSAW works, in simple terms. Image source: Aviation Impact Reform

After reviewing all the evidence, Korean and Chinese investigators disagreed about how to apportion responsibility for the accident. While acknowledging that air traffic controllers could have been more proactive in preventing the crash, the KAIB placed most of the blame on the pilots and their training, which led to a breakdown in communication and the continuation of an unstable approach. But the Chinese CAAC felt that the KAIB had missed some important points about the controllers. First, there was some confusion about flight 129’s “approach category” — that is, the set of weather and altitude minima that apply to a plane based on its size and speed. Normally, a Boeing 767–200 falls under approach category C, which has a minimum descent altitude (MDA) at Gimhae of 700 feet. But when the pilots flew at speeds exceeding 140 knots, this bumped them into approach category D, which had an MDA of 1,100 feet. Chinese investigators felt that the Gimhae controllers didn’t understand how the approach category system worked, and that if they had, they might have used a higher MDA that would have kept flight 129 clear of the mountain. Second, some of the approach controller’s transmissions were difficult to understand, which caused gaps in communication and increased the workload in the cockpit at critical moments, including during the period just before the start of the base turn. Third, the approach controller is thought to have been tracking flight 129 on radar and therefore must have seen the MSAW alerts, but didn’t treat them with the appropriate urgency. And finally, a hangar obstructed the view to the north from the airport’s weather observation station, limiting the weather observer’s ability to detect the low clouds hanging over the runway 18R circling approach area. But while these are all valid points, none of them would have mattered if the pilots had followed proper procedures, and the KAIB felt that elevating them to the level of “probable cause” alongside the flight crew’s actions was inappropriate.

Part of the plane’s tail lies amid broken trees after the crash. Image source unclear

In its final report, the KAIB issued a long list of safety recommendations to help ensure that a similar accident won’t happen again. These included better circling approach and CRM training at Air China, as well as better standardization of procedures and materials used by the airline, which had come under criticism by the CAAC in 2001 for lacking documentation and operating on an almost informal, ad-hoc basis. Other recommendations aimed at Air China and the CAAC included that they provide approach charts for every member of the flight crew; that they install EGPWS on their aircraft; and that safety announcements on flights to Korea be conducted in Korean as well as English and Chinese.

To Korean authorities, the KAIB recommended that circling approach patterns be displayed on controllers’ radar screens to make it easier to spot an aircraft flying off course; that Gimhae Airport install lights on obstructions near the circling approach path; that Gimhae Airport conduct drills to prepare its employees for the possibility of an accident outside the airport boundary; and that air carriers submit a plan to assist victims of an accident, among other points. Further recommendations to various parties included that an ILS approach to runway 18R be developed to reduce the need for circling approaches, and that the weather observation site be moved to a place with an unobstructed view. These changes have made it safer both to fly to Busan and to fly on Air China, and flight 129 remains the airline’s only fatal accident.

Branches caught inside the bogie show that the plane’s landing gear was extended at the moment of impact. Image source: Mayday

The crash of Air China flight 129 is valuable as a teachable moment. For much of aviation history, “controlled flight into terrain,” or CFIT, accidents have been the leading cause of airline passenger fatalities. Virtually all of these accidents involve pilot errors, and often the same relatively small set of mistakes. One of the most common is the failure to conduct a proper approach briefing, especially after encountering a last minute runway change, as happened on flight 129. It is important that pilots be mentally prepared for every step of the approach before actually conducting it. Failing to brief the approach can allow the airplane to get ahead of its pilots — a dangerous situation under any circumstances, as several other accidents can also attest. In 1996, Vnukovo Airlines flight 2801 crashed in Svalbard killing all 141 people on board during a complex approach for which the pilots skipped the approach briefing. In 1997, 229 people were killed when Korean Air flight 801 crashed on approach to Guam — once again, the crew had skipped critical parts of the approach briefing. In 1995, 159 people died when American Airlines flight 965 flew off course and crashed on approach to Cali, Colombia, while trying to handle a sudden runway change; the CVR revealed no evidence of an approach briefing. The lesson from these accidents is clear: never neglect the approach briefing.

Excerpts from other aircraft accident reports highlight the tragic fates of other flight crews who didn’t conduct approach briefings.

Today, CFIT accidents, like all types of crashes, are on the decline. Nevertheless, they continue to happen, with another major CFIT accident occurring every 1–3 years. In its report on the crash of Air China flight 129, the KAIB cited a 1996 report on CFIT accidents which found that one of the most effective ways to prevent such crashes is for pilots to learn about them. The study found that pilots who had reviewed the causes and contributing factors of previous pilot error accidents were far less likely to repeat those mistakes.

Pilots are human, and they will always make errors. In the wrong place at the wrong time, those errors can lead to tragedy, as they did on flight 129. The ultimate folly would be to believe that we are better than Captain Wu Xinlu and First Officer Gao Lijie, because ignorance of one’s own limitations is a recipe for disaster. If there’s anything in which Wu may take solace as he struggles to move on from the crash for which he was blamed, it’s that others can study flight 129 and come away with important lessons that might save lives in the future.

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Analyzer of plane crashes and author of upcoming book (soon™). Contact me via @Admiral_Cloudberg on Reddit or by email at kylanddempsey@gmail.com.

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