Safety on a Budget: The crash of Sriwijaya Air flight 182

An official inspects pieces of Sriwijaya Air flight 182 lined up on the dock in Jakarta. (Reuters)

On the 9th of January 2021, an aging Boeing 737 flying for an Indonesian budget airline disappeared from radar minutes after takeoff from Jakarta. Flight tracking data revealed that the seemingly normal flight had come to a shockingly sudden end, turning over and plunging straight into the sea from 10,000 feet in less than 30 seconds. By the time rescuers arrived at the scene in the waters near the Thousand Islands, the only signs of the plane were bits of pulverized debris floating on the surface of the Java Sea — none of the 62 people on board had survived.

After a painstaking search for the black boxes, a deep dive into the plane’s avionics, and a frustratingly speculative analysis of some of the pilots’ more baffling actions, Indonesian investigators released their final report in November 2022, at last revealing to the world how Sriwijaya Air flight 182 ended in disaster. The story is not one which should inspire confidence in the state of Indonesia’s aviation industry, already considered one of the most dangerous in the world. It is a story of a convergence of failures at every level, from the airline to the pilots to the plane itself, which never should have been allowed to happen in 2021, delivering a grim indictment of Indonesia’s ability to enforce the lessons of countless previous accidents.

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A 2009 timetable for Sriwijaya Air seems to have been an exercise in jamming as many different fonts onto one poster as possible. (Airline Timetable Images)

In 2003, at the dawn of Indonesia’s aviation boom, a group of businesspeople acquired an aged Boeing 737–200 and vowed to start a low cost airline. They christened their company Sriwijaya Air, a name which broadcast its founders’ grandiose ambitions, invoking the medieval Srivijaya kingdom which once ruled much of what is now Indonesia and Malaysia. Like the kingdom, the airline started out small, using its single 737 to ferry passengers back and forth between Jakarta and Pangkal Pinang, hometown of cofounders Chandra and Hendry Lie. In the mid-2000s, it was almost impossible to lose money operating an airline in Indonesia, so Sriwijaya Air quickly began to grow, driving a competing ferry service out of business within months as it expanded its fleet and its schedule. In fact, it grew so rapidly that by 2011, eight years after its founding, it was the third largest airline in Indonesia, and was giving flag carrier Garuda a run for its money. All this was achieved on the back of ticket prices that often ran well below 20 USD.

Behind the scenes, however, not all was well. Sriwijaya Air’s finances were said to be opaque, in large part because the company was still wholly owned by its founders and repeatedly rebuffed rumors of a pending IPO. By 2017, the airline was actually losing money on a massive scale, a fact which only became apparent in November 2018, when Garuda announced a wholesale takeover of Sriwijaya Air’s finances and operations. This was more of a rescue than an acquisition — the plan seemed to be to reform the company until it could be made profitable, then let it go. But Sriwijaya Air was not an easy subject for reform, as its managers seem to have agreed to the deal only reluctantly, and it was unclear who was going to pay a $175 million debt which the airline had racked up in unpaid fees to state-owned airports, oil companies, and Garuda itself.

PK-CLC, the airplane involved in the accident, seen here in 2019. (Leony Eka Prakasa)

The partnership between Garuda and Sriwijaya Air was unstable from the start, and by September 2019, it appeared to be on the verge of collapse. On September 25th, Sriwijaya Air threatened to pull out of the deal after firing several Garuda directors who it claimed had been appointed without prior approval. Garuda responded in kind, removing its logos from Sriwijaya Air planes, while Sriwijaya Air’s Singapore-based maintenance contractor terminated its service because of unpaid debts. The two sides briefly managed to reconcile, but the deal fell apart again in November 2019, this time for good. The details are murky, but it has been claimed that Sriwijaya Air had defaulted on its debt and concealed this from Garuda. Reports at the time indicate that the airline was forced to ground more than half its fleet because it was unable to service the aircraft, and passengers experienced repeated disruptions as a large percentage of Sriwijaya Air’s scheduled flights failed to materialize without explanation.

Sriwijaya Air in fact came out of the Garuda partnership as a shell of its former self, lacking senior management, maintenance contractors, qualified engineers, maintenance facilities, a maintenance manual, spare parts, ground handling and catering contractors, and more, on top of insufficient revenue and large outstanding debts. An internal risk analysis concluded that all these issues needed to be rectified before the airline could operate a single flight safely. The company appears to have scrambled to fill these gaps with remarkable speed, however, as it does not seem that its services were ever completely suspended. Indonesia’s Directorate General of Civil Aviation, or DGCA, announced emergency inspections of the airline following its divorce from Garuda, but it is unclear what they found, as no public report has emerged.

In any case, as 2019 rolled over into 2020, Sriwijaya Air was probably in poor condition, both financially and operationally. And then out of the blue came the Covid-19 pandemic, causing airline travel to plummet worldwide. Considering this confluence of events, it’s remarkable that Sriwijaya Air even survived to see the year 2021.

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The six crewmembers of flight 182. Although the photographs are not labeled, Captain Afwan and First Officer Mamahit appear to be the first and second from the left, respectively. (Aviation Voice)

By December 2020, air travel was beginning to pick up again, and Sriwijaya Air, like airlines around the world, was calling back up the aircraft which had been grounded during the pandemic. One of these planes was PK-CLC, a 26-year-old Boeing 737–500 built in 1994 and transferred to Sriwijaya Air in 2012. PK-CLC had been grounded from March 23rd until December 20th, 2020, presumably due to the coronavirus — the official report says it was down for maintenance, but the length and timing of the grounding suggest otherwise.

PK-CLC had only been back in service for three weeks when it pushed back from the gate in Jakarta on the afternoon of January 9th, 2021. The 737, which was bound for the city of Pontianak, was less than half full, with only 56 passengers on board, including six deadheading Sriwijaya employees. There would have been 57, but one passenger was said to have been turned away because he tested positive for Covid-19.

In addition to the 56 passengers, the flight also featured a crew of six, including four flight attendants and two pilots. In command were 54-year-old Captain Afwan (who like many Indonesians uses only one name) and 34-year-old First Officer Diego Mamahit. Both were highly experienced on the Boeing 737, with nearly 14,000 combined hours on the type, out of 22,000 hours total.

The route of Sriwijaya Air flight 182. (Google, annotations mine)

At 14:36 local time flight 182 took off from Jakarta and began climbing toward 29,000 feet, as cleared by Air Traffic Control. The weather was overcast with some scattered thunderstorms, but otherwise normal. So were the events on board the plane, as the pilots carried out routine checklists and monitored the autoflight systems.

In accordance with standard procedures, the pilots flew the plane with the autopilot and autothrottle engaged beginning shortly after takeoff. Rather than directly manipulating the controls, they sent commands to the autopilot (which in turn communicated with the autothrottle) using the Mode Control Panel, or MCP. Using the MCP, they could enter target headings, altitudes, speeds, and rates of climb, and the autopilot and autothrottle automatically worked together to achieve and then hold these target values.

Two minutes after takeoff, as flight 182 was climbing through 5,400 feet, the pilots used the Mode Control Panel to change the autopilot’s vertical mode to “vertical speed” in order to reduce their rate of ascent for the transition between the initial and intermediate climb phases. Using the vertical speed knob on the MCP, they set a target climb rate of approximately 2,000 feet per minute.

Moments later, the pilots spotted a thunderstorm in the distance, and First Officer Mamahit asked Captain Afwan if they should turn right onto a northeasterly heading of 070 degrees to go around it. The cockpit voice recorder did not capture most of Captain Afwan’s statements, but he must have suggested a slight modification of the plan, since Mamahit ultimately asked air traffic control for a diversion to 075 degrees. The request was granted immediately. With the autopilot’s lateral mode set to “heading select,” Captain Afwan used the heading knob to enter a target value of 075˚, and the autopilot began to turn the plane to the right.

An example of what the thrust levers on a Boeing 737–500 would look like during an asymmetric thrust condition. Note that in the photo, the left engine is at high power, not the right one. (MAK)

Meanwhile, the reduction in the commanded rate of ascent meant that less engine power was needed to maintain the same airspeed. As a result, the autothrottle began to reduce engine power to prevent the speed of the plane from increasing.

The Boeing 737’s autothrottle automatically controls engine thrust by physically driving the thrust levers in the cockpit. There is no separate engine control system — the automatic system moves the levers like a pilot would, and the thrust output is determined by the position of the thrust levers, exactly like in manual flight.

When the autothrottle commanded a decrease in engine power, a motor engaged to drive the thrust levers back from the max climb position. Normally the levers are supposed to move together, but this time, something unexpected happened: the left thrust lever started rolling back, but the right thrust lever didn’t move. As a result, the right engine power setting, measured in terms of its fan rotation speed, or N1, remained at 91.8%, while N1 on the left engine began continuously decreasing.

At first, nobody noticed. As this was occurring, the controller contacted the flight and instructed the pilots to level off at 11,000 feet to make room for crossing traffic. In response, Captain Afwan reset the target altitude in the MCP to 11,000 feet. Thirty seconds later, a chime sounded to inform the crew that they were 1,000 feet from their target altitude, and First Officer Mamahit announced that they were approaching 11,000.

All the while, the plane remained in a sweeping right turn, passing through due north on its way to a heading of 075. But with the right engine still at max climb and the left engine still rolling back, the thrust asymmetry increasingly tried to push the plane the other way, to the left. To counteract this tendency, the autopilot had to turn the pilots’ control wheels farther and farther to the right.

The flight path of flight 182, with its major changes in direction highlighted. (BBC and Flightradar24, some annotations mine)

Approximately 40 seconds after the thrust lever positions first began to diverge, the left engine N1 speed was 62.7% and decreasing, while the right engine N1 speed was still 91.8%. At this point the asymmetry became so large that the autopilot had to use its full roll authority to keep the plane turning right. The pilots’ control columns reached 19 degrees of rightward deflection, and then stopped — although the pilots themselves could have turned much farther, 19 degrees of control wheel deflection was as much as the autopilot could command. Still, the size of the thrust asymmetry kept increasing, until it overpowered the autopilot. The plane reached a heading of 046 degrees, leveled off, and then began to turn back to the left, even as the autopilot continued its futile efforts to turn to the right.

Still seemingly oblivious to the problem, First Officer Mamahit called out “set standard,” switching the barometric pressure setting from the local reading to the standard value. The plane was rolling left at a rate of about one degree per second and increasing, while the left thrust lever was still rolling back toward idle, but no one noticed.

At that moment, ATC instructed flight 182 to climb to 13,000 feet, and Mamahit read back the instruction. This would be the last communication from the flight — in fact, disaster was already just seconds away.

Captured amid the background noise on the First Officer’s mic, Captain Afwan could be heard saying, “One three zero.”

“One three zero,” Mamahit repeated. The bank angle was still increasing, passing 30 degrees to the left. The plane’s heading passed back through due north and began to track in a northwesterly direction.

Suddenly, at 14:40 and three seconds, an automated voiced began to call out, “BANK ANGLE! BANK ANGLE!”

“Eh!?” Captain Afwan exclaimed.

“Eh, sorry!” said First Officer Mamahit.

“BANK ANGLE!” the alert blared again.

“Bank angle!” Mamahit shouted.

The plane was already banked 37 degrees to the left, beyond the maximum roll angle normally used in flight, when the bank angle warning sounded. The alert immediately captured the pilots’ attention, and Captain Afwan reached for his control column, disconnecting the autopilot with a loud cavalry charge alarm. And then, seemingly without thinking, he attempted to recover — by turning even farther to the left!

This diagram produced based on ADS-B data broadcast from the flight shows just how quickly it plunged into the sea. (AFP and Flightradar24)

Afwan only held the wheel to the left for four seconds, but by the time he realized his mistake and wrenched it back the other way, the damage had been done. Banking through ninety degrees to the left, the wings lost lift and the plane began to descend. As they turned over into an inverted dive, First Officer Mamahit frantically shouted, “Captain, captain! Upset, upset!”

For a moment, 62 lives hung in the balance — and then Captain Afwan sealed their fate. Desperate to stop the plane from diving, he pulled the nose up sharply, only to discover that pulling up while inverted sends the plane straight toward the ground instead. In the blink of an eye, the 737 plunged into an inverted spiral dive, plummeting toward the ocean just a few thousand feet below. The rapid, chilling clackclackclack of the overspeed warning burst suddenly into life as they exceeded the 737’s maximum speed. “Captain! Captain!” First Officer Mamahit screamed, as the plane spun a full 360 degrees, through upside-down and back to right-side-up. Seconds later, Captain Afwan managed to level the wings and pulled the nose almost level, but by then it was already too late. With a mighty roar, Sriwijaya Air flight 182 plowed belly-first into the shallow waters of the Java Sea at immense speed, instantly destroying the airplane and killing all 62 passengers and crew. Only 25 seconds had passed since the first bank angle warning.

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Recovery crews pull pieces of the 737 from the Java Sea. (New York Times)

On the nearby island of Lancang, the massive impact rattled windows with a sound like thunder. Out on the water, fishermen ducked for cover as the crash sent mangled shards of metal and composites flying over their heads, leaving the bright blue sea strewn with the twisted remains of the 737. Some were so close that they caught sight of red-and-yellow debris hurtling through the water directly beneath them. These and other witnesses hurried to the scene in their boats, hoping against hope for survivors, but they could barely find anything bigger than a meter square. It was obvious that nobody had survived.

By the time rescue services reached the scene, the rescue was already a recovery. Few, if any bodies were found intact. So extensive was the destruction that some victims were never identified, and toxicological testing of the pilots’ tissues proved impossible.

KNKT investigators examine an unidentified piece of wreckage. (Reuters)

Investigating the cause of the crash fell to the National Transportation Safety Committee, known by its Indonesian acronym KNKT. Unfortunately, the scenario was all too familiar: this was the third time in just over six years that they had been dispatched to investigate the crash of an airliner in the Java Sea.

The first priority in any investigation is to find the black boxes, and this case was no different. The flight data recorder was found within days, but when divers reached the locator beacon for the cockpit voice recorder, they found that the recorder had disintegrated, and the memory card was nowhere to be seen. The only solution was to methodically scour the sea floor in the vicinity of the crash site until the memory card was found, no matter how long it took — and until then, investigators would have to learn what they could from the FDR.

The data revealed that the first three minutes of the flight were normal, until the autothrottle attempted to reduce thrust to achieve the lower rate of climb selected by the crew. When it did so, something went wrong: the right thrust lever didn’t move, while the left thrust lever kept going all the way until it reached the flight idle position. The autothrottle appeared to have decreased thrust on the left engine to a level well below the normal value for that phase of flight in order to compensate for the fact that the right engine was still at max climb power. But that shouldn’t have happened — the autothrottle should have disconnected automatically well before then, as soon as a major difference between the thrust lever positions was detected. That left the KNKT with two mechanical questions: why didn’t the right thrust lever move when it was commanded to do so, and why didn’t the autothrottle immediately disconnect?

Among the debris laid out on the dock, you can see a piece bearing part of the plane’s registration number, PK-CLC. (ABC News)

Answering the second question required investigators to dive into the history and design of an obscure safety system called the Cruise Thrust Split Monitor, or CTSM. The Boeing 737–500 did not come from the factory with CTSM installed, but Boeing introduced the system following a series of incidents involving asymmetric thrust with the autothrottle engaged, and its installation was made mandatory by an FAA airworthiness directive in 2000. The accident airplane was among those fitted with the system.

The CTSM was designed to disconnect the autothrottle if the autothrottle could not correct a thrust asymmetry. It would activate only when three criteria were satisfied. First, the thrust lever position sensors had to detect a significant difference between the positions of the two thrust levers, with the exact size of the required difference depending on several factors, including flap setting and airspeed. Second, the autothrottle could not be in go-around mode. And third, as a form of redundancy, the flight spoilers — which activate to assist the ailerons when the pilot banks the airplane — needed to be deflected by more than 2.5 degrees. The motion of the flight spoilers would indicate that either the pilot or the autopilot was trying to compensate for the thrust asymmetry by rolling against it, thus confirming that the asymmetry was, first of all, real; and second, undesired.

The average size of the wreckage pieces provides some indication as the the force of the impact. (Reuters)

If the system had operated in accordance with its design specifications, it should have caused the autothrottle to disconnect within a few seconds after the difference in thrust lever positions began to develop at about 14:39:00. Instead, the autothrottle remained engaged, continuing to roll back the left thrust lever, making the asymmetry progressively worse, until it finally clicked off at 14:40:10. The fact that it did eventually disengage suggested that the system was working, albeit with a delay, and the precise timing provided a clue as to why. In fact, the autothrottle disengaged as soon as Captain Afwan turned the control wheel beyond the 19 degrees commanded by the autopilot. This suggested that the problem was that the spoiler position sensor was providing the CTSM with a value that was too low. Although the spoilers deflected more than 2.5 degrees when the autopilot turned the control wheel 19 degrees to the right, the value sent to the CTSM was less than 2.5 degrees, so the system did not activate. When Captain Afwan moved the control wheel even farther, the spoiler deflection increased, the transmitted value surpassed 2.5 degrees, and the autothrottle disconnected. But by that point the left engine was already at idle power and the plane was already out of control.

In the end, the relevant aircraft components were never found, so the KNKT could not determine why the spoiler deflection values transmitted to the CTSM were too low. The most likely explanation, however, was that the sensor had been rigged improperly last time it was serviced. Sriwijaya Air said it had never touched the spoiler position sensor, so if this was the case, the problem had likely been introduced prior to 2012, when the plane was still in service in the United States. The lack of any requirement to inspect the sensor would have prevented the discovery of the problem until it made itself apparent during the accident flight.

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Some choice pieces were presented to journalists at a news conference. (Basarnas)

The second mechanical question facing investigators was why the right thrust lever didn’t move from the max climb position.

As it turned out, the KNKT investigators were not the first to ask. PK-CLC’s maintenance history in fact showed that since the first such report in November 2013, pilots had recorded 65 autothrottle malfunctions in the plane’s technical log, and there had been 61 reports of asymmetric thrust in flight, beginning at around the same time. These reports continued periodically for the next seven years, right up until the crash in 2021, even though engineers carried out corrective actions every single time.

Since the components of the autothrottle system were shattered into countless pieces on the bottom of the sea, the best way for KNKT investigators to narrow down the cause of the recurrent autothrottle difficulties was by examining what could not be the cause, based on the actions taken by engineers. Investigators noted that the majority of the “corrective actions” taken in response to the autothrottle problems consisted of cleaning the connectors on the autothrottle computer, re-racking the computer, and testing the integrity of the computer’s software and hardware using its built-in test equipment (BITE). In each case, the BITE tests passed, and the system was returned to service. Of course, the fact that malfunctions continued to occur strongly suggested that dirty connectors were not the issue. And yet engineers continued to perform these very basic quick-fixes over and over again, apparently unaware that this was a chronic issue, and that everything they were doing had already been tried. In their report, the KNKT openly speculated that engineers defaulted to cleaning the connectors and running the BITE tests because it was easy, not because they thought it was likely to solve the problem.

A badly damaged engine core was among the largest pieces recovered. (Tempo.co)

According to the log books, these problems resurfaced almost immediately after the plane was taken out of pandemic storage in December 2020. In response, the autothrottle computer was replaced on December 30th. Therefore, the fact that the problem happened again on the accident flight proved that the repeated malfunctions were not the result of a computer problem. The autothrottle servo — the motor which moves the thrust levers — was also ruled out, since it was recovered after the accident, and no defects were found. Nor could the problem have been with the right engine itself, since it was replaced multiple times between 2013 and 2021.

There was, however, one more major suspect: the linkages between the servo motor and the thrust levers themselves. Although these linkages were not recovered, excessive friction in the right thrust lever linkage would explain the recurring thrust asymmetry.

The reason lay in a device called the autothrottle torque switch. The purpose of the torque switch is to allow the pilot to override the autothrottle by applying force to the thrust lever. If the autothrottle encounters more than 2 pounds of resistance while attempting to move the thrust lever, the torque switch will trip, disconnecting the servo motor from the affected thrust lever so that the pilot can move the lever without fighting the motor. However, if there is excessive friction in the linkage, the torque switch could be tripped even when the pilot is not overriding the autothrottle, causing the affected thrust lever to unexpectedly stop moving during normal autothrottle operation. If only the right thrust lever linkage was affected, then the left thrust lever would have continued to move, creating the thrust asymmetry.

Underwater images show airplane debris mixed in with personal effects, such as a child’s Marvel backpack.

As it turned out, there was a troubleshooting procedure in the manual which would have eventually led maintenance engineers to the source of the issue, but during the entire seven-year period since the malfunctions began, no one ever referred to it. This type of failure was not unexpected; it had in fact been anticipated and accounted for in the troubleshooting tree produced by the manufacturer. But instead of sitting down and taking a day to go through all the steps, engineers just kept cleaning the connectors, running the BITE tests, and calling the problem fixed. Records indicated that fewer than 50% of the engineers even looked at the maintenance manual while troubleshooting the autothrottle, and when they did, they only referred to the sections related to the BITE tests. Of course, the BITE tests on the computer always passed, because the computer wasn’t the problem.

The failure to conduct more intensive troubleshooting came about because Sriwijaya Air’s maintenance personnel didn’t know they were dealing with a chronic, recurring failure. If they had, then it would have been obvious that their actions were inadequate. This might have come about due to the poor state of Sriwijaya Air’s maintenance services following its bloody divorce from Garuda, but even if everything had been done by the book, the airline’s definition of a “recurrent defect” might have obscured the problem. According to company policy, a recurrent defect subject to enhanced troubleshooting measures was one which recurred at least three times during a period of 15 flights or less. Because Sriwijaya Air’s planes were operating frequent short-haul flights, this limit was excessively restrictive, since 15 flights did not add up to enough flight hours for most defects to actually recur three times. The autothrottle problem, which was only reported once every few weeks, certainly failed to qualify.

On the surface of this battered piece of fuselage skin, every gouge tells a story. (Reuters)

That having been said, it turned out that thrust asymmetry incidents on PK-CLC were much more common than investigators initially were led to believe.

Sriwijaya Air had in place a flight data monitoring program which searched for exceedances in the data downloaded from each plane’s Quick Access Recorder, an alternate flight data recorder which is not crash-protected and is intended for monitoring and diagnostic purposes. The airline had been regularly downloading PK-CLC’s QAR data, but they were unable to actually analyze it because they did not possess the data frames that were required to convert it into a readable format. The KNKT did, however, and when they read out the data, they were surprised to discover that thrust asymmetry events had occurred numerous times in March 2020, December 2020, and January 2021, all without being reported.

The general pattern of most of these incidents was the same: due to a change in flight phase, the autothrottle would attempt to reduce thrust, but the right thrust lever would jam while the left thrust lever kept moving. In some of these incidents, the autothrottle would disconnect, but most of the time it did not, presumably due to the faulty spoiler position sensor. The resulting periods of thrust asymmetry lasted anywhere from 30 seconds to seven minutes before the thrust levers finally got back in sync. The KNKT interviewed the crews who were flying PK-CLC during seven of these incidents, and discovered that five of the seven crews did not recall noticing the thrust asymmetry, nor did any of the crews record the event in the plane’s technical log or report it to the airline.

KNKT investigators examine pieces of an engine. (New York Times)

One of these cases in particular is worth exploring in greater detail. The incident occurred on March 15th, 2020, eight days before PK-CLC was grounded due to the Covid-19 pandemic. During the initial climb, the autothrottle attempted to reduce thrust, but the right thrust lever jammed while the left thrust lever kept moving. The asymmetry grew until the autopilot reached its authority limit, deflecting the control wheel 19 degrees to the right; however, this was insufficient, and the plane began to bank to the left. The captain ordered the first officer to turn to the right, but when he entered the new heading into the MCP, the plane didn’t turn. Moments later, the bank angle reached 41 degrees to the left, well outside the normal operating envelope, triggering automated “BANK ANGLE” warnings. The captain then took manual control of the plane, disengaging the autopilot and autothrottle, but he overcorrected, banking 28 degrees to the right before returning to wings level. Only now did the captain notice the asymmetric thrust and adjust the thrust levers. Incredibly, neither pilot reported the serious incident to the airline or recorded it in the technical log.

The above story was related to the KNKT through the QAR data and during an interview with the first officer. The captain of that flight, however, could not be interviewed — because he was the same Captain Afwan who died in the crash of flight 182.

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Police carry a piece of wreckage onto the pier in Jakarta. (ABC News)

Needless to say, this incident and all the others raised serious questions about the airmanship skills of Sriwijaya Air pilots. Multiple crews had failed to notice asymmetric engine thrust that persisted for several minutes, and some even allowed it to escalate to the point that the autopilot was unable to control the airplane. And in an indictment of the company’s safety culture, most of these pilots didn’t report the events even if they did notice, contributing to the airline’s failure to identify the trend. Although crews did report thrust asymmetry problems 61 times between 2013 and 2021, the real number of incidents must have been an order of magnitude higher.

Of course, a thrust asymmetry is not an emergency. The solution is to simply disconnect the autothrottle, equalize the thrust levers, and continue the flight. The fact that an asymmetry exists should become apparent to the non-flying pilot during their normal instrument scan, either by noticing the position of the levers themselves, by spotting a difference in engine parameters, or by catching the autopilot moving the control wheel to compensate. The fact that many pilots never noticed or noticed only when bank angle warnings sounded was an enormous red flag suggesting that Sriwijaya Air pilots were not performing their normal instrument scans to anywhere near the degree that would be expected.

A piece of wreckage is hauled aboard a recovery vessel. (AFP)

To learn more about what exactly the pilots of flight 182 were doing during the 63 seconds between the emergence of the asymmetry and the first bank angle warning, the KNKT needed to find the missing cockpit voice recorder memory card. For some time after the accident, there were doubts that it would ever be found — but in the end, their efforts paid off. On March 30th, 2021, nearly three months after the crash, divers located the memory card near the edge of the debris field, and it was rushed to a KNKT facility for analysis.

Unfortunately, if investigators were expecting a breakthrough from the CVR recording, they didn’t get one. Captain Afwan’s microphone had suffered an unidentified malfunction which left his channel on the CVR blank. Afwan’s voice could only be heard when he made radio calls, or when he spoke loudly enough to be picked up by the First Officer’s microphone. For the most part, the CVR transcript consisted of disconnected statements by First Officer Mamahit, with Captain Afwan’s presumed replies conspicuously missing.

What the recording did make clear, however, was that neither pilot was occupied with any obvious duties during the period where the plane rolled through wings level and began to turn to the left. When First Officer Mamahit called out “approaching 11,000,” the plane was still banked to the right, and by the time he called out “set standard” 17 seconds later, it was banking to the left. During those 17 seconds, he should have had plenty of time to glance at his primary flight display and observe that the plane was turning the wrong way. For whatever reason, however, he did not — and we will probably never know exactly why.

Recovery crews haul aboard what appears to be part of a landing gear wheel. (Bloomberg)

In any case, the first time either pilot noticed something was wrong came when the left bank exceeded 35 degrees, triggering the automated “BANK ANGLE” warnings. No competent crew should have allowed the plane to drift so far from its intended path, but the KNKT nevertheless identified several factors which could have contributed to their failure to notice the issue earlier. First of all, the plane was flying in clouds — there would not have been a visible horizon, whose movement in their peripheral vision could otherwise have alerted them to the fact that the plane was turning. The fact that the plane was banking left would have to have been discerned by looking at their attitude indicators. However, there were some conflicting cues, namely that their control wheels would have been deflected to the right as the autopilot tried to stop the left turn. Because they expected the plane to be turning right, the control wheels seemed to be right where they should be, and confirmation bias could have led the pilots to subconsciously weight this indication over other indications that they were actually turning left.

KNKT investigators examine an engine fan stage. (Bloomberg)

Even when the bank angle alarm sounded, they were not yet in an emergency situation. The problem could have been easily corrected by rolling back to the right, disconnecting the autothrottle, and restoring the thrust levers to their proper positions. This is what Captain Afwan had done in the March 15th incident. But this time, something caught him off guard, and he immediately reacted by turning the wrong way for four seconds, causing the plane to roll inverted. Now they really were in an emergency.

The same confirmation bias which caused the pilots not to notice their increasing left bank probably contributed to this critical error. If he believed that they were banking to the right as he had instructed the aircraft to do, then when the bank angle warnings sounded, Captain Afwan’s instinct would have told him that the plane was probably banking too far to the right, not too far to the left. Startled by the warnings, his fight-or-flight response engaged, and he reacted to the perceived danger without stopping to assess whether his inputs were reasonable. By the time he realized his mistake and stopped turning left, the plane was already upside down.

At that point, the FDR data showed that Afwan began turning back to the right. If that was all he had done, control probably would have been regained, and this article would have been written on some other accident. But instead, Afwan made one of the most common — and deadliest — errors in recovering from unusual attitudes: he tried to pull the nose up while the plane was still upside down.

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A slide from a promotional presentation about UPRT in the late 90s or early 2000s.

The situation in which Captain Afwan found himself was a textbook scenario from the field of Upset Prevention and Recovery Training, or UPRT. Pioneered in the 1990s and now mandatory in much of the world, including Indonesia, UPRT is designed to present pilots with dangerous aircraft attitudes, such as combinations of high or low pitch, high bank angles, and low or high airspeed, and provides strategies to help them fly their way out.

One of the lessons a pilot ought to learn on day one of upset recovery training is that when the bank angle is greater than 60 degrees, leveling the wings must come first, no matter what else the plane is doing. Even if the plane is rapidly losing altitude, a pilot cannot pull the nose up until the wings are level. If an attempt is made to pull up when the plane is banked between 60 and 90 degrees, the plane will experience an accelerated stall, a terrifying event which need not be described here in detail, but you can use your imagination. And if the bank angle is greater than 90 degrees — that is, if the plane is inverted — pulling up will, quite logically, send the plane diving straight toward the ground.

Instead of heeding this advice, however, Captain Afwan pulled the nose sharply up while inverted, causing the plane to enter a spiral dive. The plane made one full revolution, its bank angle passing through 180 degrees and out the other side, before rolling out with its nose pointed more or less straight down, diving like a lawn dart toward the sea with a peak descent rate of -45,000 feet per minute. At that point, the flight was doomed; although Captain Afwan attempted to recover, there just wasn’t enough room.

Another view of pieces of wreckage arranged on the dock. (New York Times)

The KNKT found it troubling that Afwan would make such a basic mistake even though his records indicated that he had undergone upset recovery training, which had been mandatory in Indonesia since 2018. Although comments on his training record suggested that Afwan was a below average pilot — he had just barely scraped through several examinations with the lowest possible passing grade — there was still probably more to the story. This assumption was confirmed when KNKT investigators observed a UPRT session at Sriwijaya Air. When they sat in on a “nose low recovery” scenario, one of the first things they noticed was that Sriwijaya Air had made questionable modifications to the required callouts. The manufacturer’s procedures for dealing with a nose low upset — defined as a pitch angle of -10 degrees or lower — called for the non-flying pilot to announce “nose low” and suggest corrective actions. For unclear reasons, Sriwijaya Air had renamed the nose low upset to “Upset Brown,” presumably referring to the color of the primary flight display during such an upset, and bizarrely called for the non-flying pilot to make a mayday call to air traffic control before assisting in the recovery.

During the actual training session, more problems were observed. The instructor’s briefing failed to explain why certain steps were required, and failed to mention that the bank angle must be less than 60 degrees before attempting to recover in pitch. Common crew errors, and strategies to avoid them, were not discussed. And a video on upset recovery described in the syllabus was never shown.

Once the simulation began, the performance of the trainees was poor. During one nose low, high bank angle scenario, the trainee pilot attempted to level the nose before leveling the wings, resulting in an accelerated stall. Recovery from the accelerated stall was only accomplished at the urging of the instructor. And during a second run of the same scenario, the trainee pilot allowed the aircraft to enter an overspeed condition, which again required instructor intervention before it could be corrected. The overall takeaway was that neither the instructors nor the students understood what UPRT was for, why it was important, or how to perform the recovery maneuvers correctly. It was no wonder, then, that Captain Afwan failed to recover from the upset on board flight 182 — applying the incoherent training scenarios to an already below-average pilot was simply a recipe for disaster.

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Recovery workers transport a body off one of the salvage ships. (Reuters)

In the end, the KNKT pointed the finger squarely at the airline for both the mechanical and human failures which led to the crash. The company’s inadequate maintenance practices, lack of emphasis on incident reporting, and poorly trained engineers allowed a recurrent problem to persist for seven years, and its shoddy pilot training left many crews unprepared to deal with even the most minor in-flight upsets. If anything, it was a miracle that the airline had operated so long without a major accident.

It is worth stopping to note that Sriwijaya Air flight 182 was the only fatal crash of a passenger jet anywhere in the world in 2021. Most of the world has managed to rack up impressive safety records in recent years, but Indonesia continues to experience a major loss of a passenger jet approximately every two years, of which Sriwijaya Air flight 182 is merely the latest. To make matters worse, many of these crashes are quite similar: a manageable or even trivial mechanical problem occurs, the pilots allow it to escalate until they find themselves in an upset situation, and then they panic and fly their plane into the sea. Every time, the KNKT conducts a fairly decent investigation, recommendations are issued, and the DGCA vows reforms — but nothing actually changes. So why should we believe this time is different? The only real answer is that we shouldn’t.

Another body is removed from the scene. (Republika)

The initial reaction of the DGCA to the crash of flight 182 was the same as always — to put on a show for the public, by ordering arbitrary inspections of an arbitrary set of airplanes without knowing why the plane crashed, and without telling inspectors to look for anything in particular. These inspections are blatant security theater and are only performed because the DGCA is either unwilling or unable to take more substantive actions. On paper, at least, some changes were made — a DGCA task force was established to ensure that airlines were properly implementing their upset recovery training programs, and Sriwijaya Air made a number of reforms, from overhauling its UPRT program to improving troubleshooting training for engineers. Boeing also announced a pending service bulletin, expected to be backed by a binding airworthiness directive, which would mandate recurrent inspections of the spoiler position sensors on Boeing 737 Classic series airplanes. But in the end, signs of a systemic overhaul of the regulatory system in Indonesia remain largely absent.

Relatives of victims spread flowers at the crash site in the Thousand Islands. (AP)

As I’ve discussed in previous articles, the problem in Indonesia is not really a lack of rules — on paper, its safety regulations are not much different from those in any other country. The issue is a pervasive lack of enforcement and a sense of impunity among airline executives, who often enjoy broad political connections. After so many crashes caused by the same set of factors at one dysfunctional airline after another, one gets the sense that nobody, from the executives to the pilots to the DGCA inspectors, really knows what they’re doing, and that the ones who do are probably being bribed to pretend that they don’t. The result is Sriwijaya Air, an airline which in any functioning country would have been grounded when it split off from Garuda, but which, by virtue of being in Indonesia, is still flying today, even after a crash caused by rank incompetence at every level.

Although this article spends plenty of time diving into the details of what the automated systems were doing and what the pilots might have been thinking, it remains impossible to escape the fact that this was an accident which should never have been allowed to happen in 2021. We know how to prevent crashes like this, and have known for decades. We know how to train pilots who don’t lose control of perfectly controllable airplanes because they aren’t paying attention. We know how to spot recurrent mechanical defects and how to correct them. Sriwijaya Air just didn’t bother to learn. And if the DGCA can’t learn for them, then sometime in the next year or two another plane will go down in Indonesia, and I’ll be writing this same article again. If I’m not, then consider that a victory. In the meantime, however, a warning will suffice: if you must fly on a budget airline in Indonesia, beware — you might just get what you pay for.

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Admiral Cloudberg

Analyzer of plane crashes. Contact me via @Admiral_Cloudberg on Reddit, @KyraCloudy on Twitter, or by email at kyracloudy97@gmail.com.