Sriwijaya Air Flight 182 was a scheduled domestic passenger flight from Jakarta to Pontianak, Indonesia. Just four minutes after departing from Soekarno–Hatta International Airport on 9 January 2021, the Boeing 737-500 entered an upset and crashed into the Java Sea off the Thousand Islands, killing all 62 people on board. A search of the area recovered wreckage, human remains, and items of clothing. The flight data recorder was recovered on 12 January, and the data storage module of the cockpit voice recorder was recovered on 30 March. Flight 182 was the deadliest plane crash in 2021.
During the search, Indonesia's National Transportation Safety Committee (NTSC) used the available data from Flightradar24, and hypothesised that the plane's engines were still operating upon impact. It was known that the autothrottle on this aircraft had malfunctioned a few days earlier, and one line of investigation was whether this might have contributed to the accident.
A preliminary report released on 10 February 2021 suggested problems with the plane's autothrottle; the thrust lever for the left engine reduced thrust as the aircraft climbed, while the thrust lever for the right engine remained fixed. On 10 November 2022, the NTSC published the final report of the investigation, concluding that the crash had been caused by a combination of a faulty autothrottle, pilot error and inadequate training.
Background
Aircraft
The aircraft involved was a Boeing 737-524, registered as PK-CLC (c/n 27323, Line no.2616). It was equipped with two CFM International CFM56-3B1 engines. At the time of the accident, the aircraft had accumulated 62,983 hours and 40,383 cycles.
The aircraft was manufactured in 1994, and was delivered to Continental Airlines in May 1994 under the registration N27610. The aircraft was transferred to United Airlines in 2010 after Continental and United merged. It was sold to Sriwijaya Air in May 2012, the first of fifteen 737-500s received by Sriwijaya Air that year to replace their 737-200s. Sriwijaya Air named the aircraft Citra.
Between March and December 2020, the aircraft was stored at Surabaya Juanda International Airport due to reduced demand for air travel during the coronavirus pandemic. The Ministry of Transportation inspected the aircraft on 14 December 2020 and issued a new certificate of airworthiness three days later. It resumed service on 19 December 2020.
Passengers and crew
There were 62 people on board, of who 50 were revenue passengers (43 adults and 7 children). Of the 12 crew members, six were operating crew on the flight, while the other six were deadheading as passengers. The majority of the passengers were residents from West Kalimantan.
Among the passengers were Mulyadi Tamsir, a politician from the People's Conscience Party (Hanura) and chairman of the Indonesian Muslim Student Association.
The crew on the flight consisted of Captain Afwan, 54, who had over 17,904 hours of flight experience, including 9,023 hours on the Boeing 737, First Officer Diego Mamahit, 34, who had over 5,107 hours of flight experience, with 4,957 of them on the Boeing 737, and four flight attendants. Afwan was a former pilot in the Indonesian Air Force.
The six deadheading crew and several revenue passengers had transferred to Flight 182 from an earlier NAM Air flight that did not operate. (NAM Air is a subsidiary of Sriwijaya).
Flight timeline
Flight 182 was scheduled to depart from Soekarno–Hatta International Airport at 13:40 WIB (06:40 UTC), and to arrive at Supadio International Airport in Pontianak, West Kalimantan, at 15:00 WIB (08:00 UTC). Departure was delayed by monsoon rains, and Flight 182 took off from runway 25R at 14:36 local time (07:36 UTC). Due to the delay, it was expected to land in Pontianak at 15:50 WIB (08:50 UTC).
The aircraft departed on a standard instrument departure with a clearance to climb to 29,000 ft (8,800 m). After being instructed by the ATC to pause their ascent at 11,000 feet (3,400 m), Captain Afwan entered the revised altitude into the autopilot. To level the aircraft off, the autothrottle attempted to move the levers back. While the left lever moved backwards, the right lever remained stuck at climb power due to excessive friction in the throttle control cable.
The aircraft was in a right turn, with the autopilot using the ailerons and spoilers to bank the aircraft to the right. But as the left lever kept decreasing while the right lever was still at climb power, thrust asymmetry caused the aircraft to start turning (yawing and rolling) to the left. The autopilot tried to keep the right bank going by deflecting the control surfaces to their maximum extent, but the thrust asymmetry continued to increase until it overpowered the autopilot. In the space of 68 seconds the aircraft rolled from a bank angle of 20 degrees right wing down to wings level, and after a further 15 seconds it was banked 37 degrees to the left. The pilots apparently did not notice the change of the aircraft's bank angle. The pilots had a few minor distractions at this point - a standard checklist to follow at 10,000', levelling off at 11,000' and almost immediately being cleared to 13,000' - but none of these activities should have taken their attention away from the task of monitoring the aircraft's flight path using the electronic attitude indicator ("artificial horizon").
When the bank angle reached 37 degrees, the Bank Angle warning sounded, startling the pilots. Because the autopilot was still holding the control wheel to the right, Captain Afwan probably assumed they were overbanked to the right, and instinctively yanked the wheel back to the left and disengaged the autopilot. In fact, the aircraft was actually overbanked to the left because of the asymmetric thrust - which the pilots were still unaware of - and the autopilot was resisting that tendency. The captain's hasty action ran counter to his training, which taught that pilots should first assess the situation by reference to their instruments before deciding how to recover the aircraft.
When the autopilot was disconnected, the crew lost any protection it had been giving them, and with Captain Afwan's left turn input, the aircraft banked through its maximum allowable bank angle and rolled through 90 degrees to the left. The nose
dropped and the aircraft descended, inverted, towards the Java Sea. First Officer Mamahit shouted to Captain Afwan regarding the bank angle, warning him that the aircraft had entered an upset condition. Realizing his mistake, Captain Afwan pulled the yoke back and attempted to recover from the dive. Due to being inverted, his action led to an increased rate of descent, and the aircraft dropped by 10,000 ft (3,000 m) in less than a minute.
Captain Afwan managed to almost level the wings and pull the nose up to a nearly 0-degree angle, but by then there was no more room for recovery as the altitude was too low and the aircraft was in overspeed condition. The aircraft crashed belly-first into the Java Sea near Laki Island and 19 km (12 mi) from Soekarno–Hatta International Airport, less than five minutes after takeoff. There were no survivors. During its climb, Flight 182 went off course to the northwest. Air traffic control (ATC) asked the crew about the deviation and got no response. A few seconds later, the aircraft dropped off radar. There was no distress call during the flight.
Search and recovery
The crash site was located 11 nmi (20 km) from Soekarno-Hatta International Airport.
Personnel from a vessel provided by the Ministry of Transportation recovered body parts, fragments of clothing, electronics, personal belongings and wreckage from the sea near the Thousand Islands, with aviation fuel also reported around the location.
The National Search and Rescue Agency (Indonesian: BASARNAS) immediately deployed personnel to the crash site while the National Police and the Ministry of Transportation set up crisis centres in Port of Tanjung Priok and Soekarno–Hatta International Airport. The Indonesian Navy deployed a number of vessels for the search and rescue operations, in addition to helicopters and KOPASKA (frogman) personnel.
The Indonesian government requested assistance from the South Korean government with the search. Through the Korea - Indonesia Marine Technology Cooperation Research Center (MTCRC), the South Korean Ministry of Oceans and Fisheries deployed a research vessel equipped with a detector to Indonesia. At least 15 personnel from MTCRC were also sent. The Singaporean government also provided assistance in the search.
Rescuers recovered a life vest, pieces from the aircraft's fuselage, and a destroyed wheel rim from the Boeing 737. Most of the wreckage was found at a depth of 17–23 metres (56–75 ft).
On the night of 9 January, an emergency slide from the aircraft was recovered from the waters near Lancang Island, Thousand Islands. The scattered debris and the small pieces of the wreckage indicated a high-speed impact. Much more wreckage was found over the next few days.
The Indonesian Navy pinpointed the exact coordinates of the crash site on 10 January, and the flight data recorder was retrieved two days later. The casing of the cockpit voice recorder was recovered on 15 January but the data storage module inside was missing. The search for victims and aircraft debris continued until 21 January. A total of 122 pieces of debris were recovered from the crash site, including one of the engine turbines. The search for the data storage module of the CVR continued until it was dredged up from the seabed on 30 March.
Investigation
The NTSC was immediately notified of the accident, with assistance from BASARNAS. NTSC stated that starting on 10 January 2021, just before 06:00 local time, search and rescue personnel would start searching for the aircraft's flight recorders. It added that the investigation will be assisted by the United States' National Transportation Safety Board (NTSB), with the Singaporean Transport Safety Investigation Bureau also offering assistance with the investigation. On 10 January, NTSC obtained raw data of the aircraft's flight path from radar and interviews with the air traffic controller. Investigators also retrieved the transcript of communications between the pilots and ATC.
Weather data retrieved from the Meteorology, Climatology, and Geophysical Agency (BMKG) confirmed the presence of moderate to heavy rain during takeoff with chance of thunderstorms reported. The data later showed that a 15 km (9.3 mi) high cumulonimbus cloud was present around Soekarno-Hatta International Airport with the minimum temperature of the cloud tops at −70 °C (−94 °F), prompting speculation that the aircraft had encountered turbulence. Visibility was estimated to be between 6 km (3.7 mi) and 10 km (6.2 mi). Analysis by the Indonesian National Institute of Aeronautics and Space (LAPAN) showed that weather conditions were not extreme. LAPAN stated that a meso-convective system had been formed near the Java Sea at 11:00 WIB (04:00 UTC), but the system had already dissipated by the time Flight 182 took off. According to NTSC, there was no indication that there would be any significant cloud on the aircraft's flight route. NTSC confirmed, however, that the pilots had contacted Jakarta ATC to change its heading to 075 degrees due to bad weather.
An investigator with NTSC stated that based on the distribution of the debris, the aircraft possibly ruptured when it hit the water. Combining Flightradar24 data and the shape of the engine turbine's fan blade and turbine disc, NTSC speculated that the aircraft's engines were still operating upon impact; based on the evidence, the aircraft was still responsive at 250 feet (76 m).
There was a public concern that the aircraft was not airworthy. The Federal Aviation Administration initially had issued an Airworthiness Directive to Boeing 737-500 operators concerning fatigue cracking on the left nacelle support overwing fitting flange fastener hole. The director of Sriwijaya Air, Jefferson Irwin Jauwena, insisted that the aircraft was airworthy. Moreover, the Ministry of Transportation later examined the aircraft's airworthiness and determined that the aircraft was safe to fly.
An Indonesian aviation expert said that the aircraft had been stored for repairs by Sriwijaya Air between 23 March and 23 October 2020. However, other experts speculated that the long time spent inactive may have caused deterioration and that technical problems may have developed.
On 15 January 2021, NTSC announced that the data from the FDR have been successfully downloaded. A total of 330 parameters were being examined and analysed by investigators. A Reuters report said that the data extracted, such as flight path, speed and engine condition, were "in good condition."
The preliminary report was released on 10 February 2021.
Data from the CVR was downloaded and included the accident flight, although it transpired that the captain's microphone was not recorded and the cockpit area microphone was all but inaudible due to interference.