SilkAir Flight 185

SilkAir Flight 185 was a scheduled SilkAir passenger flight operated by a Boeing 737-300 from Jakarta, Indonesia to Singapore that crashed into the Musi River near Palembang in southern Sumatra, on 19 December 1997, killing all 97 passengers and seven crew on board.[1]

SilkAir Flight 185
Parts of the wreckage of 9V-TRF, recovered from the Indonesian Musi River
Occurrence
Date19 December 1997
SummaryCause disputed:
SiteMusi River, Palembang, Indonesia
2°27′30″S 104°56′12″E
Aircraft
Aircraft typeBoeing 737-36N
OperatorSilkAir
Registration9V-TRF
Flight originSoekarno–Hatta Int'l Airport, Jakarta, Indonesia
DestinationSingapore Changi Airport, Singapore
Occupants104
Passengers97
Crew7
Fatalities104
Survivors0

The cause of the crash was independently investigated by two agencies in two countries: the United States National Transportation Safety Board (NTSB) and the Indonesian National Transportation Safety Committee (NTSC).[2] The NTSB, which had jurisdiction based on Boeing's manufacture of the aircraft in the United States, investigated the crash under lead investigator Greg Feith. Its investigation concluded that the crash was the result of deliberate flight control inputs, "most likely by the captain".[3][4] While the Indonesian NTSC investigators found that the there were "no concrete evidence" to support the pilot suicide allegation, and that the previously-suspected Parker-Hannifin hydraulic power control unit (PCU) had already been determined by the manufacturer to be defect-free, the final statement from the NTSC was that they were unable to determine a cause of the crash and thus inconclusive.[5]

Regardless of the findings, or lack thereof provided by the NTSB or NTSC, the potential factor of a defective Parker-Hannifin-made power control unit (PCU) that controlled the aircraft's rudder is still believed to have possibly led to the crash of the 737 aircraft. The cause of some previous 737 crashes, such as United Airlines Flight 585 and USAir Flight 427, had been attributed to the 737's rudder issues. Although the NTSB and PCU manufacturer Parker Hannifin had already determined that the PCU was properly working, and thus not the cause of the crash, a private and independent investigation into the crash for a civil lawsuit tried by jury in a state court in Los Angeles, which was not allowed to hear or consider the NTSB's and Parker Hannifin's conclusions, decided that the crash was caused by a defective servo valve inside the PCU, based on forensic findings from an electron microscope which determined that minute defects within the PCU had caused the rudder hard-over and a subsequent uncontrollable flight and crash.[5] The manufacturer of the aircraft's rudder controls and the families later reached an out-of-court settlement.[6]

Aircraft

The aircraft operating flight 185 was a Boeing 737-300 with manufacturer serial number 28556, registered as 9V-TRF and was powered by two CFM56-3B2 engines.[7] Having completed its maiden flight in January 1997, the aircraft was delivered to SilkAir in February 1997, 10 months before the crash.[8] At the time of the accident, it was the newest aircraft in SilkAir's fleet and had accumulated 2,238 flight hours in 1,306 cycles.[9][10] This is the first and only fatal hull loss for SilkAir.[3]

Accident

Carrying 97 passengers and a crew of seven, the Boeing 737 departed Jakarta's Soekarno-Hatta International Airport's runway 25R at 15:37 local time (08:37 UTC) for a planned 80-minute flight to Singapore Changi Airport, with captain Tsu Way Ming (朱卫民), 41, of Singapore, a former A-4 Skyhawk pilot, at the controls along with first officer Duncan Ward, 23, of New Zealand.[note 1][3][4] Generally fair weather was expected for the route, except for some thunderstorms near Singkep Island, 120 km (75 mi; 65 nmi) south of Singapore.[9]

The aircraft was cleared to climb to flight level 350 (FL350), about 35,000 ft (11,000 m), and to head directly to Palembang.[9] At 15:47:06, while climbing through 24,500 ft (7,468 m), the crew requested clearance to proceed directly to waypoint PARDI (0°34′S 104°13′E).[note 2][11] At 15:53, the crew reported reaching the cruise altitude of FL350 and was cleared to proceed directly to PARDI, and to report abeam Palembang. The cockpit voice recorder (CVR) ceased recording at 16:05. The TV series Mayday argues Captain Tsu may have taken the opportunity of leaving the cockpit for tripping the CVR circuit breaker in order to turn off the CVR.[5] At 16:10, the air traffic controller informed the flight that it was abeam Palembang and instructed the aircraft to maintain FL350 and to contact Singapore Control upon reaching PARDI. First Officer Ward acknowledged this call. At 16:11, nearly six minutes after the CVR ceased recording, the flight data recorder (FDR) also stopped recording. Mayday shows that Tsu is thought probably to have come up with an excuse to get Ward out of the cockpit. Having done so, the pilot then proceeded to lock his co-pilot out of the flight deck before disabling the data recorder; Tsu is presumed to have done this in order to ensure that there would be no record of what he was going to do next.[5]

Flight 185 remained level at FL350 until it started a rapid and nearly vertical dive around 16:12. While descending through 12,000 ft (3,700 m), parts of the aircraft, including a great extent of the tail section, started to separate from the aircraft's fuselage due to high forces arising from the nearly supersonic dive.[4] Seconds later, the aircraft impacted the Musi River, near Palembang, Sumatra, killing all 104 people on board. The time it took the aircraft to dive from cruise altitude to the river was less than one minute. The plane was travelling faster than the speed of sound for a few seconds before impact.[4] Parts of the wreckage were embedded 15 feet (4.6 m) into the riverbed.[12]

The aircraft broke into pieces before impact, with the debris spread over several kilometres, though most of the wreckage was concentrated in a single 60-metre (200 ft) by 80-metre (260 ft) area at the river bottom.[9] No complete body, body part or limb was found, as the entire aircraft and passengers disintegrated upon impact. Only six positive identifications were later obtained from the few recovered human remains.[3][9]

Passengers and crew

Silk Air issued a press release on 19 December 1997 with a passenger count by nationality,[10] and another the following day with crew details and a complete passenger manifest.[13]

Victims' nationalities
Nationality Passengers Crew Total
Singapore40646
Indonesia23-23
Malaysia10-10
United States5-5
France5-5
Germany4-4
United Kingdom3-3
Japan2-2
Bosnia and Herzegovina1-1
Austria1-1
India1-1
Taiwan1-1
Australia1-1
New Zealand-11
Total 97 7 104

Among those killed in the crash was Singaporean model and author Bonny Hicks.[14]

Investigation and final report

The accident was investigated by the Indonesian NTSC, which was assisted by expert groups from the US, Singapore, and Australia.

Around 73% of the wreckage (by weight) was recovered, partially reconstructed, and examined. Both of the aircraft recorders, the CVR (cockpit voice recorder) and the FDR (flight data recorder) were retrieved from the river and their data were extracted and analyzed.

The investigators tested 20 different simulations for various equipment failure scenarios, and found that the only scenario that matched the actual radar trajectory of the descent and crash of the flight was a high speed steep dive commanded by one of the pilots.[5][15] Furthermore, the investigators had found the trim jackscrew for the horizontal stabilizer, which revealed that flight inputs from one of the pilots had moved the stabilizer from level flight to a full nose down descent.[5][15]

It was initially speculated that first officer Duncan Ward had deliberately crashed the aircraft, as he was the only person in the cockpit when the CVR stopped recording. However, this was quickly ruled out, as Ward's friends, family and co-workers said that he had not displayed any signs of depression nor suicide during his career at SilkAir and was in a good mood on the morning of the accident flight.[5][9]

At 16:00, the CVR showed that Captain Tsu left the cockpit; five minutes later, the CVR stopped recording. Tests indicated that a click would be heard on the CVR recording if the CVR circuit breaker had tripped normally, but not if it had been pulled out manually. As there was no click, it is likely that Captain Tsu pulled out the CVR circuit breaker after leaving the cockpit. The NTSC and NTSB investigators thought that if Captain Tsu was responsible for the crash, he must have made up some excuse to get the First Officer to leave the flight deck before disabling the FDR (which would have immediately triggered a Master Caution on both pilots' control panels), so that his actions would not be noticed.[5] Several minutes later, as recorded by Indonesian ground radar, the aircraft entered a rapid descent, disintegrated, and crashed into the Musi River.

On 14 December 2000, after three years of investigation, the Indonesian NTSC issued its final report. The NTSC chairman overrode the findings of his investigators—that the crash was caused deliberately by pilot input—so that the report stated that the evidence was inconclusive and that the cause of the accident could not be determined:[9][note 3]

The US NTSB, which also participated in the investigation, concluded that the evidence was consistent with a deliberate manipulation of the flight controls, most likely by the captain.

In a letter to the NTSC dated 11 December 2000, the NTSB wrote:

The examination of all of the factual evidence is consistent with the conclusions that: 1) no airplane-related mechanical malfunctions or failures caused or contributed to the accident, and 2) the accident can be explained by intentional pilot action. Specifically, a) the accident airplane’s flight profile is consistent with sustained manual nose-down flight control inputs; b) the evidence suggests that the cockpit voice recorder (CVR) was intentionally disconnected; c) recovery of the airplane was possible but not attempted; and d) it is more likely that the nose-down flight control inputs were made by the captain than by the first officer.[15]

Geoffrey Thomas of The Sydney Morning Herald said that "a secret report confirmed that the Indonesian authorities would not issue a public verdict because they feared it would make their own people too frightened to fly."[16] Santoso Sayogo, an NTSC investigator who worked on the SilkAir 185 case, said that the NTSB opinion was shared by some Indonesian investigators, who were over-ruled by their boss.[5]

Potential motives

In the aftermath of the crash, several potential motives for the captain's alleged suicide and homicide were suggested, including recent financial losses of $1.2 million[12] (his share-trading showed trading of more than one million shares and his securities-trading privileges had been suspended 10 days before the accident due to nonpayment),[4] his obtaining a $600,000 life insurance policy the previous week which was to have gone into effect on the day of the accident[12] (though it later emerged that this was a routine policy taken out as part of a mortgage requirement),[4][17] his receipt of several recent disciplinary actions on the part of the airline (including one that related to improper manipulation of the CVR circuit breaker),[4] and the loss of four squadron mates during his military flight training, 18 years earlier on the exact date of the crash.[9] He had also had several conflicts with Ward and other co-pilots who had questioned his command suitability.[18] Investigations later revealed that his total assets were greater than his liabilities, although his liquid assets could not cover his immediate debts; his monthly income was less than his family's monthly expenditure; and he had some outstanding credit card debts.[4]

An official investigation by the Singapore Police Force into evidence of criminal offence leading to the crash found "no evidence that the pilot, copilot or any crew member had suicidal tendencies or a motive to deliberately cause the crash of [the aircraft]".[19]

Tsu was formerly a Republic of Singapore Air Force pilot and had over 20 years of flying experience in the older T/A-4S Skyhawks, as well as the newer T/A-4SU Super Skyhawks. His last appointment was instructor pilot of a Skyhawk squadron.

PA announcement

Captain Tsu made what appeared to be a routine public address announcement about the flight at 15:44:37, about 7 min after takeoff, which was recorded by the CVR and transcribed by the NTSC:[9][note 4]

Good afternoon ladies and gentlemen, this is your Captain. My name is Tsu Wai Ming. On the flight deck this afternoon with me is first officer Duncan Ward. We’d like to welcome you aboard and ah we are now climbing through nineteen thousand feet. We’ll be cruising today at thirty five thousand heading towards the north west tracking initially towards the eastern coast of Sumatra towards the town of Palembang before turning right towards Singapore. Flight time one hour twenty minutes. You can expect ah to arrive at Singapore at about six o’clock in the evening Singapore time which is one hour ahead of Jakarta time. Time in Singapore is now four forty five in the afternoon, this is about five minutes ahead of schedule. Weather conditions, clear skies out of Jakarta, very hot afternoon, and at the moment we are still in good weather, however toward Singapore we can expect a bit of showers, thunderstorm towards the southern part of Singapore. Arrival at Singapore should be fine with a temperature of about twenty eight degrees Celsius. The seatbelt sign is now off, feel free to move around the cabin, however while seated, for your own safety have your seatbelt fastened. Sit back and relax, enjoy the services provided today on SilkAir one eight five and I’ll get back to you just before our descent into Singapore with an updated weather forecast. Thank you.

Tsu's announcement ended at 15:46. At 16:05, 19 minutes later, the CVR stopped recording. Six minutes later, at 16:11, the FDR stopped recording, and at 16:12 the aircraft plunged into its fatal dive.

CVR and FDR deactivation

The cockpit voice recorder and flight data recorder stopped recording minutes before the abrupt descent, but not at the same time.[9] The CVR stopped functioning approximately 6 minutes before the dive as the captain was leaving the cockpit for a short break. The FDR was deactivated 5 minutes later approximately one minute before the dive. Overload and short circuit tests show that a distinctive 400-Hz tone is recorded by the CVR when the CVR circuit breaker trips. The investigators could not find this sound on Flight 185's CVR, which made them conclude that the CVR circuit breaker was manually pulled out. The radio continued to work after the failure of the CVR, which indicates that power failure was not the cause.[3][4] Subsequent investigations, including a National Geographic Channel documentary, revealed that this FDR had previously failed, for periods lasting between ten seconds and ten minutes. Testing of the unit by NTSC found no evidence that a malfunction or failure caused either recorder to stop recording data.[20]

Servo valve issue
Main article: Boeing 737 rudder issues

Starting in 1991, several accidents and incidents involving the Boeing 737 were the result of uncommanded movement of their rudders. On 3 March 1991, United Airlines Flight 585, a 737-200, crashed in Colorado Springs, Colorado, killing 25 people. On 8 September 1994, USAir Flight 427, a 737-300, crashed near Pittsburgh, Pennsylvania, killing 132 people. There were four more incidents where a 737 rudder power control unit (PCU) malfunction was suspected.

The Seattle Times devoted a series of 37 articles to Boeing 737 loss of control malfunctions.[21] The accident occurred in the middle of a controversy over the NTSB's role in accidents caused by the rudder control unit.[22]

During the investigation of Flight 427, the NTSB discovered that the PCU's dual servo valve could jam, as well, and deflect the rudder in the opposite direction of the pilots' input, due to thermal shock, caused when cold PCUs are injected with hot hydraulic fluid. As a result of this finding, the Federal Aviation Administration (FAA) ordered the servo valves to be replaced and new training protocol for pilots to handle unexpected movement of flight controls to be developed.[23] The FAA ordered an upgrade of all Boeing 737 rudder control systems by 12 November 2002.[24]

According to the series Mayday, the rudder issue had been corrected before construction started on the accident aircraft. Nevertheless, the theory of a rudder malfunction was investigated with the possibility of corrosion of and/or debris getting stuck in the power control unit, and was disproved.[5]

Aftermath

Lawsuits

SilkAir paid US$10,000 compensation to each victim's family, the maximum under the Warsaw Convention. Boeing also paid an undisclosed amount of compensation.[25] In 2001, six families who had sued SilkAir for damages based on the allegation that the crash was caused by the pilot were turned down by a Singapore High Court judge, who ruled that "the onus of proving that flight MI185 was intentionally crashed has not been discharged."[4]

Despite the fact that the NTSB and Parker Hannifin had already ruled out the possibility of mechanical failure as a cause to the crash of Flight 185 due to a defective PCU servo valve-unit (manufactured by Parker Hannifin), an independent and private investigation refocused on and further examined the recovered PCU device whose malfunctioning has been pointed out in other sudden Boeing 737 crashes. The manufacturer's records relating to this particular unit revealed that it had failed some routine tests, but they claimed to have corrected these problems. A metals expert, with the use of images from a scanning electron microscope, concluded that the servo valve had 'chip-outs' and numerous burrs "that could easily have interfered with the smooth operation of the valve".[26] After this investigation was complete, in 2004, a Los Angeles Superior Court jury in the United States, which was not allowed to hear or consider the NTSB's conclusions about the accident, found that the crash was caused by a defective servo valve in the plane's rudder.[26] The hydraulic PCU device manufacturer, Parker Hannifin, was ordered to pay the three families of victims involved in that case US$43.6 million.[25] After threatening to appeal the verdict, Parker Hannifin later compensated all families involved (although it did not accept liability).[4][6] Parker Hannafin spokesperson Lorrie Paul Crum stated that a federal law disallowed them from using the NTSB final report as evidence in the company's favour during the lawsuit. The lawyer representing the plaintiffs, Walter Lack, stated that the law only disallowed using the NTSB report's conclusion and suggestions, while statements of fact are admissible.[27]

SilkAir

In the aftermath of the crash, as well as with worsening conditions for Asian aviation in general due to the financial crisis, SilkAir terminated its Singapore–Jakarta service, and has not returned since. Before the crash, the route was served by both SilkAir and parent company Singapore Airlines; as of 2017, the route, the second-busiest international route in the world,[28] is served by Singapore Airlines and its budget offshoot Scoot, which combined, serve Jakarta a combined 79 times weekly (up to 12 daily flights).

Dramatisation

The Discovery Channel Canada / National Geographic TV series Mayday (also called Air Crash Investigation or Air Disasters) dramatised the accident in a 2013 episode titled Pushed to the Limit (broadcast in some countries as Pilot Under Pressure).[5]

Singaporean singer JJ Lin 's 2013 song "Practice Love" (修煉愛情) from the album Stories Untold (因你而在) is based on this accident,[29] as a close friend of the artist was killed on the flight.[30]

See also

Footnotes
  1. Captain Tsu had logged a total of 7,173 flight hours, including 3,614 hours on the Boeing 737. First officer Ward had 2,501 flight hours, with 2,311 of them on the Boeing 737.
  2. ATC reporting point north of Palembang.
  3. TV series Air Crash Investigation, episode "Pushed to the Limit", stated about 3 minutes before the end.
  4. Minor punctuation and typos have been fixed, refer to original transcript in Appendix A, p. A-12 of official NTSC report, or page 32 of the full CVR transcript by the NTSB.

References
  1. Sinha, Shreeya (26 March 2015). "A History of Crashes Caused by Pilots' Intentional Acts". The New York Times. Archived from the original on 18 April 2015. Retrieved 18 April 2015. A Boeing 737 belonging to the Singapore-based airline SilkAir was cruising at 35,000 feet in clear weather when it suddenly dove into a mangrove swamp near Palembang, Indonesia, on Dec. 19, 1997, killing all 104 people on board. Indonesian investigators said, that in the last seconds of the flight, there were indications that the pilot, Tsu Way Ming, "was in the process of, or intending to, leave the cockpit". He had recently been demoted and disciplined by the airline, and had large gambling debts. The government of Indonesia has yet to officially accept the findings.
  2. "SilkAir Flight 185: Controversial Crash". AviationKnowledge. Archived from the original on 3 December 2012. Retrieved 19 December 2012.
  3. Accident description at the Aviation Safety Network
  4. Job, Macarthur. "Final Flight: SilkAir." Flight Safety Australia. January–February 2008. Archived 27 February 2009 at the Wayback Machine
  5. "Pushed to the Limit". Mayday. Season 12. 2012. Discovery Channel Canada/National Geographic Channel.
  6. "SilkAir crash families finally receive answers with court verdict", Channel NewsAsia, 15 July 2004.
  7. "Accident information: Boeing 737 Silkair 9V-TRF". airfleets.net. Archived from the original on 9 November 2013. Retrieved 9 November 2013.
  8. "9V-TRF SilkAir Boeing 737-36N – cn 28556 / ln 2851". planespotters.net. Archived from the original on 9 November 2013. Retrieved 9 November 2013.
  9. "Aircraft Accident Report SILKAIR FLIGHT MI 185 BOEING B737-300 9V-TRF MUSI RIVER, PALEMBANG, INDONESIA 19 DECEMBER 1997" (PDF). knkt.dephub.go.id. National Transportation Safety Committee. 14 December 2000. Archived from the original (PDF) on 10 January 2014. Retrieved 15 May 2019.
  10. Report No. 3, Friday 19 December 1997, 2145hrs (Singapore time), SilkAir.
  11. "Waypoint PARDI ID". fallingrain.com. Archived from the original on 2 November 2014. Retrieved 9 January 2014.
  12. Richard C. Paddock (5 September 2001). "A Jet Crash That Defies Resolution". Los Angeles Times. Archived from the original on 17 March 2015. Retrieved 7 January 2015.
  13. Report No. 7, Saturday 20 December 1997, 1100 hrs (Singapore time), SilkAir.
  14. "Grieving relatives recall SilkAir crash victims". CNN. 20 December 1997. Archived from the original on 15 September 2008.
  15. "Letter from NTSB Chairman Jim Hall to Professor O. Diran and comments on the NTSB Committee's Draft final report of the accident" (PDF). National Transportation Safety Board. 11 December 2000. Retrieved 26 September 2019.
  16. The pilot who wanted to die Archived 6 July 2011 at the Wayback Machine, article by Geoffrey Thomas in The Sydney Morning Herald, 7 October 1999. Retrieved 19 September 2012.
  17. National Geographic Channel, Air Crash Investigation, Episode 4: "Pushed to the Limit"
  18. Laurinda Keys, Suicide is possible cause of jet crash, officials say pilot had history of troublesome behavior Associated Press, 11 March 1998.
  19. Singapore Police Force, Investigation into the Police Report lodged on 25 August 1999 by the Singapore-Accredited Representative to the National Transportation Safety Committee, 14 December 2000. (from archive.org)
  20. Griffioen, Hans. Air Crash Investigations: Mechanical Failure or Suicide the crash of SilkAir Flight 185. Lulu. pp. 243–246. ISBN 9780557673063.
  21. "What is the status of the solution to the B-737 rudder design defect? Is the problem solved?". AirlineSafety.com. Archived from the original on 29 July 2012. Retrieved 19 December 2012.
  22. "Expert Panel May Have Key To Which 737S Are Most at Risk". The Seattle Times. Archived from the original on 28 September 2015. Retrieved 19 December 2012.
  23. "UNCONTROLLED DESCENT AND COLLISION WITH TERRAIN USAIR FLIGHT 427 BOEING 737-300, N513AU NEAR ALIQUIPPA, PENNSYLVANIA SEPTEMBER 8, 1994" (PDF). National Transportation Safety Board. 24 March 1999. NTSB/AAR-99/01. Archived (PDF) from the original on 14 October 2012. Retrieved 19 December 2012.
  24. "02-28111 Airworthiness Directives; Boeing Model 737 Series Airplanes". e-Regulations. Retrieved 19 December 2012.
  25. Olson, Walter. "NTSB says no defect, jury says $44 million". Overlawyered. Archived from the original on 13 April 2014. Retrieved 11 April 2014.
  26. Quek, Tracy (11 July 2004). "3 families got $75m. Now 29 others are going to court". The Straits Times.
  27. "SilkAir crash: US firm told to pay US$44m". Business Times. 9 July 2004. Retrieved 12 November 2019. NTSB reports can't be used as evidence at trial under federal law, Ms Crum said. Mr Lack said factual statements from NTSB reports can be used, while conclusions and recommendations are barred by the law.
  28. "60th Edition of IATA World Air Transport Statistics". Archived from the original on 4 February 2018. Retrieved 30 January 2018.
  29. "《谁是大歌神》第3期 20160320完整版: 林俊杰首曝二十年情感历程【浙江卫视官方超清1080P】苏有朋、宁静、薛之谦、黄国伦" ["Who is the big song God" No. 3 20160320 full version: Lin Junjie first exposed 20 years of emotional history [Zhejiang Satellite TV official ultra clear 1080P] Su Youpeng, quiet, Xue Zhiqian, Huang Guolun]. YouTube (in Chinese). 中国浙江卫视官方频道 China Zhejiang TV Official Channel 【欢迎订阅】. 20 March 2016. Retrieved 27 March 2016.
  30. "Stories from his heart: A decade on, JJ Lin finds his identity as a musician and is ready to share of himself on a deeper level". Straits Times. 18 July 2013. Archived from the original on 18 August 2016. Retrieved 9 August 2016.

Further reading
(in Chinese)
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