SilkAir Flight 185

The controversy was immense as to the cause of the crash, which was investigated by two independent agencies. The Indonesian National Transportation Safety Committee (NTSC) led by Engineering Professor Oetarjo Diran stated in its report that it could not determine a cause of the crash due to inconclusive evidence.

The United States' National Transportation Safety Board (NTSB) also participated in the investigation, given that the mishap aircraft was built by Boeing in the United States. Led by NTSB lead investigator, Greg Feith concluded, from their interpretation of the absent black box data, that the crash was the result of deliberate flight control inputs, most likely by the captain.

Following an independent and private investigation into the crash, a jury under the Superior Court in Los Angeles, which was not allowed to hear or consider the NTSB conclusions, decided that the crash was caused by a prominent issue inherent in other 737 crashes: a defective servo valve inside the power control unit (PCU) which controls the aircraft's rudder, had been forensically examined by the NTSB and the manufacturer of the PCU, and passed as not defective, but was again examined under a scanning electron microscope by independent investigators who concluded that minute defects in the PCU had caused a rudder hard-over and a subsequent uncontrollable crash. The manufacturer of the aircraft's rudder controls and the families later reached an out-of-court settlement.

Flight 185 has the third-highest death toll of any aviation accident in Indonesia after Garuda Indonesia Flight 152 and Mandala Airlines Flight 091.

Flight history

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. Having completed its maiden flight in January 1997, the aircraft was delivered to SilkAir in February 1997, ten months before the crash. 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.

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 former A-4 Skyhawk pilot, captain Tsu Way Ming (朱卫民), at the controls. Generally fair weather was expected for the route, except for some thunderstorms near Singkep Island, 120 km (75 mi) south of Singapore.

The jetliner was cleared to climb to flight level 350 (FL350), about 35,000 ft (11,000 m), and to head directly to Palembang. 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 1][10] At 15:53, the crew reported reaching its cruise altitude of FL350 and was cleared to proceed directly to PARDI, and to report abeam Palembang. At 16:05, the cockpit voice recorder (CVR) ceased recording abruptly. According to the TV series Mayday, Captain Tsu took the opportunity of leaving the cockpit to trip the circuit breaker. 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 Duncan Ward acknowledged this call. At 16:11, nearly six minutes after the CVR ceased recording, the flight data recorder (FDR) ceased recording.

Crash

Flight 185 remained level at FL350 until it started a rapid and nearly vertical dive around 16:12. While plunging 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. Seconds later, the aircraft impacted the Musi River, near Palembang, Sumatra. 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.

All 104 people on board, including the 41-year-old Singaporean captain, Tsu Way Ming (朱卫民) and the 23-year-old copilot, New Zealander Duncan Ward, died in the crash.

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. Not a single 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.

Investigation and final report

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

Around 73% of the wreckage (by weight) was recovered, partially reconstructed, and examined. Both "black boxes" – the CVR and FDR – were successfully retrieved from the river and their data were extracted and analysed.

According to the Canadian television series Mayday, at 16:00, the CVR showed that Captain Tsu left the cockpit; five seconds later, the CVR stopped recording. Tests indicated that a click would clearly 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, Captain Tsu was speculated to have pulled out the CVR circuit breaker before leaving the cockpit. NTSC and NTSB investigators postulated that if Captain Tsu were responsible for the crash, he returned to his seat and then concocted a pretense for First Officer Ward to leave the cockpit before pulling the FDR circuit breaker which would have been noticed by Ward had he remained, as disconnection would have triggered warning lights on the console.[4] 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 intensive investigation, the Indonesian NTSC issued its final report, in which it concluded that the evidence was inconclusive and that the cause of the accident could not be determined:[8]

The NTSC has to conclude that the technical investigation has yielded no evidence as to the cause of the accident.

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.

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."[14] Santoso Sayogo, an NTSC investigator who worked on the SilkAir 185 case, said that the NTSB opinion was, in fact, shared by some Indonesian investigators, who were overruled by their boss.[4]

Potential motives

In the aftermath of the crash, several potential motives for the captain's alleged suicide/homicide were suggested, including recent financial losses (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),[3] his obtaining an insurance policy on his life the previous week which was to have gone into effect on the day of the accident (though it later emerged that this was a routine policy taken out as part of a mortgage requirement),[3][15] 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),[3] and his possible grieving over the loss of three squadron mates during his military flight training, which occurred 18 years earlier on the exact date of the crash.[8] He also reportedly had several conflicts with Ward and other copilots who had questioned his command suitability.[16] 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.[3]

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]."[17]

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:[8][18]

Good afternoon ladies and gentlemen, this is your Captain. My name is Tsu Way 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 northwest 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 4:45 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 28°C. 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 185 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. A technical analysis of the sound signature of a CVR circuit breaker trip, as recorded by the CVR, was carried out by investigators and the evidence showed that the CVR stoppage was consistent with being manually initiated. The radio continued to work after the failure of the CVR, which indicates that power failure was not the cause. Subsequent investigations, including a National Geographic Channel documentary, revealed that this particular FDR had failed on numerous occasions, for periods lasting between ten seconds and ten minutes. However, testing of the unit by NTSC found no evidence that a malfunction or failure caused either recorder to stop recording data.

Servo valve issue

Starting in 1991, a number of 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. The accident occurred in the middle of a serious controversy over NTSB role in accidents caused by the rudder control unit.

During the course of 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. The FAA ordered an upgrade of all Boeing 737 rudder control systems by 12 November 2002.

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.

Aftermath

Lawsuits

SilkAir paid US$100,000 compensation to each victim's family, the maximum under the Warsaw Convention. Boeing also paid an undisclosed amount of compensation. 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, "the onus of proving that flight MI185 was intentionally crashed has not been discharged."

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." 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, deliberated for four days before delivering its unanimous verdict that the crash was caused by a defective servo valve in the plane's rudder. The hydraulic PCU device manufacturer, Parker Hannifin, was ordered to pay the three families of victims involved in that case US$43.6 million. After threatening to appeal the verdict, Parker Hannifin later decided to compensate all families involved (although it did not accept liability).

Dramatization

The story of the crash was featured on the 12th season of the Canadian TV series Mayday. The episode is entitled "Pushed to the Limit".