Silk Air Flight 185

SilkAir Flight 185, a Boeing 737-36N, registration 9V-TRF, was a scheduled passenger flight from Jakarta, Indonesia to Singapore, which crashed on 19 December 1997 into the Musi River after abruptly plunging from its 35,000-foot (10,668-m) cruise altitude, killing all 97 passengers and 7 crew on board.

The cockpit voice recorder and flight data recorder stopped recording, at different times and for no apparent reason, minutes before the aircraft departed level flight and entered a steep vertical dive.

The crash was investigated by various groups, with different results. The Indonesian National Transportation Safety Committee (NTSC), who were lead investigators, were unable to determine the cause, while the U.S. National Transportation Safety Board (NTSB) concluded that the crash resulted from an intentional act by a pilot, most likely the captain.

Flight history
The Boeing 737-300 operating as Flight MI 185 was the newest in SilkAir's fleet, delivered to the airline on 14 February 1997, ten months prior to the crash.

Carrying 97 passengers and a crew of seven, the Boeing 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 the captain at the controls. Generally fair weather was expected for the route, except for some thunderstorms near Singkep Island, 120 km south of Singapore.

The jetliner was cleared to climb to flight level 350 (approximately 35,000 feet/10,668 m) above mean sea level), and to head directly to Palembang. At 15:47 the aircraft climbed through FL245 (24,500 feet/7,468 m). The crew then requested a clearance to proceed directly to PARDI. At 15:53 the crew reported reaching its cruise altitude of FL350 (35,000 feet/10,668 m) and was cleared to proceed directly to PARDI, and to report abeam Palembang. At 16:05 the CVR ceased recording. At 16:10 the controller informed the flight that it was abeam Palembang. The controller instructed the aircraft to maintain FL350 (35,000 feet/10,668 m) and to contact Singapore Control upon reaching PARDI. The crew acknowledged this call. At 16:11:27 the FDR ceased recording.

Crash
Flight 185 remained level at FL350 (35,000 feet/10,668 m) until it started a rapid and nearly vertical dive, as shown on Jakarta radar, around 16:12:18. The aircraft broke up in flight, crashing into the Musi River, near Palembang, Sumatra.

All 104 people on board, including the 41-year-old Singaporean captain, Tsu Way Ming and the 23-year-old co-pilot, 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. There was not a complete body, body part or limb found, as the entire aircraft and passengers disintegrated upon impact. Only six positive identifications were later obtained from the few recovered human remains.

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

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

Investigation and final report
The accident was investigated by the Indonesian National Transportation Safety Committee (NTSC), which was assisted by expert groups from the U.S., Singapore and Australia.

Approximately 73% of the wreckage (by weight) was recovered, partially reconstructed and examined. Both "black boxes" — the Cockpit voice recorder (CVR) and Flight data recorder (FDR) — were successfully retrieved from the wreckage, and their data was extracted and analyzed.

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 cannot be determined:

The U.S. National Transportation Safety Board (NTSB), which also participated in the investigation, disagreed with the NTSC and concluded that the evidence was consistent with a deliberate manipulation of the flight controls, most likely by the captain, which put the aircraft into a vertical dive and caused it to crash. In a letter to the NTSC dated 11 December 2000 the NTSB wrote:

Lawsuits
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."

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, decided that the crash was caused by a defective servo valve in the plane's rudder resulting in a rudder hard-over. The rudder manufacturer, Parker Hannifin, was ordered to pay the three families of victims involved in that case US$44 million. The company appealed the verdict, and the case was later settled out of court for an undisclosed amount.

Criticism of NTSC
The National Transportation Safety Board (NTSB) and Flight International criticized the National Transportation Safety Committee (NTSC). Flight International called the NTSC report an "evasive and worthless report[...]" and the NTSB posted a lengthy critique of the NTSC report. The U.S. NTSB conducted extensive testing using simulators and computer modeling, which contradicted the Indonesian authority. There was unprecedented criticism from NTSB investigators, who were adamant the only way to achieve the flight profile that occurred immediately prior to impact, was "with sustained nose-down manual flight control input".

Potential motives
In the aftermath of the crash, several potential motives for Captain Tsu's alleged suicide/homicide were suggested, including recent financial losses (his securities trading privileges had been suspended ten days prior to the accident due to non-payment), his obtaining an insurance policy on his life the previous week (the policy was to have gone into effect on the day of the accident), 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), and his possible grieving over the loss of four squadron mates during his military flight training, which occurred years earlier on the exact date of the crash. He had also reportedly had several conflicts with Ward, and other co-pilots who had questioned his command suitability. 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.

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

Tsu was formerly a Republic of Singapore Air Force pilot and had over twenty 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. Due to his flying experience, it was considered highly unlikely that the aircraft lost control or fell into a stall or spin, as he would have had the experience to avoid or overcome such conditions. The U.S. NTSB investigators found no mechanical malfunctions, and they concluded the accident could only be explained by intentional pilot action.

PA announcement
Captain Tsu made what appeared to be a routine PA announcement about the flight at 15:44:37, about seven minutes after takeoff, which was recorded by the CVR and transcribed by the NTSC:

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 recorders, which indicates that power failure was not a cause.

Similar Incidents
The theory that the crash was caused by a defective servo valve in the plane's rudder, resulting in a rudder hard-over, has been compared to two other Boeing 737 crashes, United Airlines Flight 585 and US Air Flight 427.