SilkAir Flight 185

SilkAir Flight 185

Occurrence
Date	December 19, 1997
Summary	Disputed
Site	Palembang, Indonesia
Aircraft type	Boeing 737-36N
Operator	SilkAir
Registration	9V-TRFdisaster
Flight origin	Soekarno-Hatta International Airport
Destination	Singapore Changi Airport
Passengers	97
Crew	7
Fatalities	104
Injuries	0
Survivors	0

SilkAir Flight 185, a Boeing 737-36N, registration 9V-TRF, was a scheduled passenger service from Jakarta, Indonesia to Singapore, which crashed on December 19, 1997 after suddenly plunging into the Musi River from its 35,000 feet cruise altitude, killing all 104 people on board.

The accident was remarkable in that the CVR and FDR stopped recording, at different times and for no apparent reason, minutes before the aircraft departed level flight.

The crash was investigated by various groups, with the lead investigators, the Indonesian NTSC, unable to determine the cause, while the U.S. NTSB concluded that the crash resulted from a deliberate act by a pilot, most likely the captain.

Accident sequence

SilkAir Flight MI 185 departed Jakarta's Soekarno-Hatta International Airport 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 flight controls. The flight was cleared to climb to FL350 (approximately 35,000 feet above mean sea level), and to head directly to Palembang. At 15:47 the aircraft climbed through FL245. The crew then requested a clearance to proceed directly to PARDI. At 15:53, the crew reported reaching FL350 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 and to contact Singapore Control upon reaching PARDI. The crew acknowledged this call. At 16:11:27 the FDR ceased recording. Flight 185 was level at FL350 until it started a rapid and nearly vertical descent, as shown on radar, around 16:12:18. The aircraft broke up in flight, crashing into the Musi River, near Palembang, Sumatra.

All 97 passengers and 7 cabin crew, including the Singaporean captain, Tsu Way Ming and the 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 60x80 meter 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.

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

Investigation and final report

The accident was investigated by the Indonesian National Transportation Safety Committee (NSTC), which was assisted by expert groups from the U.S., Singapore and Australia. Both "black boxes" — the Cockpit voice recorder (CVR) and Flight data recorder (FDR) — were successfully recovered from the wreckage, and their data was retrieved.

On December 14, 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, 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.

Aftermath

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.

The Indonesian NTSC was highly criticised for failing to find and state any accident cause. The American NTSB also conducted extensive testing using simulators and computer modeling, which contradicted the Indonesian authority. There was unprecedented criticism from American NTSB investigators, who are adamant the only way to achieve the flight profile that occurred immediately prior to impact, was "with sustained nose-down manual flight control input".

In the aftermath of the crash, several potential motives for 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 a life insurance policy the previous week (the policy commenced 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 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 discovered his assets were greater than his financial losses, although that was not a clear motive for suicide, it cannot be ruled out.

An official investigation by the Singapore Police Force into evidence of criminal offence leading to the crash found that there was no motive nor reason for any of the crew 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 A-4SU and TA-4SU Super SkyHawks. His last appointment was instructor pilot of a SkyHawk squadron. Due to his flying experience, it was also highly unlikely that the aircraft lost control or fell into a stall or spin, as he would have had the experience to overcome such stalls and spins. The American NTSB investigators found no mechanical malfunctions, and they concluded the accident could only be explained by intentional pilot action.

The circuit breakers for the cockpit voice recorder and flight data recorder were apparently tripped minutes before the abrupt descent, but not at the same time. A technical analysis of the trip recorded in the CVR and FDR of these circuit breakers was carried out by investigators and the evidence showed that the trips were consistent with being manually activated. The radio continued to work after the failure of the recorders, which indicates that power failure was not a cause, however there was no conclusive evidence whether this was the action of the pilot or otherwise. This flight data recorder was old and had several periods of malfunction during the last days. It was precisely this lack of conclusive evidence, because of the switched off data and voice recorders, that made the case against Tsu impossible to prove.

The Indonesian National Transportation Safety Committee, which led the investigation, was not able to find any conclusive cause and even several years after the fact, many conspiracy theories remain. Skeptics point to other difficult to explain accidents involving 737s which showed signs of quirky flight controls such as uncommanded rudder deflection, including USAir Flight 427 and United Airlines Flight 585. The pilot suicide theory and controversy is very similar to that of EgyptAir Flight 990.

B-737 rudder upgrade

The U.S. FAA has ordered an upgrade of all B-737 aircraft before November 12, 2008. All airlines must install a new rudder control system that includes new components such as an aft torque tube, hydraulic actuators, and associated control rods, and additional wiring throughout the airplane to support failure annunciation of the rudder control system in the flight deck. The system also must incorporate two separate inputs, each with an override mechanism, to two separate servo valves on the main rudder power control unit (PCU) and an input to the standby PCU that also will include an override mechanism.

There was no conclusion by any of the investigative agencies that the Flight 185 crash was related to a rudder malfunction.

See also

• List of accidents and incidents on commercial airliners
• Air safety
• EgyptAir Flight 990
• Boeing 737 rudder issues

External links

• "Grieving relatives recall Silk Air crash victims," CNN
• SilkAir Press Release
• Picture of the Silk Air Boeing 737-36N aircraft which crashed (From www.airliners.net)