Investigation Summary
The investigation centered on the mysterious stoppage of the Cockpit Voice Recorder (CVR) at 16:05 and the Flight Data Recorder (FDR) at 16:11, followed by a sudden departure from level flight at 16:12. At 16:05, the CVR recorded the captain stating he was leaving the cockpit to fetch water; 13.6 seconds later, the recording ceased. Radar data showed the aircraft descending at a rate exceeding 30,000 feet per minute. Recovery of the horizontal stabilizer's trim jackscrew indicated that the aircraft had been trimmed to a full nose-down position. The NTSB argued that the lack of a 'click' on the CVR recording suggested the circuit breaker was manually pulled rather than tripping due to a fault. They also highlighted the captain's recent financial difficulties and professional setbacks as potential motives. However, a 2004 civil trial in California involving families of the victims resulted in a jury verdict blaming a defective servo valve in the rudder's Power Control Unit (PCU), a component that had caused other Boeing 737 accidents, though this was never accepted by the NTSB or Boeing as the cause for Flight 185.
Final Conclusions
The NTSC Final Report (14 December 2000) stated that the technical investigation yielded no evidence to explain the cause of the accident. The NTSB's formal rebuttal (11 December 2000) concluded that the flight profile was consistent with sustained manual nose-down inputs and that the recorders were likely intentionally disconnected by the captain.
Photographic Evidence (1)
Video Analysis
Two SilkAir Flights Crash 7 Years Apart in Similar ... — On December 19, 1997, SilkAir Flight 185 plunged headlong into the Musi River, near Sumatra, claiming the lives of everyone on board.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Systems & Failure Modes
Power Control Unit (PCU)
A hydraulic unit that controls the rudder. Plaintiffs in civil litigation alleged a defect in the PCU caused an uncommanded rudder hardover, though investigators found no evidence of this.
Flight Data Recorder (FDR)
The device stopped recording at 16:11:27, approximately one minute before the dive began, without any recorded system failures.
Horizontal Stabilizer Jackscrew
A mechanical screw that sets the pitch trim of the aircraft; it was recovered and showed the aircraft was trimmed for a steep dive.
Interesting Facts
- 01The aircraft was a nearly new Boeing 737-300, delivered less than a year before the accident.
- 02The descent was so rapid that the aircraft exceeded the speed of sound before impact.
- 03Approximately 73% of the wreckage by weight was recovered from the riverbed.
- 04The horizontal stabilizer jackscrew was found in a position corresponding to a full nose-down command.
- 05The NTSC chairman overrode his own investigators' findings of pilot suicide to issue an 'undetermined' final report.
- 06The crash occurred on the exact anniversary of a 1979 training mission where the captain's squadron mates were killed; he had missed that flight due to a mechanical issue.
Safety Actions & Advisories
Enhanced CVR/FDR Requirements
The investigation highlighted the vulnerability of flight recorders to manual disconnection, leading to discussions regarding independent power sources for recorders.
Known Controversies & Unanswered Questions
Dispute between NTSC and NTSB
Reference ↗The Indonesian NTSC officially ruled the cause as 'undetermined' due to lack of evidence, while the US NTSB formally stated the crash was caused by intentional pilot action.
Mechanical Defect vs. Pilot Suicide
Reference ↗A US civil jury in 2004 found that a defective rudder PCU caused the crash, contradicting the NTSB's pilot suicide conclusion.