surplus1 - it is perhaps worth reminding the readers here of the situation at the time of the Silk Air crash so that they can form their own view.
The two universally agreed fatal rudder hard-over accidents that I am aware of are as follows:
3 Mar 91 United Airlines Flight 585, (737-200) Colorado Springs, 25 killed.
8 Aug 94, USAir Flight 427 (737-300) Pittsburgh, 132 killed.
Other generally-agreed non-fatal incidents are as follows:
11 Apr 94, Continental Airways Flight (737-300) over Gulf of Honduras, aircraft veered violently to the right and Capt Ray Miller had 18 minute fight to try and sort the problem - eventually he and his co-pilot landed the aircraft safely.
9 Jun 96, Eastwind Airlines Flight 517 (737-200) experienced loss of rudder control while on approach to Richmond, VA.
23 Feb 99, MetroJet Flight 2710 (737-200) experienced a slow deflection of the rudder to its blowdown limit while flying at 33,000 feet above Salisbury, Maryland.
There is no doubt that the FAA and NTSB response to these incidents was not their finest hour. Some have accused them of being unwilling to grasp the nettle because of the overwhelming damage that could have been done to Boeing, their own national commercial aircraft producer and also due to the ramifications of an unsafe verdict being attached to the aircraft type given the sheer number of 737s in service at the time. Rightly or wrongly, therefore, the NTSB were not widely seen as 'honest brokers' by everyone. In the midst of all this, however the NTSB conducted significant amounts of research into the problem. It was eventually discovered that given certain circumstances a potentially-catasrophic situation could arise. Specifically, when cold PCUs were injected with hot hydraulic fluid, the resulting thermal shock could cause the PCU's dual servo valve to jam and deflect the rudder in the opposite direction to the pilots' input. As a result the FAA mandated updated full implementation by 12 Nov 02 of a rudder upgrade to prevent further incidents, and there have been no further incidents related to this problem since that time that I am aware of.
It was during this period that the Silk Air 185 crash (19 Dec 1997) took place. Due to the location of the crash site, the Indonesian National Transportation Safety Committee (NTSC) were put in charge of the investigation. The American NTSB were also actively involved in the investigation due to the USA being the aircraft's manufacturer. They concluded that the evidence was consistent with a deliberate manipulation of the flight controls, most likely by the captain (Tsu Way Ming). 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."
Despite this, three days later on 14 Dec 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. Privately, however, they did say that they could not talk of pilot suicide for fear of creating a crisis in civil aviation confidence within their own borders.
In the aftermath of the crash, several potential motives for the captain's alleged suicide/murder were suggested, including recent financial losses (his share trading showed losses of more than $1 million and his securities trading privileges had been suspended 10 days before 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 three squadron mates during his military flight training, which occurred 18 years earlier on the exact date of the crash. He also reportedly had several conflicts with his co-pilot that day, 23 year-old Duncan Ward (a New Zealander), 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."
This is where it all became very complex. In 2001, six families who had sued Silk Air 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 185 was intentionally crashed has not been discharged." In 2004, a 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. After threatening to appeal the verdict, Parker Hannifin later decided to compensate all families involved (although it did not accept liability) for an undisclosed sum.
So what can we conclude from this? Personally, the circumstantial evidence is so overwhelming that suicide/murder is the only credible conclusion. The final nail in the coffin for me is the height at which the aircraft was flying at and therefore the recoverable nature of this accident. For all his other failings, which were numerous, Captain Tsu Way Ming was an experienced 'stick and rudder' man from the military and clearly had a skill set equal to that of Ray Miller (the Continental Airlines captain mentioned previously). It was well within the range of his abilities to make some sort of recovery attempts from a rudder hard-over, had it been experienced - the evidence is that he made no attempt whatsoever to do so.
Short of a tape recording saying, 'I am going to kill you with an axe, you worthless Kiwi fool, and then I will crash vertically into the ground', I am not sure what else you would be looking for. Even had such a recording existed, there would still be the conspiracy theorists arguing it was a fake put in place by the CIA etc. Sadly, in that part of the world, losing face is everything and people have the great ability to throw every sensible thought out the window rather than rationally follow the evidence trail. Given the range of evidence, I would say the balance of sensible opinion would be overwhelmingly in favour of a conclusion that blamed the Captain for murder and suicide.