Indonesia's conclusions on the SilkAir crash of December 1997 have done nothing to dispel the controversy over the incident
Andrzej Jeziorski/SINGAPORE
The Indonesian National Transportation Safety Committee (NTSC) has produced an evasive and worthless report on the crash of a SilkAir Boeing 737-300 on 19 December 1997, which killed 104 people. The investigation was always controversial, steeped in suggestions of pilot suicide, obscured by lack of evidence from the cockpit voice recorder (CVR) and flight data recorder (FDR), and further shrouded by the Indonesian investigators' reluctance to release data to the public.
In an interview with Flight International in 1999, NTSC chairman Oetarjo Diran said he was worried about making enemies for fear of undermining his plans to make the NTSC an internationally credible organisation to parallel the US National Transportation Safety Board (NTSB). In fact, Diran has achieved what he set out to avoid. The Committee has also plunged into direct conflict with the NTSB, which took part in the investigation.
Diran's summary of the report, issued on 14 December, says: "Due to the highly fragmented wreckage, and the nearly total lack of useful data, information and evidence, the NTSC has to conclude that the technical investigation has yielded no evidence to explain the cause of the accident."
The NTSB disputes this, citing "intentional pilot action" as the most probable cause, adding that the aircraft's descent profile was consistent with manual nose-down control inputs. In a letter to Diran, NTSB chairman Jim Hall writes: "Please note that our review of the draft final report revealed that several sections require correction, clarification, or the inclusion of additional information." He expresses "greatest concern" over the NTSC's inability to explain the aircraft's departure from level flight, and its recommendations "that are not supported by the factual evidence".
Diran contends that the suicide theory is a "plausible hypothesis", but "based on insufficient evidence". He adds: "The object of this investigation has to go beyond hypothesising to establish conclusions based on concrete evidence and proof." Diran appears to have made another mistake he set out to avoid: that of treating this inquiry as if it were a court of law with the task of establishing guilt or innocence, and the "prosecution" carrying the burden of proof.
Most probable cause
An accident inquiry is not concerned with prosecution, guilt, innocence or with absolute proof in the legal sense. Its mandate is to establish a "most probable cause", and make recommendations to reduce the risk of a similar accident in the future. The report does not attempt to reduce this risk.
None of the report's six recommendations addresses the suicide theory. Diran proposes a review of FDR/CVR design to "identify and rectify latent factors associated with stoppage-in flight", the fitting of underwater locator beacons to recorders, the recording of flight instrument displays, a review of flight crew training "to include recovery from high-speed flight upsets", the installation of flight envelope protection systems in all passenger aircraft, and the setting up of a regional framework for co-operation in accident investigation "to support those states that do not have the resources and facilities to do investigations on their own".
There is no recommendation on monitoring flight crews' psychological condition, despite the fact that the "plausible" suicide theory remains the most likely explanation. The investigators have suggested no coherent chain of events that could account for the "failure" of the CVR, then of the FDR six minutes later, the departure from level flight into a steep dive, the fact that the engines ran at high power all the way to impact two minutes later, the fact that no distress call was sent and that radar plots show no attempted recovery from the descent.
Simulations based on the five radar plots available yielded only one combination of control inputs that would take the aircraft through that descent profile. Initially, investigators agreed these inputs could only be explained by deliberate action, although Diran now says there is "no evidence", and that there could be "other permutations of inputs" that would produce the descent. He has not offered any of these for scrutiny. He does confirm, as was revealed in the mid-1999 interim report, that the aircraft's horizontal stabiliser trim at impact "corresponds with an aircraft nose down attitude".
The combination of systems and mechanical failures that might produce such a scenario by accident seems beyond reasonable probability. Add to this the pilot-in-command's chequered professional history, three recent disciplinary actions, his debts and multiple life insurance policies. These were detailed internally by the NTSC's human performance group in mid-1999, although Diran has said new information has since shown the pilot had positive net worth at the time of the accident, despite S$2.25 million ($1.3 million) in share losses. Diran has left out much of the new information, however, saying: "Specific details, such [as] the pilot's personal details, etc, were not deemed appropriate for inclusion in the final report."
Diran, as an engineer, says he has carried out this investigation by scientific principles. Perhaps he is familiar with the principle of Occam's Razor, which states that once one has eliminated the impossible, "one should not increase, beyond what is necessary, the number of entities required to explain anything".
Source: Flight International
