There is growing speculation that pilot suicide could have been responsible for the crash in December of a SilkAir Boeing 737-300 which nose-dived into the Musi River in Sumatra. As a result, the Indonesian-led investigation into the crash, in which 104 people died, has begun to focus attention on human performance factors.

A nine-man team of investigators has been formed to look specifically at human aspects involved in the accident, including the medical and financial background and past performance of the aircraft's crew. The group includes three psychiatrists and is made up of advisors from Indonesia, Singapore, Boeing and Australia's Bureau of Air Safety Investigation.

The captain of SilkAir flight MI185, 41-year-old former air force pilot Tsu Way Ming, has attracted interest from the media. Singaporean investigator Tam Wee Lee confirms that Tsu was withdrawn from line training duties a "couple of months" before the accident as the result of "some internal reports from fellow crews".

It is understood from airline sources that the reports include at least two from different New Zealand first officers relating to a go-around incident while landing in Sumatra and a later de-activation of a cockpit voice recorder (CVR). Flight MI185 was co-piloted by New Zealander Duncan Ward.

Chief investigator Professor Oetarjo Diran confirms that the CVR and flight data recorder (FDR) stopped working while the aircraft was flying normally at 35,000ft (10,700m). The CVR ceased recording "approximately 5-7min" before the FDR, which in turn stopped a "few minutes" before the aircraft began its rapid descent.

A US National Transportation Safety Board representative, Greg Feith, who is assisting the investigation, sought to play down the significance of both systems stopping in close succession, commenting: "I won't characterise it as unusual." Industry observers, however, have suggested that the chances of both independently powered recorders failing just before an accident are remote.

The last known pilot suicide involving a commercial airliner was the crash in 1994 of a Royal Air Maroc AI(R) ATR 42 which killed 44 passengers and crew.

Aside from manual circuit breaker de-activation of the CVR and FDR, investigators are examining other possible explanations, such as electrical failure, as well as corrosion, abrasion, or breakage of the system's wires. Feith says that a US metallurgist has been called in to examine bundles of wiring retrieved from the crash site, while a check will be made of an identically configured SilkAir 737-300.

Diran claims that the CVR has so far yielded no clues, and that the last 30s of the FDR's metallic tape has been corrupted by chemical pollutants in water that leaked into the box. He says that the team has found no evidence to support suggestions that one of crew left the cockpit shortly before the accident, but adds that the CVR is to be re-examined for unidentified sounds.

Source: Flight International