Andrzej Jeziorski/SINGAPORE

Indonesian accident investigators say they have contacted police after formally confirming that a SilkAir Boeing 737-300 may have been deliberately crashed by one of the crew in December 1997, near Palembang, Sumatra.

All 104 passengers and crew on board the 737, which was operating flight MI185 from Jakarta to Singapore, were killed when the aircraft plummeted to the ground from its cruising altitude of 35,000ft (10,675m). Leaked information has long suggested an act of suicide by a financially stricken and mentally troubled pilot. The latest interim report from the Indonesian Air Accident Investigation Commission (AAIC), released with heavily restricted circulation on 25 August, is the first time the investigators, and subsequently SilkAir, have formally admitted that pilot suicide was a possible cause.

"Suicide is not the conclusion at this point, but it could be a cause," says SilkAir general manager Mak Swee Wah.

The AAIC report says: "Wreckage investigation and the flight data recorder [FDR] recordings indicate that at impact the horizontal stabiliser had a nose-down trim which was different from the last known trim setting for cruise flight at the stoppage of the FDR, which could indicate a manual input from the cockpit."

The FDR and the cockpit voice recorder (CVR) stopped working before the aircraft began its descent. The AAIC adds that it has taken into account reconstructions and simulations that, according to unconfirmed reports, show the descent trajectory could only have been flown deliberately.

SilkAir says the captain and first officer were "fit to fly-by the best standards in the industry", despite AAIC confirmation that the captain had been suffering serious financial problems and had three disciplinary counts against him in the months leading up to the crash.

Indonesia's communications minister Giri Hadihardjono has written to his Singaporean counterpart Yeo Cheow Tong, citing suspicions of "unlawful interference" contributing to the accident. The matter has been referred to the Indonesian police for further investigation, while the Singaporean Government has also passed the findings to its police.

While the details remain unconfirmed officially, Tsu is understood to have run up debts of about S$3 million ($1.8 million) and to have taken out several insurance policies totalling S$3.4 million.

SilkAir has revealed details of three disciplinary actions facing Tsu. On 3 March, 1997, Tsu executed a go-around after a failed approach to Manado, but failed to file the necessary report, triggering an internal company inquiry.

On 24 June 1997, Tsu was en route to Jakarta with the same first officer as on the Manado flight. SilkAir says that before take-off Tsu deactivated the CVR in an attempt to preserve a recording of a conversation with his co-pilot (CVRs typically work on half-hour loops). This led to Tsu's demotion from line instructor pilot to captain. On the fatal 19 December flight, the CVR and the FDR stopped working before the aircraft's descent.

On 20 November 1997, Tsu returned to his departure airfield with engine problems, but again failed to file the relevant documentation. "He was counselled verbally and in writing," says the airline.

According to SilkAir parent Singapore Airlines (SIA), SilkAir general manager Mak is to be replaced imminently by Paul Tan, SIA's general manager for the UK and Ireland. Mak will return to SIA as a divisional vice-president.

Source: Flight International