Andrzej Jeziorski/SINGAPORE

Twelve months after the crash of a SilkAir Boeing 737-300 on 19 December 1997, officials investigating the accident admit that "human factors" are the only avenue of investigation which remains open.

But they add that it is difficult to assess accurately the state of mind of the captain, Tsu Way Ming. Numerous media reports have suggested suicide as a possible cause of the crash.

At the same time, lawyers from the Nolan Law Group, acting on behalf of some of the victims' families, have begun a new push for the release of details, saying the investigators' unwillingness to allow disclosure "is now obstructing and infringing upon the rights of the next-of-kin to move forward on their claims for compensation".

Families of the victims attended a three-and-a-half-hour briefing by chief investigator Oetario Diran of the Indonesian Air Accidents Investigation Commission on 18 December. Sources close to the investigation say many were deeply unhappy at the lack of new material presented on the crash, which killed all 104 passengers and crew.

Five of the victims' families have so far accepted a SilkAir offer of $75,000 compensation, while others are heeding lawyers' advice to await the final outcome of the investigation.

Work has focused on two possible explanations for the aircraft's 35,000ft supersonic dive into Sumatra's Musi River - mechanical failure and pilot suicide. However, severe damage to the airframe and difficulties in researching the pilot's background have led Diran to admit that the final report may be inconclusive. No breakthroughs are expected from mechanical test reports still under study.

In an interview with Flight International's sister on-line service Air Transport Intelligence, Diran says Singaporean privacy laws have hampered investigations into the pilot's finances. No evidence has been obtained so far to support allegations that Tsu had taken out a multi-million-dollar life insurance policy just before the crash, and that he was heavily in debt. Financial records are hard to access without court approval.

"If necessary, we will go to court," says Diran. He points out that it is difficult to prove whether technical failure was a factor because the aircraft was "literally pulverised". The force of the crash had driven some wreckage 9m (30ft) into the mud.

Some lawyers representing victims' relatives have argued that traces of chemical contamination found in the flight data recorder (FDR) could have been caused by a chemical leak from the aircraft's toilet, triggering an uncommanded rudder hardover. But Diran says the contamination is likely to have come from chemical plants upstream of the crash.

Both the FDR and the cockpit voice recorder stopped working minutes before the aircraft dived, triggering suggestions that Tsu may have switched them off before precipitating the final manoeuvre.

Although there is no formal time limit on the investigation, Diran says that it cannot go on for much longer.

Source: Flight International