The wreckage of the plane was reconstructed as part of the probe

Investigators from Taiwan's Aviation Safety Council said that the key focus of their enquiry was an aluminium patch which was used to fix an area by the rear cargo door, damaged in 1980.

"We have found... what we call multiple site fatigue cracks... with the length of nearly 70 inches (177cm)," said investigator Kay Yong.

Most people in Taiwan would prefer to travel on other airlines with better safety records David Learmount, Flight International magazine

The patch seems to have caused cracks and corrosion on the aeroplane's hull, although the investigators stress that they have not established that this definitely caused the crash.

"It does look like a highly inadvisable piece of engineering," said David Learmount of Flight International magazine.

"Either that, or the hull was not inspected fully for a pattern of progressive cracking, which caused the plane to disintegrate in mid-air," he told BBC News Online.

"The fact that either of these occurred speaks for itself when reflecting on China Airlines safety record, which is exceptionally bad when compared to other oriental airlines," he said.

The final investigation report will be released next year

Three China Airlines planes crashed in six years in the 1990s, killing more than 450 people.

After a crash in 1998 which killed 204 people, it had seemed that China Airlines had improved its safety record.

President Chen Shui-bian fired the state-owned company's top managers and hired a new chief executive, Christine Tsai-yi Tsung, to shake up the corporate culture.

The airline's previously poor safety record was blamed on a hidebound pilot culture, strongly influenced by air force traditions.

Among the changes introduced by Ms Tsung were that fewer pilots with military backgrounds were to be recruited and more would be sent to the United States and Australia for training.

China Airlines State-owned, founded in 1959 Privatisation plans delayed by economic downturn Fleet of 56 planes, including 29 Boeing 747s Flies to 40 cities in 20 countries

Investigators of the 2002 crash have ruled out pilot error.

The plane was, however, relatively old, having been flying for 23 years.

The BBC's Jonathan Marcus says that keeping older aircraft flying is not a problem in itself.

But, he says, it clearly requires operators to maintain the highest levels of maintenance and to ensure that repair work is carried out to the standards recommended by the manufacturer.

Questions about maintenance standards at China Airlines are bound to be asked, said David Learmount.

In the meantime, confidence in China Airlines is set to remain low.

"After the 1998 crash we saw a mass boycott of China Airlines by the Taiwanese. It seems most people in Taiwan would prefer to travel on other airlines with better safety records," he said.