Investigators examine the cockpit section of a crashed China Airlines Boeing 747 in this 2002 file photo. (AirDisaster.Com Archives)

After a near 3-year long investigation, Taiwan's Aviation Safety Council (ASC) issued its final report on Friday on the Boeing 747-200 that disintegrated in mid-air and plunged into the sea near Taiwan's Penghu islands on May 25, 2002.

The 23-year-old aircraft had been on its way to Hong Kong and the crash was the Taiwan carrier's fourth fatal accident since 1994.

"A continuous crack of at least 71 inches (180 cm) in length, a crack length considered long enough to cause structural separation of the fuselage, was present before the inflight break-up of the aircraft," said the ASC in the report.

"The ASC concludes that the inflight break-up of the CI611, as it approached its cruising altitude, was highly likely due to the structural failure in the aft lower lobe of the fuselage."

The ASC said the crack on the back half of the fuselage was caused in a tail strike incident in 1980, and China Airlines had failed to repair the crack in accordance with Boeing Co.'s maintainence procedures.

It said the strength of a fuselage would be compromised with a continuous crack of 58 inches or longer.

"From the report it's clear the aircraft was poorly repaired and maintained and the negligence took away 225 human lives," said Victor Huang, whose wife was one of the plane's 19 crew.

"They should take responsibility. We deserve justice," said Huang, one of 92 relatives who have refused to settle with China Airlines, which offered each victim T$14.2 million (US$455,000) in compensation.

METAL FATIGUE

Investigators also found poor communications between China Airlines and Boeing about how to repair the damage after the 1980 incident, and urged Boeing to take a more pro-active approach in its field service.

Metal fatigue cracks that penetrated the skin of the aircraft -- as well as signs of metal corrosion -- had been covered by a patch called a "repair doubler", which was added as reinforcement to the plane after its tail struck a runway in Hong Kong.

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China Airlines said the available information was not conclusive enough to determine the exact cause of the accident and disagreed with part of the official finding.

"Now it seems the repair work might not be thorough, but that was the practice of many companies at that time. We did follow Boeing's procedures," said Roger Han, a spokesman for China Airlines.

The ASC said its finding was based on data collected from 1,500 pieces of wreckage, or about 75 percent of the whole structure recovered.

Since 1997, the aging plane had had a total of 29 delayed or overdue inspections, which were supposed to prevent corrosion or deterioration of parts, the report said.

"The aircraft had been operated with unresolved safety deficiencies from November 1997 onward," the ASC said.

The China airlines crash spurred the U.S. Federal Aviation Administration (FAA) to require U.S. airlines flying 747s to report if they had placed covers over repaired cracks or scratches on the underside of aircraft near the tail.