Signs of fatigue discovered in China Airlines wreckage

Investigators examining wreckage from China Airlines Flight 611, which flew apart 35,000 feet over the Taiwan Strait, have discovered fatigue cracks in the rear fuselage near a 22-year-old repair, sources close to the investigation said.

The Boeing 747-200 suddenly broke up on May 25 about 20 minutes after taking off from Taipei for Hong Kong, killing all 225 people aboard. There was no distress call, and so far the plane's cockpit-voice recording and flight-data recording have revealed no definitive cause for the rare high-altitude disintegration.

The fatigue cracks are the first physical evidence pointing to a possible cause, and investigative sources said that area of the fuselage "is getting a lot of attention." But the sources stressed that much work remains before Taiwan's Aviation Safety Council can determine whether the fatigue cracks played a role in the crash or some other event caused the fuselage to crack apart.

The cracks raise two questions for investigators: First, were they the initiating event in the crash? And second, are the cracks a one-time defect caused by a repair, or should all older 747s be inspected for cracks?

So far, several sources said, the cracks appear to be a one-time event, but not enough wreckage has been recovered from the ocean floor to make a final determination. Salvage operations continue.

The in-flight breakup does not appear to have been the result of an explosion or fire. Officials have said they do not see any telltale burns or blast damage. Nor does it appear to have been from a fuel-tank explosion.

A fatigue crack in metal grows over time, sometimes because of damage or flexing.

The cracks found in the rear fuselage of the China Airlines plane, at least one of which was 40 inches long, were all near a 2-foot-by-10-foot "doubler," a metal patch used to repair damage caused in 1980 by a "tail strike." In a tail strike, the fuselage rubs the runway, usually when an airplane takes off too steeply.

The Taiwanese investigative agency is only now getting maintenance paperwork that will tell who performed the repairs and exactly what was done.

Fatigue cracks in older aircraft are not a new issue. The Federal Aviation Administration initiated an aging-aircraft inspection program after part of the roof tore off of an older Aloha Airlines Boeing 737 in April 1988. The National Transportation Safety Board found that Aloha had failed to inspect the aircraft adequately for cracks.