Kay Yong from Taiwan's Aviation Safety Council explains the orientation of the pieces of the China Airlines flight CI611's fuselage. (AP file photo)

Fatigue cracks in a Chinese Boeing 747 that were never properly repaired probably caused the plane to crash in May 2002, killing all 225 people on board, Taiwan investigators say.

In its final crash report, Taiwan's Aviation Safety Council said the cracks most likely caused "structural failure" in the tail section of the plane.

It said the tail section of the China Airlines plane may have suffered cracks in 1980 when it hit the runway during a takeoff in Hong Kong.

In May 2002, the Boeing 747 broke apart in mid-air, shortly after takeoff and plunged into the sea near Taiwan's Penghu Islands. The crash was the Taiwan carrier's fourth fatal accident since 1994.

"The in-flight breakup of CI 611, as it approached its cruising altitude, was highly likely due to the structural failure" in the tail section of the fuselage, the investigators said.

The safety council ruled out bad weather, pilot error, a terrorist attack and other external causes.