On 25 May 2002, a China Airlines Boeing 747-200 broke up in mid air, over Penghu Island Taiwan, following structural failure as a result of an improper repair in 1980, which had not been detected by subsequent inspections.
This is an extract from the Aviation Occurrence Report published by the Aviation Safety Council (Taiwan):
"On May 25 2002, 1529 Taipei local time (Coordinated Universal Time, UTC 0729), China Airlines (CAL) Flight CI611, a Boeing 747-200 (bearing ROC Registration Number B-18255), crashed into the Taiwan Strait approximately 23 nautical miles northeast of Makung, Penghu Islands of Taiwan, Republic of China (ROC). Radar data indicated that the aircraft experienced an in-flight breakup at an altitude of 34,900 ft, before reached its cruising altitude of 35,000 feet. The aircraft was on a scheduled passenger flight from Chiang Kai-Shek (CKS) International Airport, Taipei, Taiwan, ROC to Chek Lap Kok International Airport, Hong Kong, China…
…the final report does not directly state the “Probable Causes and Contributing Factors”, rather, it will present the findings in three categories: Findings related to the probable causes of the accident, findings related to risks, and other relevant findings…
Findings Related to Probable Causes:
- Based on the recordings of CVR and FDR, radar data, the dado panel open-close positions, the wreckage distribution, and the wreckage examinations, the in-flight breakup of CI611, as it approached its cruising altitude, was highly likely due to the structural failure in the aft lower lobe section of the fuselage.
- In February 7 1980, the accident aircraft suffered a tail strike occurrence in Hong Kong. The aircraft was ferried back to Taiwan on the same day un-pressurized and a temporary repair was conducted the day after. A permanent repair was conducted on May 23 through 26, 1980.
- The permanent repair of the tail strike was not accomplished in accordance with the Boeing SRM, in that the area of damaged skin in Section 46 was not removed (trimmed) and the repair doubler did not extend sufficiently beyond the entire damaged area to restore the structural strength.
- Evidence of fatigue damage was found in the lower aft fuselage centered about STA 2100, between stringers S-48L and S-49L, under the repair doubler near its edge and outside the outer row of securing rivets. Multiple Site Damage (MSD), including a 15.1-inch through thickness main fatigue crack and some small fatigue cracks were confirmed. The 15.1-inch crack and most of the MSD cracks initiated from the scratching damage associated with the 1980 tail strike incident.
- Residual strength analysis indicated that the main fatigue crack in combination with the Multiple Site Damage (MSD) were of sufficient magnitude and distribution to facilitate the local linking of the fatigue cracks so as to produce a continuous crack within a two-bay region (40 inches). Analysis further indicated that during the application of normal operational loads the residual strength of the fuselage would be compromised with a continuous crack of 58 inches or longer length. Although the ASC could not determine the length of cracking prior to the accident flight, the ASC believes that the extent of hoop-wise fretting marks found on the doubler, and the regularly spaced marks and deformed cladding found on the fracture surface suggest that a continuous crack of at least 71 inches in length, a crack length considered long enough to cause structural separation of the fuselage, was present before the in-flight breakup of the aircraft.
- Maintenance inspection of B-18255 did not detect the ineffective 1980 structural repair and the fatigue cracks that were developing under the repair doubler. However, the time that the fatigue cracks propagated through the skin thickness could not be determined…"
For further information see the full Aviation Safety Council (Taiwan) Aviation Occurrence Report: In-Flight breakup over the Taiwan Strait, Notheast of Makung, Penghu Island, China Airlines Flight CI611, BOEING 747-200, B-18255, MAY 25, 2002 (34Mb)
See also FAA "Lessons Learned from Transport Airplane Accidents": China Airlines Flight CI611, Boeing Model 747, B-18255.