China Airlines Flight 611 - Metal Fatigue

Metal Fatigue

The final investigation report found that the accident was the result of metal fatigue caused by inadequate maintenance after a previous incident.

The report indicated that on 7 February 1980, the aircraft used on the flight had a tailstrike accident while landing in Hong Kong. Part of the plane's tail was damaged in the incident. The aircraft was de-pressurized, ferried back to Taiwan on the same day, and a temporary repair done the day after. A more permanent repair was conducted by a team from China Airlines from 23 May through 26 May 1980. However, the permanent repair of the tail strike was not carried out in accordance with the Boeing Structural Repair Manual (SRM). The area of damaged skin in Section 46 was not removed (trimmed) and the repair doubler plate that was supposed to cover in excess of 30% of the damaged area did not extend beyond the entire damaged area enough to restore the overall structural strength.

Consequently, after repeated cycles of depressurization and pressurization during flight, the weakened hull gradually started to crack and finally broke open in mid-flight on 25 May 2002, exactly 22 years to the day after the faulty repair was made upon the damaged tail. An explosive decompression of the aircraft occurred once the crack opened up, causing the complete disintegration of the aircraft in mid-air. However, this was not the first time that a plane had crashed because of a faulty repair following a tailstrike. On 12 August 1985, 17 years before the Flight 611 crash and five years after the accident aircraft's repair, Japan Airlines Flight 123 had crashed when the tailfin was torn off and the hydraulic systems severed by explosive decompression, killing 520 of the 524 people on board the aircraft. That crash had been attributed to a faulty repair to the rear pressure bulkhead, which had been damaged in 1978 in a tailstrike incident. In both crashes, the faulty repair had been an incorrectly installed doubler plate.

China Airlines disputed much of the report, stating that investigators did not find the pieces of the aircraft that would prove the contents of the investigation report.

One piece of evidence of the metal fatigue is contained in pictures that were taken during a routine inspection of the plane years before the crash. The photos showed visible brown nicotine stains around the doubler plate. This nicotine was deposited by smoke from the cigarettes of people who were smoking about seven years before the disaster (smoking was allowed in a pressurized plane at that time). The doubler plate had a brown nicotine stain all the way around it that could have been detected visually by any of the engineers when they inspected the plane. The stain would have suggested that there might be a crack caused by metal fatigue behind the doubler plate, as the nicotine slowly seeped out due to pressure that built up when the plane reached its cruising altitude. The stains were apparently not noticed and no correction was made to the doubler plate, which caused the crash to happen.