CI611 Occurrence Investigation Report
After 2 years and 9 months since its occurrence, the Aviation Safety Council (ASC) today releases the CI611 occurrence investigation report.
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). The aircraft was on a scheduled passenger flight from Chiang -Kai-Sheik (CKS) International Airport, Taipei, Taiwan, to Chek Lap Kok International Airport, Hong Kong, China. All 206 passengers and 19 crewmembers sustained fatal injuries.
The Aviation Safety Council (ASC) immediately launched a team to conduct the investigation of this occurrence. National Transportation Safety Board (NTSB) of U.S.A. is the Accredited Representative of the manufacture, which included its team members FAA, the Boeing Commercial Airplane Company, and Pratt & Whitney. Other teams invited to this investigation consisted members from the Civil Aeronautical Administration (CAA) of ROC, and the operator China Airlines.
The final report was approved by the 75th Council meeting on February 1, 2005 and published on February 25,2005.This report follows the format of ICAO Annex 13 with a few minor modifications. In order to further emphasize that the purpose of the investigation report is to enhance aviation safety, and not to apportion blame or liability, the final report does not directly state the “Probable Causes and Contributing Factors”, rather, it presents the findings in three categories: Findings related to the probable causes, findings related to risks, and other relevant findings. The Safety Council also includes the safety actions already taken or planned by the stakeholders. The Safety Council decided that this modification would better serve its purpose for the improvement of aviation safety.
There are 6 finding related to the 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 ASC concludes that 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.
‧ The ASC found evidence of fatigue damage 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.
‧ Residual strength analysis indicated that the main fatigue crack in combination with the 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. Although the ASC could not determine the length of cracking prior to the accident flight, the Council 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.
‧ The ASC found that the 15.1-inch crack and most of the MSD cracks initiated from the scratching damage associated with the 1980 tail strike incident in Hong Kong, which the repair was not accomplished in accordance with the Boeing SRM, as the damaged skin in that area was not removed (trimmed) and the repair doubler did not extend sufficiently beyond the entire damaged area to restore the structural strength.
‧ Prior to the occurrence, the operator’s maintenance inspection of B-18255 did not detect the ineffective 1980 structural repair and the fatigue cracks that were developing under the repair doubler.
On March 21, 2003, the Safety Council issued an Interim Flight Safety Bulletin strongly recommended that all civil aviation accident investigation agencies to collaborate with their regulatory authorities to take appropriate action of transport-category aircraft with pressure vessel repairs. The Council noted that an improperly treated scratch on the aircraft pressure vessel skin, especially if covered under a repair doubler, could be a hidden damage that might develop into fatigue crack eventually causing structure failure.
Other than findings related to probable causes, there are 7 findings related to risks, which identify elements of risk that have the potential to degrade aviation safety. The council believes that even though the risks findings may not be directly related to the occurrence, but from the standpoint of aviation safety, the ASC re-emphasizes that those risk findings are considered equally important as compared to the findings related to the probable causes.
The findings related to risks include:
‧ The first Corrosion Prevention and Control Program (CPCP) inspection of the accident aircraft was on November 1993 making the second CPCP inspection of the lower lobe fuselage due in November 1997. Reduced aircraft utilization led to the dates of the flight hour inspections being postponed, thus the corresponding CPCP inspection dates were passed. CAL’s oversight and surveillance programs did not detect the missed inspections.
‧ According to maintenance records, starting from November 1997, B-18255 had a total of 29 CPCP inspection items that were not accomplished in accordance with the CAL AMP and the Boeing 747 Aging Airplane Corrosion Prevention & Control Program. The aircraft had been operated with unresolved safety deficiencies from November 1997 onward.
‧ The CPCP scheduling deficiencies in the CAL maintenance inspection practices were not identified by the CAA audits.
‧ The determination of the implementation of the maximum flight cycles before the Repair Assessment Program was based primarily on fatigue testing of a production aircraft structure and did not take into account of variation in the standards of repair, maintenance, workmanship and follow-up inspections that exist among carriers.
‧ Examination of photographs of the item 640-repair doublers on the accident aircraft, which was taken in November 2001 during CAL’s structural patch survey for the Repair Assessment Program, revealed traces of staining on the aft lower lobe fuselage around STA 2100 were an indication of a possible hidden structural damage beneath the doublers.
‧ CAL did not accurately record some of the early maintenance activities before the accident, and the maintenance records were either incomplete or not found.
‧ The bilge area was not cleaned before the 1st structural inspection in the 1998 MPV. For safety purpose, the bilge area should be cleaned before inspection to ensure a closer examination of the area.
16 other findings could be found in the full report.
As the result of this investigation, the ASC issues a total of 21 safety recommendations to China Airlines, the CAA of ROC, the Boeing commercial Airplane Company, FAA/USA, the Ministry of National Defense and the Ministry of Justice.
Among the recommendations sent to CAL includes:
‧ CAL to perform structure repair according to the SRM or other regulatory agency approved methods, without deviation, and perform damage assessment in accordance with the approved regulations, procedures, and best practices
‧ Assess and implement safety related airworthiness requirements, such as the RAP, at the earliest practicable time.
‧ Review the self-audit inspection procedures to ensure that all mandatory requirements for continuing airworthiness, such as CPCP, are completed in accordance with the approved maintenance documents.
‧ Enhance record keeping and self-audit inspection procedures.
Safety recommendations to the CAA of ROC includes:
‧ Ensure that all safety-related service documentation relevant to ROC-registered aircraft is received and assessed by the carriers for safety of flight implications.
‧ Ensure that the process for determining implementation threshold for mandatory continuing airworthiness information, such as RAP, includes safety aspects, operational factors, and the uncertainty factors in workmanship and inspection.
‧ Encourage operators to assess and implement safety related airworthiness requirements at the earliest practicable time.
‧ Closely monitor international technology development regarding more effective non-destructive inspection devices and procedure.
The ASC also recommends the Boeing Company to re-assess the relationship of Boeing’s field service representative with the operators such that a more proactive and problem solving consultation effort to the operators can be achieved, especially in the area of maintenance operations, to develop or enhance research effort for more effective non-destructive inspection devices and procedures.
Recommendations sent to FAA/USA include ensuring that the process for determining implementation threshold for mandatory continuing airworthiness information, such as RAP, includes safety aspects, operational factors, and the uncertainty factors in workmanship and inspection. The information of the analysis used to determine the threshold should be fully documented.
Detail safety recommendations could be found in the report. A full report could be downloaded from the ASC website: http:///asc.gov.tw
For additional information, please contact
Safety Investigator: Tracy Jen
Tel: 2547-5200- 167