After 2 years and 9 months
since its occurrence, the Aviation Safety Council (ASC) today
releases the CI611 occurrence
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 findings related to the
· 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 should collaborate
with their regulatory authorities to take appropriate action on
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
and eventually cause 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
· 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 &
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
· 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 any
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 were 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 and these 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 can be found in
the full report.
As a result of this investigation,
the ASC has issued 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
Among the recommendations sent to CAL
· 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
· 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
· 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
· Encourage operators to assess and
implement safety related airworthiness requirements at the earliest
· Closely monitor international
technology development regarding more effective non-destructive
inspection devices and procedure.
The ASC also recommends that the
Boeing Company should 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
Detailed safety recommendations may be
found in the report. A full report may be downloaded from the ASC
For additional information, please
Safety Investigator: Tracy Jen
Tel: 2547-5200- 167