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Output Number
R20000025
Approval Date
Published Date Time
Recommendation type
Recommendation
Mode
Aviation
Date released

The Australian Transport Safety Bureau (formerly the Bureau of
Air Safety Investigation) recommends that the engine manufacturer
General Electric identify the source of the casting defect of the
failed HPT blade.





As a result of investigation into this occurrence, the Bureau
simultaneously issues the following recommendation and safety
advisory notice:





R20000026



The Australian Transport Safety Bureau (formerly the Bureau of Air
Safety Investigation) recommends that the engine manufacturer
General Electric review the adequacy of turbine blade manufacturing
process controls to reduce the likelihood of blades containing
casting defects being released into service.





SAN20000027



The Federal Aviation Administration should note the safety
deficiency identified in this document and take appropriate
action.

Organisation Response
Date Received
Organisation
General Electric Usa
Response Text

The loss of rib cross section area from fatigue that initiated
at a casting anomaly, combined with internal surface Intergranular
Oxidation (IGO), reduced the shank cross section area and resulted
in a tensile separation of the Ansett CF6-80A Stage 2 HPTB S/N:
MSCBH987. The loss of load bearing area due to fatigue that
initiated at a casting anomaly is considered to be the primary
cause of the separation.



The fatigue damage originated at a casting anomaly (dross) located
in the center of the 3-4 cavity rib. The dross was introduced
during the original casting process in 1983. Due to the location
and size of the casting anomaly, detection by nondestructive
inspection techniques (FPI and X-Ray) is not considered
likely.



The IGO seen resulted from long time engine exposure (31,593 hours,
23,072 cycles) and is not unusual on high time blades that do not
have an internal coating. The current part configuration, released
in 1992, includes an internal aluminide coating to preclude
oxidation.



A retirement recommendation is currently in place to address
internal oxidation (IGO) seen in high time Stage 2 CF6-80A HPT
Blades without an internal aluminide coating (KTW, TRM and PCM
Serial Numbers). Though IGO is not considered to be the primary
cause of the separation, a retirement threshold recommendation will
be evaluated for high time Stage 2 CF6-80A HPT Blades without an
internal aluminide coating (MSC Serial Numbers).