The Bureau of Air Safety Investigation recommends that the
engine manufacturer AlliedSignal determine the sensitivity of
turbine wheel seals to the initiation of fatigue cracks from slot
corners, as a function of slot corner radii.
As a result of investigation into this occurrence, the Bureau
simultaneously issues the following interim recommendations and
safety advisory notice:
IR19990112
The Bureau of Air Safety Investigation recommends that the engine
manufacturer AlliedSignal audit the process employed to manufacture
TPE 331 turbine wheel knife-edged seals to determine those factors
that may lead to excessive variations in slot corner radii.
IR19990114
The Bureau of Air Safety Investigation recommends that the engine
manufacturer AlliedSignal consider, during engine design and the
formulation of continuing airworthiness instructions, the
possibility that turbine wheel seal fatigue failure may result in
hazardous modes of engine failure.
IR19990115
The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority Australia conduct an audit of that part
of the aviation safety system that establishes the operational
history of life-limited components, to establish why the
operational history of second-stage turbine wheel, p/n 868272-1,
s/n P03214C, could not be determined with certainty.
SAN19990116
The Federal Aviation Administration should note the safety
deficiency identified in this document and take appropriate action
as considered necessary.