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.
As a result of the investigation into this occurrence, the Bureau
simultaneously issues the following interim recommendations and
safety advisory notice:
IR19990113
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.
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.