Pratt & Whitney Canada PW118A, Engine s/n 115120
INTRODUCTION
Airnorth Regional experienced operational problems with a Pratt
and Whitney Canada PW118A engine (engine s/n PC-E 115120). The
problems ranged from hung starts resulting in aborted hot starts to
vibration (sub-idle vibration) and noise from the high pressure
(HP) rotor. These problems occurred over a period of several days.
In order to resolve the problems the engine was removed from the
aircraft to allow further investigation through disassembly.
Disassembly revealed that the bolted joint between the HP
turbine disk and turbine stub shaft had failed. Of the five bolts
used in the assembly, two had fractured in the threaded section.
The remaining three bolts exhibited varying degrees of bending and
thread damage.
After a detailed examination of the bolts by Pratt and Whitney
Canada, it was concluded that the fracture of the two bolts and
cracking in the remaining bolts was caused by corrosion fatigue,
with sulphur being identified as the corrosive agent. It was
proposed that the presence of sulphur was the result of
environmental contamination.
Airnorth brought the bolt failure and subsequent analysis by the
engine manufacturer to the attention of the ATSB. An independent
review of the bolt failure analysis was undertaken by the ATSB.