Reciprocating-engine powered low-capacity transport aircraft (8
to 10 passengers) provide an important public transport connection
throughout regional Australia. In the period January 2000 to
December 2005, twenty powertrain structural failures of high-power
(300 to 375 brake horsepower) horizontally-opposed, reciprocating
engines were associated with air safety occurrences reported to the
ATSB. These occurrences ranged in severity from; in-flight engine
shutdown; engine failure and forced landing; engine failure
combined with in-flight fire and fracture of both upper engine
mounts; to the fatal accident of a regular public transport flight
following the structural failure of both engines to ditching at
night. It is evident that the reliability of high-power
reciprocating engines is an important requirement for the safe
operation of this class of aircraft. This research investigation is
a study of the factors that affect reciprocating engine
reliability.
The study found that powertrain structural failure was not
restricted to one engine model, one engine manufacturer, or one
powertrain component. The events that initiated sequences that led
to engine in-flight failure could be grouped into three categories:
combustion chamber component melting; bearing breakup; and
powertrain component fatigue cracking. Analysis of the factors that
were associated with each category of initiating event revealed
that powertrain component reliability is affected by the
development of shockwaves during combustion, the response of
bearings to boundary lubrication and out-of-plane alternating
loads, the increase in component alternating stress magnitudes, and
creation of stress-concentrating features in components during
engine operation. These factors may act singly, but on many
occasions it is the synergistic effect of the presence of multiple
factors that result in a sequence of events ending with engine
in-flight failure.
The recurrence of powertrain component structural failure events
suggests that the corrective actions that are a part of the
airworthiness assurance system may have been ineffective.
Corrective action is dependent on accurate analysis and feedback.
It is evident that analysis is affected by the complexity of
reciprocating engine systems and feedback requires a broad view of
the interaction of systems and a detailed view of the components of
a system.