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RECIPROCATING ENGINES
Introduction
Compared to turbine engines, recips are quite difficult
to investigate. First, they always show evidence of rotation
as that is their normal wear pattern. Second,
there is nothing on the recip that consistently captures
evidence of what was happening at impact. That is why
so much attention is paid to the propeller. It provides at
least an indication of what was going on. We will discuss
propellers in the next section.
Basic Steps
Step one in a reciprocating engine investigation is to
assemble everything that is known so far about the accident.
This includes witness statements, radio transmissions
and the basic circumstances of the accidents. Second,
determine what you really need to know about the
engine:
• Was it completely stopped?
• Was it turning at something less than full power?
• Was it turning at something close to full power?
Complete Engine Failure or Inflight Shutdown
If the propeller was feathered, the engine was not rotating
at impact and the feathering occurred at some point
prior to impact. The pilot either deliberately shutdown
the engine and feathered the propeller due to some
cockpit indication or the engine failed and the propeller
feathered itself because an auto-feather circuit was installed
and armed. If the engine merely failed (not deliberately
shut down), then we are not likely to find
much evidence of the cause in the cockpit. In these
situations, a large percentage of engine failures are related
to fuel; or lack of it. We should start with a routine
check of the fuel system:
• Was there fuel on board?
• Was the fuel the correct type?
• Was the fuel free of contaminants?
• Could the fuel get to the engine?
• Did the fuel actually get to the engine?
• Was the engine getting air?
• Was the engine getting ignition?
Internal Engine Failure
If the inspection above fails to reveal a problem, the
next possibility is massive internal damage to the engine
that just made it quit running. If possible, you
might try turning the engine over by hand. The recip is
a rugged piece of machinery and it frequently survives
an impact and can still be rotated. If it turns without
Aircraft Accident Investigation 19
any weird noises, there is probably no internal damage
serious enough to keep it from running.
Engine Did Not Fail, But Was Not Producing Full
Power
There might be several reasons for power loss.
• Induction system ice.
• Induction system failure.
• Spark plug failure.
• Cylinder failure.
• Lubrication system failure.
• Timing failure.
• Turbocharger failure.
Now What?
Still a mystery? OK, stand back and take an overall
look at the engine. Do you see any signs of obvious
mechanical damage? Do you see any signs of a fire that
seem to emanate from a point? A cracked fuel pump
housing, for example, might not be detectable in the
field, but the fire pattern resulting from it might be obvious
if you back up a little bit.
PROPELLERS
Introduction
Propellers are common to both reciprocating engines
and turbine engines (turboprops). An examination of
the damage to the propeller can sometimes be very useful
in determining what the engine was doing at the
time of impact.
Evidence of rotation
You should be able to examine a propeller and determine
whether it was rotating or not at impact. Some
evidence of rotation:
• Blades bent opposite the direction of rotation.
• Chordwise scratches on the front side of the blades.
• Similar curling or bending at the tips of all blades.
• Dings and dents to the leading edge of the blades.
• Torsional damage to the prop shaft or attachment
fittings.
TURBINE ENGINES
Field Investigation Limitations
If the engine needs to be disassembled as part of the
investigation, it is almost always best to take the engine
to an engine facility where there are hoists, mounting
stands, tools and good lighting. Taking a turbine engine
apart in the field just isn’t practical. There are, however,
some basic techniques that can be used by the
field investigator. While these won’t always provide
the final answer, they may give the investigator a pretty
good idea of whether the engine contributed significantly
to the accident. Field examination of a turbine
engine follows a fairly standard protocol.
• Identify and account for all the major components
of the engine.
　
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