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I am going to step onto my soapbox for a few
paragraphs before getting into this next story; so stay
with me.
Sensors and displays in an aircraft keep the pilot
constantly updated as to the condition of vital systems.
Should a sensor indicate that a critical part of the
aircraft is failed or operating outside of the norm, he
must make sound (sometimes) difficult decisions to
maintain safety for all concerned.
The reported information is used by the
pilot-in-command (PIC) to make go or no-go decisions.
The PIC as ordered by regulation, must be aware of all
things pertaining to a particular flight. These
include weather, condition of the aircraft, condition of
himself; to name just a few. He must have a
detailed understanding of each system of the aircraft
about to be flown and how they interact and affect one
another.
A good pilot is very far from the common image held
of the invincible hot-shot without a care in the world.
The old airplane joke punch-line that says: "don't worry
folks the left engine is out, so we will be getting to
our destination a little later than expected", is
laughable but fatally sad at the same time.
Ok, here's is the rest of the story:
The mission was to transport the Pastor and Director
of our Guatemala mission from Quetzaltenango to
Guatemala's La Aurora international airport.
Thirty minutes by air (4-6 hours driving on the driving
conditions). Prior to passenger arrival a through
pre-flight inspection of the aircraft was completed.
Due to the poor condition of our taxi way, the
aircraft must be towed into position before the engine
can be started. The whole process is a little like
a circus with all parties wearing orange safety vests.
The radios are alive with chatter as permissions and
authorizations are requested and received.
Simultaneously, airport agents are sent (the young and
fit ones anyway) to clear the runway of people and
animals.
With passenger in place, I begin the engine start
checklist. The engine came to life smoothly as
expected. Going down the checklist I observe the
oil pressure gage- in the green (that's good) then the
vacuum gage- good also, one check after another; all
good so far.
Remember those sensors I was talking about at the top
of this article? Critical warnings and failures
are reported in a cluster directly in view of the pilots
line of vision and there it was, a red indicator labeled
"OIL PRESS". Right away I had to evaluate and
correctly interpret the information presented. The
oil pressure gage was telling me everything was OK,
while that red indicator screamed it was not!
The oil pressure sensor when working correctly and
supplied with oil at 20psi will keep the warning
indicator light off and supply power to the Hobbs meter.
On the other hand a separate sensor produces a signal
that is displayed by the oil pressure gage which was
indicating normal at the variety of static conditions I
set.
Understanding how each system worked, I could
visualize that the oil pressure sensor was faulty.
One could argue that there were
secondary systems functioning; I am not one to
gamble with life. Here is
where those sound and difficult decision are made.
In the end, it did cost my passenger a lengthy and
uncomfortable drive; but it did not cost a life.
Afterward, with the engine cowl removed I discovered
what I had envisioned, a ruptured pressure sensor.
The unit presented evidence that it was leaking from the
crimped copper clamp, and had seepage in the connector
end.
As you can see in the photo on the right, oil is
leaking from the body of the oil pressure sensor.
A small mount of oil can be seen pooling and running
down the backside of the engine.
The new part took only a week while moving between
the vendor, US office, then by hand to Guatemala City,
and finally Quetzaltenango. When installing any
component, the preparation includes checking all
publications. There may be a procedural or
technical considerations that must be observed; many
times saving time and effort.
A logbook entry, ground run, and
test flight and we are back in business.........but
that's another story.
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