AOPA Pilot Magazine - January 2018 - 100

P&E

SAVVY MAINTENANCE

WHEN THE ENGINE QUIT on the right magneto during a runup, the author traced the

problem to the magneto itself-but what was the cause?

Is it OK to return the aircraft to service
without an understanding of the malfunction?
In aircraft maintenance, problems frequently
are resolved without a full understanding
of the cause.
generate or document any diagnoses
of aircraft malfunctions. Maintenance
records are never supposed to document discrepancies; they only document
the work performed on the aircraft.
Mechanics are required by regulation to
document what they did, not what they
found to be wrong.
In this case, the A&P borescoped the
cylinders (and found nothing amiss),
cleaned the spark plugs (which he found
to be dirty), and replaced one magneto
(for reasons not disclosed). After verifying that the engine was now working
normally, he appropriately approved the
aircraft for return to service. Subsequent
history of the engine continuing to operate normally thereafter seems to validate
the A&P's judgment.
100 | AOPA PILOT January 2018

LET'S GET PERSONAL

Weeks after I responded to the CFI's email,
something equally frustrating (albeit less
scary) happened to me. I had spent the week
on the Outer Banks of North Carolina, and
was about to depart Dare County Regional
Airport headed for Raleigh-Durham
International Airport, an hour's flying time
away, to visit friends and get a flight review
and instrument proficiency check. The
weather was IMC that morning, so I'd filed
an IFR flight plan. I taxied out to Runway 5
in my trusty Cessna 310 and performed my
usual preflight runup. Much to my shock,
when I turned off the left engine's left mag,
the engine quit cold. Subsequent switch flipping established that the left engine's right
magneto was dead, and the other three mags
seemed to be fine.

Discouraged, I taxied back to the
ramp. It was Sunday-these things always
happen on weekends and holidays-and I
couldn't find anyone to assist me. Using
the "survival tool kit" I always carry in
the airplane's left wing locker, I uncowled
the left engine and inspected all the wiring connected to the right mag, but could
find nothing wrong. I disconnected the
P-lead from the mag-rendering it "hot"-
and then retried my runup, but with the
same results as before: When I turned off
the left mag, the engine quit. This made it
clear that the problem was not with the
aircraft wiring or mag switch, but something inside the right magneto itself.
I removed the dead magneto from the
engine and removed the cover to reveal
the mag's breaker points and cam. The
points looked perfect and they opened
and closed normally as I rotated the
mag's drive shaft. I used the small multimeter from my toolkit to verify that the
condenser and the coil's primary winding
were good. I removed the distributor cap
and inspected the coil and carbon brush;
both looked fine. I ohmed out the coil's
secondary winding, and it was OK.
Thoroughly discouraged at not finding
anything wrong with the magneto, I put
it back together and hung it back on the
engine. Just for laughs, I climbed into the
cockpit and started the engine. I switched
off the left mag, fully expecting the engine
to quit. But it didn't. The engine now ran
just fine on the right mag only.
I recowled the engine, refiled my
IFR flight plan, taxied to Runway 5 once
again, did an ultra-thorough runup, and
launched for Raleigh-Durham. I did an inflight mag check, and everything was fine.
Over the next several weeks, I flew from
North Carolina to Florida to Tennessee to
Texas to California, and the magneto continued to perform flawlessly.
It's frustrating when stuff like this happens. Whenever something goes wrong
with our aircraft, we always want an explanation. But we don't always get one. AOPA
MIKE BUSCH is an A&P/IA.
EMAIL mike.busch@savvyaviator.com

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AOPA Pilot Magazine - January 2018

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