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On June 7, 1998, at 1230 hours mountain standard time, an Arner
Challenger II S, N2NX, an experimental aircraft,
 experienced a
loss of engine power during cruise and collapsed the landing gear
after making an emergency landing in a dry wash near Pleasant
Valley, Arizona. The aircraft, operated under the provisions of 14 CFR Part 91, sustained substantial damage. The private pilot/owner
and one passenger were not injured. Visual meteorological
conditions existed for the personal flight and no flight plan was
filed. The flight originated from the Pleasant Valley airport at
1215.
The pilot reported that they had departed the Pleasant Valley
airport approximately 15 minutes before the loss of power was
experienced. Approximately 6 miles south of the airport, the pilot
noted a loss of rpm's and could not maintain level fight. He
stated that he chose a dry wash area to make the emergency
landing. After touchdown the aircraft sank into the sand and came
to an abrupt stop.
The pilot conducted an engine inspection on-scene.
He observed a
broken spark plug retainer spring and the detachment of the spark
plug wire cap associated with it.
When you inspect
your plug wires look for corrosion and split boots.
Photo courtesy
http://www.tcsn.net/mswihart/mark/safety.htm
The following was emailed to me but I do not know it's
origin - DL
Spark Plug cap tips -
It’s that time of the month again, and here I go
with another little maintenance tip for your Rotax powered bird.
This month’s tip is about an often over looked item of extreme
importance to our power plants well being. The spark plug cap! Now
some of you may be saying why the spark plug cap who ever looks at
those??? That is exactly my point, even on complete rebuilds this
little electrical item is often overlooked and not replaced.
A brief recap of the two types of caps that are
currently being used on our engines is in order. Originally Rotax
engines were equipped with breaker point ignitions and Bosch
spark plug caps. A breaker type ignition is not the hottest spark
producer at low cranking speeds and at low RPM’s.
Because of this a
spark plug cap with a 1000 ohm resistor built inside was used along
with a sheet metal type shield on the outside of the cap. The
intention of these two items was to reduce EMI, “electro-mechanical
interference” or RFI, “Radio frequency interference”.
This is
necessary to reduce the interference our engine’s electrical system
imparts on our aircraft radios, Gps’s, and for you not so
politically correct low flying guys, even our neighbor’s TV sets.
 Later engines equipped
with stronger dual electronic ignition systems may use a 5000 ohm
NGK resistor cap, these may be either black or magenta in color,
mechanically these are identical.
Along with these resistor caps the newer engines
also are equipped with resistor spark plugs. All of this just to
reduce that annoying hum or whine you may hear in your headset while
your engine is running.
OK, so now we all know more than you wanted to
about this resistor spark plug cap, what ‘s the big deal? Well I
have i nclude a few photos
below of a cutaway of these caps for your viewing pleasure.
Notice the resistor built right inside these caps, take care when
removing them from your engine never pry these caps off with a
screwdriver etc as they are fragile and can break easily.
The other key item that we need to be aware of is
the connector inside of the cap that actually makes contact with the
spark plug top. This connector on the Bosch caps is a simple metal
tap that only makes contact on one side of the plug top. The newer
NGK caps have a machined brass insert that fully surrounds the plug
top and it also has a small metal wire spring to ensure it “snaps” into place on the
spark plug.
The normal high frequency vibration our engines
produce while running will eventually wear out the connectors in
either type of cap and both the electrical and mechanical connection
will be compromised. It is extremely important for the people with
inverted engines to check these regularly.
As for you upright guys
and gals, these should still be checked at least annually and
replaced whenever wear is detected. Also watch for corrosion between
the cap and plug top. These can be coated with dielectric grease, as
all connections on our planes should be.
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