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P-LEAD TO MAGNETO INCIDENT
I took a trip last August in Norse
Nomad, my Long-EZ, which has over 400 hours to date.
I had an uneventful flight to McKinney, TX from my home in Carbondale, IL to visit with my son's family. On the way home via Texarkana and Little Rock, I suddenly experienced a noticeable drop in rpm. Since I had put in 20 gallons of IOOLL before departing, I suspected water in the fuel. did a 1801, turn and made it to an airport with the engine running rough and surging between 2400 and 2600 rpm's.
I removed the gascolator and found a half teaspoon of sand and sediment but no water. A quick test flight revealed that I had not found the problem. I decided to leave the Long-EZ, fly home commercially and return with a trailer. To make a long story short, when I got my Norse Nomad home, I started the engine and got a bad mag check on the right mag. The mags had checked perfectly on the previous two flights, but not now.
The culprit was a break in the shielded P-lead from the mag to the starter switch. where the wire made a 901, turn close to the switch. A single strand had cut the insulation and grounded the center electrode!
Knowing what I know now, I would have simply removed the P-lead from the mag and flown home. This would have left me with a "hot" mag but it would have been much better than the 650 mile trailer trip! Also, I did not check the mags in the air when I had the problem. That check probably would have revealed the problem. A sudden loss of about 10% of your rpm is, in most instances, a magneto problem. Another clue was that the cylinder head temperature on my number 4 cylinder was unusually low. This plug runs off my right mag.
Hopefully, this experience may help other EZ flyers who may run into similar problems. Remember, any sudden drop in rpm, check the mags, if possible, check individual cylinder head temperatures, land and disconnect the P-leads. Watch out no one touchs the prop with the mags hot. This may get you home where you can affect proper repairs. Keep in mind that P-leads can shut you down if grounded! These wires should be shielded and installed very carefully to minimize any chance of accidental grounding.
Greetings to all at RAF,