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cnehus

Safety, hand proping

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Just wanted to share, and hopefully renew a total respect for hand proping. I’ve been starting these aircraft for 30 plus years now and I almost had my second encounter with a moving prop. While pulling a prop thru several times priming a PT22 in preparation of starting , the engine fired and ran for a second then stoped. I was doing everything by the book, pilot in cockpit, calling for “switch off”, “ brake set” , and pilot repeating each command. After my first encounter with a moving prop 25 years ago I learned a valuable lesson......never trust this sucker! Then as now the switch was in the OFF position. Last time troubleshooting found a broken “P” lead, that little wire attached to the back of your magneto. If that wire is not grounded (open) the magneto is HOT. This time around the “P” leads were fine. Troubleshoot found the magneto switch contacts not providing a clean ground while in the OFF position, thus acting like a broken “P” lead, open ground to the magneto.....HOT!

   These switches are getting old, dirty, and worn internally. Special attention should be paid to this simple system every time you start and shut down. If you don’t feel a detent while moving your mag switch thru each position, it’s worn out. At each and every shut down you must accomplish a quick , easy switch check. At idle power select OFF and note engine ignition shut down, then back to BOTH and shut down with mixture as normal. This was drilled into me both during Flight Training and during my A&P training. These switches were not that great 80 years ago when new, Manufacturing was cheep as was the design. 

   I personally have added a second grounding switch to my oil shutoff valve. When the valve is off it adds a second ground to the Left Mag. This is helpful, two fold. Starting with your oil off will be difficult due to this is the impulse (Starting) magneto. Secondly I feel more comfortable moving prop during maintenance with the additional ground supplied to the magneto. I have also added to Annual Inspection a quick check of the condition of the ground supplied to the mags via the switch. It just takes a couple of extra minutes while checking the timing of the mags utilizing  a cheep ohm meter. Make sure the ground is solid to that P lead. If the resistance is high, other than a couple of ohms,  jumping or open , your switch needs attention.

Chris Nehus

N53271

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