Yesterday I flew to Eugene with a friend I promised I would take flying sometime. Little did he know this would be more of an adventure than he signed up for. The flight there was fantastic. We flew IFR, because it had been a little while since I had been “in the system” and even the the weather was pretty good VFR weather, I like to keep current on at least IFR operations, even if it’s not necessarily in IMC.
Well, we arrived in Eugene, stretched at FlightCraft for a bit, watched the Seahawks kill the Rams, then went out to begin our trek home. Before takeoff, I do what’s called a runup. This is where you do your last minute checks to make sure all the radios and avionics are set, and you also runup the engine to about 3/4 power(1700 rpm in my case) and check the magnetoes. The Cessna 172 engine has a dual magneto system for reliability and efficiency. Each magneto supplies the spark for a spark plug on each of the cylinders. So each cylinder has two spark plugs. Well during the runup procedure you check the left magneto and the right magneto, to make sure that each side is working properly. Because of the redundancy, you would probably never know if one went bad unless you manually shut one side off. Well in switching to the right side, the engine lost between 200 – 250 RPMs and began shaking vibrantly. The POH (Pilots Operating Handbook) for this aircraft states, “RPM drop should not exceed 125 RPM on either magneto or show greater than 50 RPM differential between magnetos”. This can sometimes be “normal” when you have a carbon fouled spark plug. To clear the carbon fouled plug you would increase power and lean the mixture. This, in effect, would burn off the carbon or oil that has contaminated the plug. Well I did that a few times, and the right side magneto never got better. The left side however was running like a champ. I was very bummed, but I opted to taxi back and call the owner to see if he had any other ideas. After talking to him and some other pilots in the area, we all agreed that there was something wrong with the airplane, most likely a bad magneto. So we had to find ourselves a ride home. I was waiting for the Lear 31 pilots that I was talking to, to offer a ride on their way back to Spokane, but that didn’t happen. lol.
My friends wife came down and picked us up and took us back to SLE. We left Salem for a quick flight to Eugene and back at 3pm. I got back to SLE at 9pm. What a day.
Right now the plane is getting looked at and I will keep you all posted on the cause of the problem.