First, I’d check ALL the plugs. For condition and for plug lead connection.. Plug appearance may give a clue. Which mag fires which plug? While you don’t have a maintenance organisation at Kirkwall, there might be some local knowledge. A pilot can remove, clean, replace plugs.
I’d not continue flying with a suspicious mag. EFTO for you could be a ditching. Over the Pentland Firth to Inverness is quite a trip with a dicey mag.
PS There’s a device called a plug lead tester – you might be able to borrow one.
PPS What are your mags time left to testing?
PPPS If I had misfiring, I’d try each mag in turn, and continue on the mag which gave smoothest running. Otherwise on both.
If I had misfiring, I’d try each mag in turn, and continue on the mag which gave smoothest running. Otherwise on both.
That’s probably not a bad plan and FWIW the only mag failure I’ve experienced was an impulse spring failure which dramatically changed the timing on that mag. You would in that case very much want to be running on the other mag only.
Yeah I’ll get some help and take a look at the plugs. That’s definitely happening. At Kirkwall an EFATO wouldn’t be the end of the world, but your right, if I go to the isles for example it wouldn’t be great. I got some bad carb icing just before crossing the pentland firth once… Wasn’t fun!
To answer your questions, I believe the left mag fires the bottom left and top right plugs, and the right mag the remaining 4. I’m not sure how many hours till testing. Thanks for your help.
mentally prepared to close the throttle completely if switching to a particular mag cuts out the engine or makes it rough, before switching back to either a known good mag or to BOTH. Then, after you have switched back to a known good status, re-open the throttle. If you fail to do this you could blow up the exhaust system, because a rotating (i.e. pumping air) engine with no ignition is going to fill the exhaust with unburnt fuel vapour.
Peter, didn’t you mean to write to close the mixture to idle cut-off and throttle half open, then slowly enrich, to avoid back fire? At least that’s what the inflight engine restart procedure says for TB20, and should apply here too, I would think.
I do inflight mag checks regularly, but do pick a location where I am in gliding distance of an airport.
I guess you could use the mixture too, but if you do the mag check at some reasonable altitude, you will probably be leaned just right for peak EGT, so it is better to not mess with the mixture. Using the throttle is simpler.
If you go to full rich at say FL150, I reckon the engine might just stop. Never tried this though…
