Had my first - "This isn't working, no flying today"

WDD

WDD

Final Approach
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Oct 16, 2019
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Vintage Snazzy (so my adult children say)
First sunny day in what seems an eternity, and got rental time on the Tiger.

Preflight looks good, taxi up to run up area, and then check the left mag. RMP's drop by 200, plane violently shakes, sounds like hitting only 2 (maybe 1?) cylinders. Leaning to burn off carbon has no effect. Just to check, both mags, full throttle - only goes up to 2100 RPM. Called Ground, and taxied back to ramp. No flying today.

Yikes - it was rented/flown only a few hours before. Glad it broke on the ground and not with the previous renter 3000' up.. First time I've ever had a problem with this club / flight school.

I've sometimes wondered why we do run ups - no one ever really finds anything wrong. I've changed my mind on that.
 
WDD said:
I've sometimes wondered why we do run ups - no one ever really finds anything wrong. I've changed my mind on that.
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I've fund problems on runup more than once. Fouled plugs and a loose plug wire that I can remember off hand. I'd never think of skipping it.
 
Did you try leaning it? If the previous pilot ran rich, it may just be fouled plugs, which can be cured by running lean to burn the crud off. No need to cancel because of that.

regardless, good call. You didn’t feel it, you didn’t go. Better to be down here wishing you were up there. This won’t be the last time, stick to it.
 
Yep. Leaned it as much as it would without killing the engine. Ran it like that for several minutes. No effect.
 
Good call! There’s always another day!
 
I’ve had a problem during takeoff that the run up didn’t even catch, and had to abort. The run up is obviously important, but I learned that day that vigilance during the takeoff roll is equally important.
 
Maybe sucked in an intake gasket. Good call. I’ve investigated accidents where the pilot knew some was wrong but still tried to take off, ending in death.

especially after maintenance, run it up full power, make sure gauges look good and nothing spews from the cowl.
 
WDD said:
First sunny day in what seems an eternity, and got rental time on the Tiger.

Preflight looks good, taxi up to run up area, and then check the left mag. RMP's drop by 200, plane violently shakes, sounds like hitting only 2 (maybe 1?) cylinders. Leaning to burn off carbon has no effect. Just to check, both mags, full throttle - only goes up to 2100 RPM. Called Ground, and taxied back to ramp. No flying today.

Yikes - it was rented/flown only a few hours before. Glad it broke on the ground and not with the previous renter 3000' up.. First time I've ever had a problem with this club / flight school.

I've sometimes wondered why we do run ups - no one ever really finds anything wrong. I've changed my mind on that.
Click to expand...
One dead or shorted spark plug will do that. If it was two cylinders dead, it would barely run. It would quit if three cylinders weren't firing.

Could be one plug lead that fell off (not properly tightened) but more likely it's just one plug shorted by carbon. And it was likely fouled by the time previous renters brought it back.
 
In my 2000 hrs TT in single engine airplanes, I frequently had rough mags in the first 60 hrs when I was renting. Never had them in the next 1900 hrs when we did our own maintenance as a club and later as a single owner. This was starting back in the days of 80 octane fuel and then MoGas til last October when I hung it up.
 
Since it is not your plane to fix the following is just FYI. Run for a while on the bad mag only put a hand on each cylinder and if one is colder then it's probably a bad plug, plug wire, stuck valve or in case of fuel injection a plugged injector on that cylinder. I it's equal temp on all cylinders then in my experience the mag has a bad capacitor.
 
Snowmass said:
Since it is not your plane to fix the following is just FYI. Run for a while on the bad mag only put a hand on each cylinder and if one is colder then it's probably a bad plug, plug wire, stuck valve or in case of fuel injection a plugged injector on that cylinder. I it's equal temp on all cylinders then in my experience the mag has a bad capacitor.
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IR thermometer makes this project easier
 
Just last week I notices that the plane wasn't charging during run up. Wouldn't be a bid deal but the Arrow has electric landing gear. I know, I always have the emergency manual down but I don't like relying on only 1 system.

In any case, good call.
 
It may not have broken on the ground. The other guy just may not have noticed if the plug fouled while he was flying.
 
Stan Cooper said:
A stuck exhaust valve will do that (limited RPM, violent shaking). Good call.
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Yeah, but he noticed it when he switched to one mag. A stuck valve wouldn't care whether the mags were both on or on only R or L.
 
I've had all kinds of issues with rentals, I try to avoid them unless it's absolutely necessary. Probably its also why I haven't flown but a handful of times in the last year.
  • One rental I had a grounding wire issue, turned the key to off, engine still running.
  • Another taxied all the way to run up and just then had the GPS power off. Turns out was an alternator problem and we were on battery power, had enough juice to contact tower and head back.
  • I was ALMOST stranded twice in the same plane for the same problem. The brakes failed in the left wheel..wouldn't have been a problem if I only needed to make right turns, but alas was not so. Felt a lot like Zoolander...Luckily in both cases found someone with some fluid to give the brakes back some life.
  • Found one plane had a prop-strike and no one reported it, they just left it. Found a burred prop.
  • I've had my com radio die on me in flight, flat tire upon landing, and a whole host of other problems.
At this point I don't even want to fly anymore unless I can do it in my own plane. So tired of all the issues and the plastic container that is always full of oil soaked paper towels and 5 empty oil cans with about 1/2 inch of oil yet the engine itself is a quart low..it's like they just pour it in the container. Then there's the inevitable flat spots on tires, seats that smell like a fat man wore nothing but a smile on his last flight in 100+ degree weather and rubbed his ass all over each seat for fun.

Think I might take another year off and just buy a cheap two seater to tool around in..but yeah, good job @WDD for not flying..that would ruin your day.
 
Dan Thomas said:
Yeah, but he noticed it when he switched to one mag. A stuck valve wouldn't care whether the mags were both on or on only R or L.
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He also said that on both mags he could only get static 2100 RPM @ full throttle. Could have been a bad left mag and a stuck valve?
 
Stan Cooper said:
He also said that on both mags he could only get static 2100 RPM @ full throttle. Could have been a bad left mag and a stuck valve?
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Probably just a bad mag or plug. Any loss of spark has its cost, even if it's only one plug.
 
Drip water on each header works as well

What is better is just having club fix the rental
 
I have my own airplane which is hangared and babied as well as I can, and I go down for maintenance now and again. Latest was a flat tire. Hell, last flight turned into a near emergency when the panel mount Johnson bar holder (sounds vaguely obscene, doesn't it?) got sticky and I couldn't lock the gear down. Oh I got it, but it wasn't easy. Airplanes are machines. They break.
 
WDD said:
...taxi up to run up area, and then check the left mag. RMP's drop by 200...
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Refer to:

Mag switch.jpg
​
Now, is this the kind of mag switch the plane has? The "Left" mag that you say had the big drop was the one labeled "L" or the one in the left position, labeled "R"? If the latter, I'd say the previous renter didn't come back to "Both" after the mag check and flew the entire time on the mag labeled "L", fouling the plugs on the other side.

Btw, "RMP" should be RPM, which clues me into thinking you might have misidentified the mag switch too.
 
dtuuri said:
Btw, "RMP" should be RPM, which clues me into thinking you might have misidentified the mag switch too.
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LOL RMP

Yes - that is what the mag switch looks like
 
Had the same thing happen in a 150...on what was supposed to be my first solo cross country during training. Something in the mag went bad/ out of adjustment. They put a rebuilt set of mags on and I flew the next day.
 
Follow up - A&P found a bad mag as well as something wrong with the wiring harness. Still in shop.

And..... that's why you do the run up test!
 
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