One problem masquerades as another

[Katamarino]

Flying along the Albanian coastline, up towards Dubrovnik, at 4,500 feet nicely leaned off, my engine started to hiccup and run a bit rough, as well as being down on power. The coastline was not in sight, behind cloud just off my wingtip. With the cloud around, and 10 degree outside temperature, I immediately thought "carb icing", and pulled on the carb heat. Sure enough, the problem lessened greatly, so I left the carb heat on and steered a bit further from the visible moisture.

A few minutes later, with carb heat still on, the roughness returned, and power dropped even further. I checked nearest airports, and the closest was 48m away; in Italy, over open water. "Sod that", I thought, let's get the coast back in view and stick close to some nice beaches. The cumulus revealed the shoreline so I turned in towards it and called to the controller that I was descending to 3,500; maybe warmer air would help. Because I was descending, I automatically pushed the mixture in...

...and suddenly, all was well! Somehow the mixture had become over-lean. I'm not sure how, as my height was constant and the mixture and power remained untouched, at least until I throttled higher to counteract the suspected carb icing. When I put carb heat on, the less dense air entering the engine brought the fuel-air mix back into line and things smoothened out, reinforcing the apparently incorrect assumption of carb icing. It was only my decision to descend for warmer air, and the instinctive accompanying richening of the mixture, that revealed the true problem.

In future, if the engine hiccups, "mixture rich" will be high on my list!

[greggj]

noted, thanks !

[KNT754G]

Do you have any instrumentation to assist the leaning or is it done "by ear"?

[Keef]

Back in the distant past, I was taught that for engine hiccups, after carb heat, it's "fuel - mixture - mags". I guess that would cover your scenario.

[Gertie]

In future, if the engine hiccups, "mixture rich" will be high on my list!

That's what sorted my one partial engine failure. (I think the cause was that the instructor's knee had fouled the knob and pulled it out when we hit a turbulence bump whilst he was twisted round talking to my family in the back.)

[Katamarino]

Leaning on this aircraft is done "by ear"; therefore I always tend to err a bit on the side of caution. It does have an EGT gauge, but that, along with the Artificial Horizon, Cylinder Head Temperature Gauge, and Com 2, is kaput...

[masterofnone]

Leaning on this aircraft is done "by ear"; therefore I always tend to err a bit on the side of caution. It does have an EGT gauge, but that, along with the Artificial Horizon, Cylinder Head Temperature Gauge, and Com 2, is kaput...

Hopefully "engine" won't be added to the list soon

[Timothy]

In future, if the engine hiccups, "mixture rich" will be high on my list!

That is not a good idea. I have rich cut an engine by doing that, and I was way out to sea.

Mixture - Appropriate might be a better vital action, or even Mixture - fiddle with up and down for best results.

But had you been higher Mixture - Rich could have stopped the engine dead.

[gfry]

In future, if the engine hiccups, "mixture rich" will be high on my list!

That is not a good idea. I have rich cut an engine by doing that, and I was way out to sea.

Mixture - Appropriate might be a better vital action, or even Mixture - fiddle with up and down for best results.

But had you been higher Mixture - Rich could have stopped the engine dead.

Interesting...what sort of height would you say this becomes a real possibilty?

[Timothy]

In future, if the engine hiccups, "mixture rich" will be high on my list!

That is not a good idea. I have rich cut an engine by doing that, and I was way out to sea.

Mixture - Appropriate might be a better vital action, or even Mixture - fiddle with up and down for best results.

But had you been higher Mixture - Rich could have stopped the engine dead.

Interesting...what sort of height would you say this becomes a real possibilty?

I guess that's going to depend on a host of factors, but I was either 90 or 100, I forget.