Engine Inflight Shutdown - Carburetor ice, maybe?

[Ramiro Silveira]

Ipu? ? Ca?apava ? S?o Paulo ? Brazil
August 09 2015
15:45 UTC - 12:45 LT
Airplane: RV-6 (430 h)
Engine: Lycoming O-320-H2AD (1900 h SMOH)
Carburetor: Marvel Schebler MA4SPA (20 h SMOH)
Let?s go to the account of what I remember:
Flight from SNJR to SDIP: 146 NM
I did the first half of the flight 6500 ft below the clouds base, needing to descend slightly below 6000 ft near the Chapada das Perdizes, Serra das Broas, in the region of the small cities of Carrancas and Minduri, then up to 8500 ft above the top of the clouds near to the small city of Cruz?lia.
I made a long descent fromf 8500 ft to 3000 ft after crossing the Serra da Mantiqueira passing by the southeastern part of the city of Campos do Jord?o.
It was not at idle, but was greatly reduced in order to prevent the speed increase since close to the hill there was a little turbulence so the ride was bumpy.
The temperature was low and there was moisture in the mountains, by the way the layer was very thick.
It is important to notice that I did not open the carburetor hot air, but it was not forgetfulness, it was by sheer neglect!
I arrived at Ipu? flying high and fast on a far away downwind leg for runway 08, stilldescending and dodging the vultures, then reduced the engine a little bit more in order to circle and slow down.
I saw the windsock was standing upright, a reason to plan a shorter traffic pattern , as usual on such occasions.
Rejoining the downwind leg I accomplished the standard procedure to turn on the auxiliary fuel pump and enrich the mixture. I advanced thrust lever lever a little bit then set it to idle just abeam the numbers.
Reducing to 100 mph, I set flaps down and continued pulling the stick in order to bring the speed to 80 mph, looking for vultures when I realized that the noise was different.
At this time, I operated the throttle without answer, then shortened the path to the runway while confirming the pump was on, the mixture was rich and switched from the left tank to the right fuel tank.
No answer.
It was then that I realized the thrust was to far forward and I what I did was to reduce it slowly.
The engine responded briefly at low power, but soon quit again.
Before that I had already set flaps up in order to reduce drag and improve my glide ratio. I confess that this time I breathed very relieved to see how the plane responded to this action, because I had a ****ing horrible taste in my mouth looking at the fence and the bog just before the runway tubes and thinking that could have to land there.
When I was sure that the landing was assured I forgot about the engine and focused on the landing, I slipped with full right pedal and slowed down in order to set flaps down again.
The touch was soft after a wind puff that made me float more than desired.
Relieved, I took the momentum to get out of the runway and stopped on the side lane.
I remember the smell of fuel.
I turned off everything and left the plane there in the sun for a time estimate about 15 min.
I went back to the plane, drained the tanks and confirmed that it was avgas.
I climbed into the cockpit, performed the normal starting procedure and the engine caught on the first prop turn.
It was a little rough close to 1000 rpm, but operated fine with the mixture slightly poorer, making rotation to rise over 100 rpm.
I checked full power: normal.
I checked magnetos: normal.
I checked mixture: normal.
I checked idle: normal.
Then I taxied back to the hangar, did all the checks again: normal.
Turned it off, put inside the hangar, closed the doors and went to have an ice cold Heineken beer, as cold as the ice I suspect that formed in my carburetor.
I still don?t know if it was a mechanical failure or just an operational error, but only God knows how much I am grateful to have left unharmed.
I look forward to hear advices from the VAF friends experienced in Lycoming?s and similars to search the flea that is behind my ear (donkey ear of course for not opening the carburetor hot air)...

[BillL]

It sounds like carb ice. No evidence and no way to prove. Throttle off, high humidity, = ice. A mixture change might have helped recover some power.

Good flying. Happy I have injected

[riobison]

Yes, it does sound like it.

The Vans Aircraft are very tightly cowled with lots of heat in the cowling so probably less likely to get carb ice but they are still susceptible.

35 years ago I was taught that whenever I reduce power setting to 2200 rpm or less, I always pull on carb heat first and leave it there until I land or my RPM is over 2200 rpm. It has worked well all of these years

Tim

[Mousse]

Hence the value of having a carburator temp. gauge. I seldom have to activate my carb heat in my -9 knowing what the temperature in the carburator is. I would not fly an aircraft without one in my part of the world.

Glad your end result was good.

[N941WR]

I doubt it is carb ice, but it could be. My experience has been that when you slow down, the carb temperature goes up because there is less air moving through the cowl to cool things down.

I my Phase 1 (first 40 hours of testing), I had four engine stoppages that acted like carb ice. In my insulation, mounted on the forward side of the firewall, I have an aluminum "U" fuel line that goes between the gascolator and the fuel flow meter.

The "U" was not insulated and during prolonged flight, at low power settings, enough heat built up to boil the fuel in that line. Once I insulated the "U" with fire sleeve, the problem went away completely.

If you have any un-insulated fuel lines in your engine compartment, I would insulate them and see if the problem returns.

[Ramiro Silveira]

Bill,

You are right, it could be, but even on much hotter days I never had any sign of vapor lock.
My engine is an O-320-H2AD, the mechanical fuel pump is mounted in the front part of the engine, just above cylinder no. 1, right in front of the cowling air inlet, all fuel lines run over the cylinders, the coldest area under the cowl.
All fuel lines are insulated in fire sleeves.
On the other side, we are in the winter here, it was cold outside, and it was the first time I was so dumb not to use carb heat.
Regards,

Ramiro

[N941WR]

Ramiro,

Are you using 100LL or Auto Fuel? If you are using Auto Fuel, does it have any ethanol in it?

[Steve Melton]

on some humid days my O-320 with MA4SPA temp ~ 10-18C will get a periodic burp at cruise power below ~7K altitude as it ingests carb ice. pulling carb ice 1/8 open eliminates it. on cold days, less than 10C I do not develop carb ice. probably each engine/carb configuration will respond differently. I would not fly on a carb'd engine without having a good working carb heat option.

[Ramiro Silveira]

Bill,

Auto gas in Brazil has more than 25 % of ethanol.
I never use it.
I always use only AVGAS 100/130 with lead (the only type available here).
EMBRAER, the company that I work for, manufactures a cropduster powered by a Lycoming IO-540 with pure ethanol, the same bought by drivers on any gas station in the city, and it works fine, producing more power than gasoline.

Steve,

I have carb heat and it works fine, I always use it, but on this day I was stupid and did not use it.

Regards,

Ramiro

[Weasel]

Originally Posted by Ramiro Silveira

with pure ethanol.......... producing more power than gasoline

Ramiro

......huh?