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Engine Inflight Shutdown - Carburetor ice, maybe?

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)...
 
Well written summary.

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 :cool:
 
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
 
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.
 
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.
 
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
 
Ramiro,

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

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.
 
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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
 
......huh?:confused:
If the engine is optimized for it with higher compression and whacko ignition timing, ethanol can make more power than gasoline. When the class allows, a lot of top autocrossers use the stuff.

But your range will suffer mightily...
 
The action that saved you?.

"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."

I have been reading all of the accidents in the RV data base. It is very sobering to see how many people have lost track of their airspeed and stalled on approach after managing the initial emergency. Great job flying the plane.
 
Sounds like a classic case of carburetor icing to me - low power setting (throttle plate closed down,) high humidity (visible vapor in the area,) relatively low OAT.
 
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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

yes, and I should have said good job getting back in one piece. all the best to you and thanks for the post for this experience.
 
Uh oh, looks like it was not ice...
I uncowled and stared at the engine for a few minutes, everything looked fine.
No sign of blue stain typical of avgas on the carb neither below it.
I opened the andair gascolator and checked the filter, it was fine.
After closing the gascolator, I turned the facet auxiliary fuel pump on in order to check for leakage.
Few seconds later there was a big leakage coming from the filter air box.
I had this problem by the end of 2013, when I decided to overhaul the carb, a nice chance to comply with the bulletin regarding the replacement of the metal floats by the synthetic material floats.
I discovered this issue because of a fuel leakage that developed 10 to 15 minutes after a flight.
Few flights later it was leaking again.
The carb went back to the shop that checked it out and I never had fuel leakage again for more than 1 year.
In the morning, I started the engine, very strange behaviour, black smoke and vibration, I tried to shut it down closing the mixture but it did not work, I had to shut it down via ignition switch.
In the afternoon, I started the engine again, a little bit of the same strange behaviour but in less than one minute it was running as usual. I checked full power, mags, idle, everything ok. Shut down normally closing mixture. No leakage during the cool down.
It looks like an intermitent problem.
Fuel system is very simple, on more comment about it is that I have a primer solenoid with a fuel line that goes from the gascolator to all 4 cylinders intake.
Any clues?
 
I'd would second the carb ice. At speed, the total air temp in th carb would be higher. At reduced throttle the temp would drop.

Less than 10c and visible moisture... Suspect ice.
 
Flooding

Is it possible your flooding the engine with the facet fuel pump? Have you checked the max fuel pressure allowed on your carb? Your pump could be over pressurizing the carb, you might need a pressure regulator inline on facet.
 
Hi,

The fault is itermittent, what is causing me difficulties to make it happen again.
Any way, I can only reproduce the fuel leak or the engine rough operation when I command the primer solenoid to open.
So, I am convinced that it is the source of trouble.
Wow, I could never imagine that someday I would fall from the sky due to a so stupid failure.
Now I am thinking about what to do next, replace the solenoid or remove the primer system?
Regards,

Ramiro
 
Supposing that the primer system was the culprit I replaced the parker solenoid valve, the switch and the circuit breaker.
Everything worked fine for the last ground tests and flight hours.
But, unfortunately the problem showed up again last weekend (april 26 2016) in 2 consecutive flights.
This time the engine did not quit completely.
It entered a kind of sub idle mode close to 450-500 rpm when the normal would be 800 rpm.
Reverting back to the carburetor...
 
Carb Heat

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

Absolutely correct on small Continentals, but not on Lycoming per Lycoming 1148C.
 
There are a lot of incidents and accidents that are unexplained with no evidence after the fact. In most cases the assumption has been Carb ice. Hard to prove of course as the evidence has already melted.

One time in 1980 during my flight instruction in a C 172 with a 150 HP Lycoming located in dry Central Alberta in the summer on a clear day. During the run up while checking the carb heat we had fairly severe engine roughness for a minute or so before it cleared up (ice melting). Both my instructor and I were shocked at this. This was not a wet plug, vapor lock or anything like that. This was something different and we agreed that it had to have been carb ice. Obviously the conditions were ideal at that time. So it can happen to any of us with any engine.

Tim
 
My -9 had the same engine with sleeved hoses run over the top of the cylinders as well. The only time I ever had an inflight shutdown was over Lake Michigan after buying mogas at the Manitowoc airport (most likely vapor lock).

It sounds like you've narrowed the issue down to your carb. If you're not confident in your carb, even after rebuild, I'd suggest exchanging it as a core for a new/rebuilt unit from a reputable seller.
 
Sounds like a float sticking to me or not closing due to contamination.....it takes very little. Will cause all the issues you are seeing. Get the carb off and to the shop.
Dave62
 
Andy,

Your photo album about the engine is the greatest source of info about the bad reputation O-320-H2AD that I have ever seen, I love it, I have been watching it many times.
What were the results of your engine quit, did you post it here before?

Dave,

99 % of the people I talk to blame the float or the needle and seat and I fully agree, but how could this remain a problem after the carb have visited the shop 2 times, the first having all parts replaced according to Marvel Schebler standard repair kit including a brand new blue float?

Thanks,

Ramiro
 
Your photo album about the engine is the greatest source of info about the bad reputation O-320-H2AD that I have ever seen, I love it, I have been watching it many times.
What were the results of your engine quit, did you post it here before?

Thanks Ramiro. I was going to write up something of a guide for the H2AD, which is why I took so many pictures. But ultimately I decided against it because I didn't want to encourage others to choose that engine. It worked very well for me, but I don't think the extra 100+ hours of work was worth the savings.

I don't think I posted anything about my experience, and I am almost sure it was vapor lock. Watching the fuel pressure I could see it slowly drop down to almost 0, the engine would die, and the electric pump would bring it back to life again. Fortunately I always kept my right tank full of avgas, which would usually just be used for takeoff, landing, or cross country flight. The fact that I was crossing Lake Michigan is what made it memorable!
 
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