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Oil breather blocked, caused sudden engine failure


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Hi Canardiens,

 

 

A couple of weeks ago, I had a very interesting ( but scary...) incident with my COZY... It could have been the end of my COZY..., and easily the end of me!

 

First, sorry for the rather long post, but I'll first give a brief summary: I own (I'm not the builder) a European COZY powered by the good old Lycoming O-235-C2A. Last February, I changed all 4 cylinders with brand new ones, due to low compression and as well to comply with Service Instruction 1504, which warns about cylinder cracks in O-235 cylinders... After all they had done their part, +2500hrs of hard work.

 

The engine was nicely broken in, flown for a hard hour (75%) with initial seating of the rings observed, by a drop in CHT's. All was normal... Then, |I had to leave the aircraft grounded for almost 8 weeks, due to work commitments in a foreign country, +3000 miles away.

 

So end of April, I had the chance to do the further engine break-in. The annual conditional inspection was done just before the next flight, no major work was needed.

 

During the 2 month grounding, my wood (epoxy covered) prop, was overhauled (sanded, dents repaired, repainted and balanced) by a professional prop overhaul shop and looked shining new. All looked very promising...

 

Weather was nice, wind blowing down the 6600ft runway at about 12kts. Conducted a thorough pre-flight, oil, airframe, controls, etc... and then fueled it up with 15USGAL each side. Runup was normal, temps in the green, ready for action!

 

Initial take off acceleration was normal, although I thought the engine was a little on the rough side. I blamed the little rough running, on the new cylinders, the fact that the engine hadn't been running for 8 weeks and/or due to the overhaul of the prop. After all, it could have been just an idea in the head as well...?

 

Climbed out at about 85kts, was about to retract the gear (the good old manual way), when I changed my mind and left it a bit longer... after all it was, kind of a "test flight", and there was still a little bit of the 6600ft (1900m) runway left in front of me!

 

Just after the thought of leaving the gear down a bit longer flashed through my mind.... " deathly silence"! I had experienced a sudden, total engine failure, from maximum take-off power, to "no power at all". Felt as engine failure due to some kind of fuel starvation, like pulling the mixture to idle cut-off or selecting the fuel selector to the off position. I had about 200ft above the sea level airport, when the engine failed. A split second decision was made to land straight ahead on the remaining runway. All engine controls (throttle, mixture and even the carburetor heater) were quickly pulled aft and the airbrake and both rudders were deployed. Nosing down to the concrete I made a brief flare followed by a "kiss landing". Speed must have been around 100kts. Too fast, but after all, there was no alternative and there was little runway left.

I guess, on touchdown, there must have been, about 1000ft to 1200ft (300-400m) left to the end of the 6600ft runway. Maximum brakes were immediately applied. I was ready to retract the nosewheel in case I couldn’t bring it to a halt on the concrete. Somewhere halfway thru the deceleration, I felt a slight shuddering in the nosewheel, followed by a little dip of the nose position and a somewhat faster deceleration. The Cozy stopped about 10m (10yards) short of the runway end.

 

Disembarked and noticed that the nosewheel fork had broken off, most probably due to nosewheel shimmy. The entire nosewheel was missing and the NG-15 was still intact.

The parts were recovered in the grass about 200ft on the side of the runway.

 

The first thought that flashed thru my head, was some catastrophic engine failure, due to a problem with one of the new cylinders. With the aircraft back in the hangar and both cowlings were removed, I did a thorough check of the engine together with an A&P. The lower spark plugs were all black like coal and oily (except the nr 4 one, which was pretty clean). The prop that was shinny white before the incident now had a large amount of black soot on it. There was now evidence of large oil leaks. A little bit of oil/fuel deposit was found on the lower cowling, but nothing extreme.

 

After a thorough inspection of the fuel and ignition system, the engine was started and was found to be running normal. The carburetor was overhauled, since initially a failure of the Carbu needle was suspected causing a much too rich mixture and resulting in a sudden power loss. Nothing was found in the Carbu, except some small sediments in the Carbu bowl, nothing major.

 

Of course I wanted to find out what had caused the engine failure ...

 

During the 8 weeks (before the flight) that the aircraft was not flown, I had prepared a new oil breather canister, to collect the water and oil deposits. The old one had done its time and needed replacement. Basically it's an empty shaving cream canister, that I painted in an ALU color about 6 weeks before the incident. The old one had large 3/4inch holes drilled in the top sides, this to let it breath to the outside. Unfortunately before installation the day before the flight, the holes were mistakenly not drilled in the new one, so the oil breather system was completely airtight and had no breathing function at all, except a very small hole in the plastic tube that connected with the canister.

 

Most probably the engine failed due to an almost total sealed oil breather system. On NOV 27th 2000, Phillip K. Camarda, posted a very similar incident with his LEZ on Marc’s forum. I have copied the following extract of his NOV 2000 post;

 

<<<<< On Friday Nov 24th I called the mechanic that had overhauled my engine and

told him what had happened. He asked to see the aircraft and root cause the

failure. We removed the upper and lower cowls from the plane and started

trying to find out where all the oil had come from. It came from the crank

seal and a magneto seal. It seems, what had happened was the engine breather

vent line had iced up. The moisture in the engine breather line had froze

due to the cold air and caused excess crank case pressure. The extra

pressure in the crankcase affected the mechanical fuel pump by adding

additional pressure to the top of the diaphragm. The extra pressure, caused

the pump to increase fuel pressure beyond the carbs needle and seats

ability to stop it from entering the float bowl. Once the float bowl became

filled it would run out the float bowl breather port directly into the

venturi throat.

This caused the engine to become flooded with fuel and

drowned out the plugs. The exhaust pipes were filled with black soot and

the plugs were as black as coal.>>>>

 

 

Since I haven't found anything wrong with the engine apart from the oil breather system, I suspect the reason for the engine failure to be the above one. And yes, of course I immediately drilled the holes in the canister!

 

First, I could hardly believe that an engine could suddenly fail due to oil breather blockage, without any serious vibration and oil leakage... but after reading Phillip's post, the story with the excessive fuel pressure, made much more sense! You would rather expect heavy oil leaks and blown seals in a case like that, wouldn't you?

By the way, my O-235 has a nose oil seal retainer installed

 

There is no evidence of damage or leaking seals. So, should I do anything special before the next flight, except a full power run-up ...

 

What are the thoughts of you guys...?

 

 

Finally, “what do I have learned from this incident...? “

 

1/ Finish one job at a time... don't say as I did, " I'll paint the canister first and then drill the holes later". Especially when there is a couple of weeks between making a part and installing it. Have attention to details... small things like this can ruin your day... or even worse, "kill you"!

 

2/ Runway "behind" you, before take-off is useless. Had I not been using the full 6600ft runway length, I would not have been able to stop it on the concrete.

 

3/ When serious problems develop at low altitude (200ft on mine), do not do any trouble-shooting! Once committed to land, close throttle and mixture idle cut-off, in order to avoid a burst of power during the emergency landing...Fly the aircraft first! Had I been doing some kind of trouble-shooting first, before committing myself to land, I most probably would have not been able to live this story... The airport I took off from, is completely surrounded with residential areas. There is hardly any escape possible a low altitude neither straight ahead nor beside the runway.

 

4/ After Take-off, Climb at Best Angle of climb to a safe height, especially when flying out of highly populated areas." Altitude is your best friend"!

 

5/ The fact that the engine was running a little rough on take off, should have been the sign to abort the take-off. Remember, your aircraft talks to you and it’s up to you to listen to it!

 

 

6/ Having +7000hrs in aircraft ranging from 1000lbs (450kgs) to 825.000lbs (375.000kg) does not protect one from similar incidents... Experience helps, but does not exempt you from similar occasions. The fact that I used to instruct at this very airport helped me in the split second decision I made to land straight ahead.

 

 

 

All comments on the above is more than welcome…

 

If interested I can email you guys privately, some pictures of the oil breather canister and of the broken nose gear fork.

 

 

Keep it safe,

 

Regards,

 

Cozylover :confused:

Flying was my first love and it will be my last one!

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Hi Canardiens,

 

Lately I experienced quite a nasty engine failure (at 200ft after T/O), due to a blocked oil breather. If you don't know what I'm talking about, please read the first post of this and then continue...

 

In the meantime I have received a very comprehensive explanation from a Lycoming guy... Here it comes:

 

Biggles

 

 

From: "mahlon_r" <mahlon_russell@t...>

Date: Sun May 16, 2004 10:03 pm

Subject: Re: Oil breather blocked, caused sudden engine failure.

 

 

Biggles,

Not all Lycoming's use the diaphragm style fuel pump, but most 4- cylinder engines and carbureted 540's do and a few IO-540's as well.The O-235 series uses the diaphragm style pump. The other style fuel pump Lycoming uses, is a rotary pump..This pump is mounted with 4 nuts in a rectangular pattern. The diaphragm pump is a lever action,style pump that is mounted with two bolts.

The first thing you need to know is that the diaphragm style fuel pump's relief valve is vented into the crankcase. What happens, is when the breather is restricted or completely plugged up, the air pressure inside of the crankcase increases due to the fact that the natural blow by past the piston rings is no longer vented to atmosphere. The more you run the engine, the more the

pressure builds with a plugged breather. The fuel pressure keeps increasing as the crankcase pressure increases, due to the fact that the pump is sensing a higher reference pressure through its vent into the crankcase. Eventually the crankcase pressure rises to a point, that the fuel pressure becomes excessive and this high fuel pressure literally forces the needle valve in the carburetor open, when it really wants to be closed. Once this happens, the float level in the carburetor rises and the engine gets richer. eventually the float level becomes so high that the float chamber overfills completely, and fuel overflows out the bowl vent, in the carburetor throat, into the engine's inlet airflow. This produces an extreme, overly rich

mixture that won't burn properly and the engine stops running. Basically, it's flooded. Had you pulled back on the mixture control you might have been able to find a sweet spot and kept it running! Once back on the ground, with the engine shut down the crankcase pressure eventually equalizes back through the rings through an open intake valve to be at atmospheric again. So when you try and restart, it fires right up like nothing was wrong. You have to continue to run the engine to build up the crankcase pressure until the whole thing happens again, to re-experience the problem again. If you don't run the engine long enough you think the problem went away.

It is a really dangerous condition because it takes a while for the crankcase pressure to build up enough to make the engine quit. Unfortunately, that seems to be a few minutes into the flight. It is very important to have a vent in the breather line in case the end of the breather freezes up in the winter. In addition to the standard vent, in the breather pipe or hose, what I would do is put a two-inch long razor blade slit in the hose that connects the breather pipe to the engine or in the breather hose, if no pipe is used, right

near the engine with the slit up. This is a secondary safety device, when things are normal, the razor blade slit stays closed as there is no pressure in the overboard line. If the breather becomes frozen or plugged for some other reason, the air pressure in the overboard hose will increase and force the slit to open up and the pressure will be relieved.

As we have discussed plugging up the breather causes the crankcase pressure to increase, this can also cause seals to blow out, normally the crankshaft nose seal. If this happens the crankcase pressure gets vented and the engine doesn't quit but you get a big oil leak. Since your engine quit and you don't have any oil leaks, I don't think you blew any seals. I would do a few ground runs and if no leaks, then a short test flight and check for leaks again. If none are present, I think you are back in business.

Good Luck,

Mahlon

Flying was my first love and it will be my last one!

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