Crankcase Breather Tube

[Colonel Sanders]

It's winter again ...

If you fly a piston engine aircraft, you should be aware that there
is a tube running from the crankcase to the outside of the airplane,
generally (but not always) running out the bottom of the cowling.

This tube is very important. The piston rings don't seal perfectly,
and there is a certain amount of "blow-by" gases from the combustion
that makes it past the rings.

So, the crankcase is basically pressurized, and the older and more
worn the rings, the more pressure there will be in the crankcase.

To vent the pressure in the crankcase, where the oil is kept in a
wet sump engine, most aircraft manufacturers run a simple tube
from the top of the crankcase to the bottom of the engine. And
that simple arrangement works pretty well in the summer - unless
you put too much oil in the crankcase, and it barfs the extra oil
out onto the belly as the crankcase whips up the oil in the sump.

However, water is a byproduct of combustion, and in the winter,
an emulsification of oil and water is present at the end of the
breather tube, and it can freeze and plug the tube shut.

When this occurs, very bad things happen. The crankcase continues
to be pressurized by blow-by, and the next weakest link is the
crankshaft seal at the front of the engine, where the prop is bolted
on.

The seal blows, and the engine oil gets blown out, covering your
windscreen. You will notice when this happens.

To avoid this, you need to drill a hole or two - some people call
it a whistle valve - farther up the breather tube, inside the engine.

Some people like to wrap the holes with one wrap of electrical
tape and hope it blows before the crank seal, but that makes
me nervous. I don't cover the upper vent holes, and if a little
engine oil makes it into the engine compartment, oh well. That's
why God invented Mineral Spirits and textile rags.

Last year a friend of mine landed his Robinson helicopter for
gas on a very cold day (for us) here in Eastern Ontario. I
noticed what looked like brown snot hanging down from the
breather tube. I broke it off, and realized that it was plugged
solid.

I got my jacknife out, and dug out 4 inches of solid ice that
had formed, plugging the end of the breather tube. Fortunately
the manufacturer had drilled 2 tiny holes further up the tube,
and they were venting the crankcase gases.

Recently, we took up the 3 Pitts. It was below freezing, but
not terribly cold. 2 vents had no ice, and the third was almost
totally plugged up! I have no idea why that one tube plugged
up as the airplanes are almost completely identical.

Anyways. You're Canadian. You fly when it's cold. You should
know about this potential problem, and please check to make
sure that you have a small hole (or two) drilled up in your
crankcase tube, if you're going to fly in the winter!

Guess what happened to these guys, flying across the
North Atlantic? I don't think they planned this landing
in Greenland:



I doubt Tex in the photo was familiar with this problem,
but you are now!

[Big Pistons Forever]

The solution is simple just fly on the West Coast, it is + 8 deg C here today

For those unfortunates not blessed with the ability to live in Paradise, heed CS's advice; it is timely and very appropriate.

[KnownIce]

Just prior to logging into AvCanada I watched the following video on Youtube about this very topic, affecting a Glasair II that did not have vent holes drilled higher along the tubing.

The pilot reported elevated oil pressures as one hint of this problem. It's a rather drawn out narrative that doesn't really add much to what CS wrote but thought some might be interested.

[bverwegen]

A few years back at Sault College one student landed on Vermillion Lake outside of Sudbury because of an oil pressure indication which resulted from the crankcase breather tube being clogged. Since then the AME's have put the holes at the top as suggested and no problems since. We also take another measure at the school where if it is below -15 celsius we drain the sludge valve directly. Safe flying all.

[azimuthaviation]

Last year a friend of mine landed his Robinson helicopter forgas on a very cold day (for us) here in Eastern Ontario. Inoticed what looked like brown snot hanging down from thebreather tube. I broke it off, and realized that it was pluggedsolid.I got my jacknife out, and dug out 4 inches of solid ice thathad formed, plugging the end of the breather tube. Fortunatelythe manufacturer had drilled 2 tiny holes further up the tube,and they were venting the crankcase gases.

Those tiny holes werent put there by the manufacturer but probably a forward thinking AME at some point. Ive seen that happen in an R44 before, the vent tube is straight down, so landing in soft snow plugged the warm tube then solidified as ice. In that case there was a rupture in the engine, loss of oil and forced landing. I enquired about a psv in the crankcase vent inside the cowl or somewhere else in the engine but no ones stc'ed such a thing yet.

[Colonel Sanders]

Keep drilling those holes! If anyone asks, you don't know
anything about them - they were there, first time you saw
the aircraft.

[PanEuropean]

I am perplexed why the engine and airframe manufacturers have not solved this problem by other means - perhaps by routing that tube near something that is hot, or installing a larger diameter tube, or making an alternate design available for cold weather operations.

Michael

[Spinner]

I was just searching but could not find a reference to the breather line holes in any bulletins etc. I was sure there was a service letter or bulletin for either the Cessna or Piper aircraft regarding installing a hole in the breather line. I had a straight navajo puke oil out of one engine because someone had covered the emergency breather hole with a tyrap while securing the line to the engine. The end of the breather which was level with the cowling, had frozen over in the cold.

[Colonel Sanders]

manufacturers have not solved this problem by other means

I really doubt they are even aware of the problem. And given that the solution
to the problem is so simple - drill a hole or two, a distance up from the exit - I
don't know why you would need to engineer a more complicated solution.

You may or may not have been alive on 28 January, 1986 when the Space
Shuttle Challenger exploded shortly after launch. You probably don't remember
the blue-ribbon panel that was appointed to find the mysterious cause of the
accident. This blue-ribbon panel consisted of Neil Armstrong, . Yeager,
and many other distinguished people such the genius Richard Feynman, who
worked on developing the atomic bomb during WWII, later won the Nobel
prize in physics, played a mean set of bongo drums, and was also widely
known for seducing his co-workers' wives.

Anyways, this panel of certified geniuses, after many months, eventually
discovered that o-rings shrink in the cold and then stuff leaks, which if you
live in Florida might not be obvious, but if you're a Canadian and you've
lived through a winter or two, you've probably noticed that stuff - including
o-rings - shrinks in the cold. Heck, even George on Seinfeld eventually
figured that out!

Don't take cold wx ops for granted. A good example: what is the "pour point"
of your aircraft engine oil? Why would you care? What indications would you
observe that you have encountering problems with it?

[bverwegen]

Heck, even George on Seinfeld eventually
figured that out!

+1

[PanEuropean]

I really doubt they are even aware of the problem.

I am absolutely certain that the manufacturers involved (engine and airframe manufactures) are 100% aware of the problem.

I work for an aircraft manufacturer, in Flight Safety, and I can assure you that whenever there is any kind of incident reported involving an aircraft that we manufacture, the incident (and causal factors) are very closely looked at, if for no reason other than to determine if a change in procedures, maintenance practices, or product design is required.

Hence I am wondering - if moisture freezing in the crankcase breather tube and blocking the breather tube is a known issue - and it certainly appears to be a known issue - is it possible that some kind of Service Letter, Service Bulletin, or alternative maintenance procedure has already been promulgated by the engine or airframe manufacturer that provides mitigation for this problem? The 'home-made' solution of drilling a hole or holes further up in the breather tube, to allow gases to escape if the distal end of the tube becomes blocked, sounds like it might work, but I would expect the OEMs to device and publish a solution themselves.

I guess what I am getting at is this: Before going out and implementing an unapproved repair scheme (drilling holes in the crankcase breather tube), it might be appropriate to have an AME who is familiar with both the engine and the airframe do a careful literature search of the SLs, SBs, maintenance practices, and continuing airworthiness instructions to see if the OEM has already published an approved solution for this problem.

Michael

[azimuthaviation]

Why arent the cranckase gases vented into the intake like every other engine?

[North Shore]

Anyways, this panel of certified geniuses, after many months, eventually
discovered that o-rings shrink in the cold and then stuff leaks, which if you
live in Florida might not be obvious,

Actually, Sanders, the problem was well-known to the Morton-Thiokol and NASA engineers, as it had happened a few times before in previous launches. In those cases, however, the O ring had, for whatever reason, re-seated itself and continued to function as per design. The larger problem at work was the normalisation of deviance, which 'allowed' them to keep launching, even though one critical piece was not performing to spec.

A really great read about this is a book called 'Riding Rockets' by Col. Mike Mullane. He devotes a serious chapter in an otherwise hilarious book to the Challenger accident and its aftermath. http://www.amazon.ca/Riding-Rockets-Out ... 0743276825

[old_man]

Why arent the cranckase gases vented into the intake like every other engine?

Less efficient actually and more importantly it is not required by emissions standards as far as I know. Much like why they don't

-use unleaded gas like every other engine
-have a catalytic converter like every other engine
-use a closed loop fuel injection system like every other engine.
-etc

Car engines and airplane engines are are in different eras when it comes to technological innovations. The reasons for this are an entire different subject.

[cgzro]

. http://www.lycoming.com/support/tips ... eneral.pdf

This lycoming document describes the problem.

For non aerobatic planes this hole or slot is open year round but inverted systems you have to open them manually in the winter.

[Colonel Sanders]

The "hot setup" is actually to vent the crankcase breather tube
into the exhaust. This improves performance by a few horsepower
but this maddeningly simple thing is distinctly non-trivial, as the
red bull racers found out!

With this setup, you can see the puff of blue smoke out the exhaust
when someone's Christen 801 air-oil separator tank overflows.

[Blakey]

Most aircraft are designed and built in warm or temperate locations. This problem usually manifests itself in cold locations. The manufacturers probably don't see it as a major problem and the provision of an alternate vent in a warm location is a safe and effective fix of long standing so they don't need to address it.

I've seen the same situation with crews from warm climates not understanding the import of operating their aircraft, and the cold-weather systems installed on them, in cold climates. Sometimes the attitude seems to be, as they used to say at Air Florida, "We'll cross that bridge when we come to it".

[Colonel Sanders]

crews from warm climates

Ask them what the pour point temp of their piston
engine oil is, and what two implications of it are, for
cold temp ops.

[Blakey]

I doubt that any of them would have any idea what you are talking about as they have no experience with fluids thickening in cold weather. In truth, in other than large complex aircraft, the pour point is irrelevant. Once the oil is cooled below it's cloud point temperature, it is not safe to operate the engine without thorough pre-heating as the precipitated crystals will clog your filters and or screens. I recall one frosty February morning in Gander when a crewmember of the C130 parked next to us came over to find out how we intended to start our aircraft. They were from a Gulf State and they had been trying to start their cold-soaked aircraft for an hour or so but couldn't get it to light off. Our Engineer had to assure them multiple times that it was OK to use the Nacelle pre-heat system to warm the engine, melt the wax crystals and thaw all the frozen O-rings and seals so that the fuel would flow. They had no idea what Nacelle pre-heat did and were afraid to use it. Truth be told though, these crews are usually very good at hot-weather procedures so it all evens out.

[Colonel Sanders]

In truth, in other than large complex aircraft, the pour point is irrelevant. Once the oil is cooled below it's cloud point temperature, it is not safe to operate the engine without thorough pre-heating

Lots of small piston aircraft have had serious problems with engine
oil pour point. I personally know of a C310 that was crashed because
of it - double engine failure.

If you look at the spec sheet for a straight-grade engine oil (eg Aeroshell
W100) you will find that it has a pour point of -20C. Below that temperature,
in the (constant speed) prop hub or oil cooler, it can congeal. It is no longer
a nice liquid. When it congeals in the prop hub you may find it difficult to
change the prop RPM which is annoying.

But when it congeals in the oil cooler, it plugs it up and the oil pressure
soars far above the redline. There was even a recent episode of Ice
Pilots about this, but as usual for TV it was not explained coherently.

This is why you want to run a multi-viscosity oil in the winter, and
it's not just about the preheat. The pour point of Aeroshell 15w50
is -40C which is far below that of the straight grade W100 (sae 50).

Even with Aeroshell 15w50, do you want to operate below -40C?
Not me.

Executive summary: even with pre-heat, don't run summer straight
grade oil in the winter.