Can your Breather Tube breathe?

Discussion in 'Hangar Talk' started by TangoWhiskey, Oct 20, 2006.

  1. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    Time to start thinking about winter flying, and some pre-flight checks we might not otherwise do.

    The breather tube (which vents engine crankcase moisture generated as a by-product of the combustion process) can ice up in cold weather, causing back pressure that can blow out oil seals—a bad thing. You lose your oil and the engine seizes.

    An excerpt from an edition of the Lycoming Flyer, entitled "The Whistle Slot", states:

    "Moisture is expelled from the engine crankcase through the breather tube which often extends through the bottom of the engine cowling into the air stream. Under very cold conditions, this moisture may freeze and continue a buildup of ice until the tube is completely blocked. It is normal practice for the airframe manufacturer to provide some means of preventing freeze-up of the crankcase breather tube. The breather tube may be insulated, it may be designed so the end is located in a hot area, it may be equipped with an electric heater, or it may incorporate a hole, notch or slot which is often called a "whistle slot."

    The operator of any aircraft should know which method is used for preventing freezing of the breather tube, and should insure that the configuration is maintained as specified by the airframe manufacturer. Because of its simplicity, the "whistle slot" is often used. Although the end of the tube may extend into the air stream, a notch or hole in the tube is located in a warm area near the engine where freezing is extremely unlikely. When a breather tube with whistle slot is changed, the new tube must be of the same design."

    Therefore, cold weather operations emphasize checking that the breather tube is not iced up or blocked.

    Do you know which method your aircraft's manufacturer used to prevent freezing of the breather tube? Do you know where it's located, and how to check it?

    If not, you might want to ask your mechanic to show you…

    Here's what can happen if you don't:

    http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20001207X03054&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001207X02834&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001206X01346&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001211X15697&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X18647&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20041201X01900&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001213X33396&key=1

    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001213X24868&key=1
     
  2. tonycondon

    tonycondon Gastons CRO (Chief Dinner Reservation Officer)

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    excellent point troy. i didnt read through the reports but know of at least a couple engine failures due to this. one was a 172 another was a malibu (i think) the malibu had to do with the airplane being recently purchased from someone in florida. apparently it doesnt get cold in florida so the mechanis down there had not installed the "whistle slot". the guy blew out the main seal around the prop but the oil went all over the belly instead of the windscreen. engine ran and ran, spitting oil out. when he pitched down to start descent, the oil level was down to the absolute minimum for level flight, about 2 quarts, and all of it that was in the reservoir sloshed to the front, uncovering the pick up for the oil pump. engine seized. he put it down in a field, took out a fence, and was violated for inadequate preflight.

    so i always look for that stalagmite sitting under the breather tube in the winter, means that stuff is leaking out!
     
  3. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    Good job, Tony. The glider has a breather tube? I thought they called it a relief tube! ;-)

    Actually, I brought this up because I don't know many CFI's that mention this in the preflight training, it's not in most AFM's, and I bet a ramp survey would find 99% of pilots would say "Huh? What!?" if asked about their breather tube.
     
  4. kthompson2k

    kthompson2k Pre-takeoff checklist

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    I would like to be the first to say Huh..What?

    Good to know though!

    KT
     
  5. mattaxelrod

    mattaxelrod Pre-takeoff checklist

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    Actually, I seem to remember there's a question dealing with this very subject on the commercial knowledge test.
     
  6. Diana

    Diana Final Approach

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    We just had our breather tube extended and it runs out the tail of the Citabria now. There is a large whistle hole near the engine so that it doesn't ice up.
     
  7. CJones

    CJones En-Route

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    If I remember correctly, I think we attached the crankcase vent near trailing edge of the exhaust -- hopefully head from exhaust will prevent freeze-up in flight. Good point to check it preflight, though.

    -Chris
     
  8. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    I think you are right... makes you wonder why it's not in the private pilot pool of questions, eh?
     
  9. Tom-D

    Tom-D Taxi to Parking

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    First, Did you notice the AD mentioned applies to Lycoming engines only/

    and all the refferences are of aircraft that have Lycoming engines?

    Except one

    NTSB Identification: NYC86FGM01 .
    The docket is stored on NTSB microfiche number 31344.
    14 CFR Part 91: General Aviation
    Accident occurred Saturday, April 19, 1986 in DORRSEYVILLE, PA
    Aircraft: VERE EZE LONG EZE, registration: N40FP
    Injuries: 1 Uninjured.
    THE HOMEBUILT ACFT COLLIDED WITH A DITCH DURING A FORCED LNDG SHORT OF THE RWY AFTER A POWER LOSS DURING A TEST FLT. THE PLT HAD NOTED SMOKE IN THE COCKPIT AND A LOSS OF OIL PRESSURE. AS HE RETURNED TO THE ARPT THE ENG BEGAN TO RUN ROUGH AND SURGE BEFORE QUITTING. DURING THE LNDG THE LNDG GEAR SEPARATED FROM THE ACFT. DURING ENG EXAM THE CRANKCASE BREATHER TUBE WAS KINKED AND THE OIL SUMP WAS EMPTY OF OIL. THE ENG TURNED FREELY WITH COMPRESSION ON ALL CYLINDERS. NO SIGN OF MECHANICAL FAILURE WAS NOTED. THE LOWER SECTION OF THE ENG WAS COVERED WITH OIL FROM OIL BEING PUMPED OVERBOARD THRU A SEPARATED CRANKCASE OIL SEAL.


    The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

    LUBRICATING SYSTEM,OIL SEAL..SEPARATION
    FLUID,OIL..LOSS,TOTAL

    Which I think was a total mistake to add this one to your refferences (it doesn't say the tube froze up.)


    WHY?
    Because the EZ series aircraft have the engine mounted in backwards. in other words the prop shaft sticks out the back, and all airflow is toward the rear, causing the oil to go overboard. not down the crankcase..and the EZ series do not have the breather tube in open air, it is routed below the cylinders and stops just forward of the engine cowling rear opening.

    I think sombody blew that one. so to speak.
     
    Last edited: Oct 20, 2006
  10. Tom-D

    Tom-D Taxi to Parking

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    When you stop to think the airflow from the crankcase to the breather is caused by blow by of the rings doesn't it make sence that the air excaping the tube is hot? And thus the moisture only condenses after leaving the tube.

    Thats why you see steam coming out of the tube most days.
     
  11. CJones

    CJones En-Route

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    That is true.

    At least with the end of the tube being near the exhaust, if it IS frozen shut before engine start, hopefully the exhaust heat will help melt said ice and allow the gases to escape before it has time to build up enough pressure to blow a seal.

    -Chris
     
  12. Steve

    Steve En-Route

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    http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001208X07773&key=1

    What that report doesn't include is the fact the oil came from a failed main seal. The plane actually made 3 approaches to land. During the first "3 bouncer" the broken tailwheel allowed the breather tube, routed to the tail, to be crushed, closing off the opening. On the second go-around the tower asked the pilot to "turn off his smoke system" as it reducing the visibility on the runway for the other planes landing. To which the pilot replied "I don't have a smoke system. On the third attempt the plane touched down left of the runway pavement, ballooned as it crossed an abandoned taxiway, and collapsed its main gear when it touched down again. It slid about 300' on the wet grass before coming to rest on its belly. The pilot was shaken but not injured. He sat there for a moment, opened the canopy, and stepped out on the ground as a light rain fell.

    How do I know the details? I was standing about 200' from where it came to rest.

    I guess he didn't have a whistle slot.

     
    Last edited: Oct 20, 2006
  13. gismo

    gismo Touchdown! Greaser!

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    I had mine firesleeved. The theory is that this provides enough insulation that the heat of the oil vapors keeps ice from forming.
     
  14. Steve

    Steve En-Route

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    I wonder if air/oil separators are plaqued with this issue. :dunno:
     
  15. bbchien

    bbchien Touchdown! Greaser!

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    This was the one that really did it for me....
     

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  16. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Mine does. Didn't start with him until partway thru instrument training, but I swear I learn something new every time I fly with him that's completely unrelated to the actual purpose of the flight. :yes:

    When he taught me about the breather tube, I went

    because

    and then, not two weeks after he taught me about breather tubes, one of the other club members had the breather freeze up on one of the Archers and blow an oil seal. He managed to put it on the ground before the engine seized, but he did lose four quarts in the process. :hairraise:

    I bet you're right.

    Why the heck isn't this in the AFM's? :dunno:
     
  17. mikea

    mikea Touchdown! Greaser!

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    Ditto. I have one.

    I need to look to see if I have the whistle port ahead of it.
     
  18. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    Nope, I didn't notice that! Thanks for pointing that out, Tom. That's what I love about these forums... ALWAYS LEARNING!

    Sure 'nuff! Good observation.

    You're right! I shouldn't have had that one in my list. You get the silver mouse award for actually opening and reading them! :yes: :cheerswine:

    Makes perfect sense.

    I sure did! Thanks for edu-muh-catin' me!
     
  19. Tom-D

    Tom-D Taxi to Parking

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    Did you notice the temp at the time of the accident? (-29) I'll wager the aircraft did not have the winterization kit installed.

    When you operate in temps below -20 things change alot, and you must be prepared for it.
     
  20. tonycondon

    tonycondon Gastons CRO (Chief Dinner Reservation Officer)

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    brrrrrrrrrrrrrrrrrr
     
  21. Cap'n Jack

    Cap'n Jack Final Approach

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    Looking in a POH for a C-172, it wasn't obvious to me about what to look for (I rent). Any hints? Also, thanks for the lesson.
     
  22. tonycondon

    tonycondon Gastons CRO (Chief Dinner Reservation Officer)

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    down by wear the gascolator drains out there is another tube, about 1/4 ID tubing or so. That is the crankcase breather tube. if you follow it up through the cowling it will lead to the crankcase. if the airplane has been sitting since the last flight and it is below freezing out, there should be a little pile of ice under the tube, this indicates that the tube is not frozen shut and has been draining. if there is no pile and the plane has not moved since the last flight, have a look up there and see if you can see any blockage. looking up towards where it goes into the crankcase you should be able to see the whistle slot. typically it will be a "X" cut into the hose. up at that point, the tube will have turned into a rubber hose.

    And remember, if Tom or any of the other A&Ps on the board tell you that i am wrong, believe them. But im pretty sure ive got it right.
     
  23. Cap'n Jack

    Cap'n Jack Final Approach

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    Tony-

    I think I know what you mean. It is a stainless steel tube, about 3/8 inches across? I've wondered what that was!

    Thanks!
     
  24. tonycondon

    tonycondon Gastons CRO (Chief Dinner Reservation Officer)

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    thats probably it, if its sticking out the bottom of the plane, ask your local A&P he will definitely be able to tell you and will probably appreciate your interest.
     
  25. gismo

    gismo Touchdown! Greaser!

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    That could be a drain from the "back" side of your fuel pump or a manifold drain as well.
     
  26. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    Resurrecting an old topic. Just read this incident report from a pilot in Richland, WA who ran into this issue. PDF with pictures and the pilot's story. I'm betting he had no whistle slot installed in the tube.
     

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  27. Bob Bement

    Bob Bement Pattern Altitude

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    Some aircraft with a Oil type Vacuum pump will also have another vent tube in the same location as the crankcase vent. At least it is on my 182 with an 0-470 cont. I have a whistle tube on mine by the way.
     
  28. Dan Thomas

    Dan Thomas En-Route

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    A 1/4" or 3/8' tube on a 172 is the battery box drain. The crankcase breather is a 3/4" aluminum tube, big enough to stick a forefinger into. If you look up higher you might see some black foam insulation on it, as per the Cessna parts manual.

    A 1/4" tube on some may be a manifold drain, as another poster noted. It drains excess fuel from the bottom of the intake manifold if overpriming occurs. On the Lycoming, that manifold is part of the oil sump and so it looks like it might be venting the crankcase, but it's not.

    Dan
     
  29. gismo

    gismo Touchdown! Greaser!

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    The author of that story has some gross misunderstandings about his lubrication system. Specifically, there's no way that a plugged breather would produce a pegged oil pressure reading. Normal pressure in the crankcase is around one or two inches of water (about four to eight hundredths of one PSI). If the breather gets plugged completely this might build to one or two PSI before the crankcase seal fails and relieves the crankcase pressure. He also incorrectly states that the oil pressure relief valve will limit the pressure in the system to it's normal setpoint. This is simply not true because that valve when wide open can only pass a limited amount of oil and if the oil is cold and thick the oil pump can easily pump more than the open relief valve can return to the crankcase. At normal oil temps this isn't a problem unless the spring in the relief valve is weak and someone has tightened the adjustment down and/or added washers under the spring which can severely limit the amount the valve can open.

    And FWIW, I installed firesleeve tubing over my crankcase vent lines which insulates them from the cold air passing over the top of the engine. This is supposed to keep the crankcase gasses hot enough that the rest of the breather (aluminum tubes that run down the back side of the engine and out the bottom of the nacelle) from getting below freezing. The metal portion of the vent also runs near and between the exhaust pipes which also help keep things too warm to freeze. AFaIK there is no slot or small hole in the breathers on my engines and I've flown in some mighty cold temps (-35F) without any evidence of frozen breathers.