Pitot System Blocked

[DPM20J]

I noticed my pitot tube was blocked a couple weeks ago, seemed like a very fine material (a mud dauber?).  I tried to remove it the best I could.  On Monday, upon take-off, my gear warning sounded and the by-pass button light was flashing.  My ASI was showing 60 knots and was not moving higher.  I kept a slow climb, afraid to raise the nose as may ASI airspeed was not increasing.  I pressed the by-pass switch and cycled the gear.  Eventually, my ASI showed an increase.

My pitot system has to be blocked somewhere.  I spoke to our FBO mechanic.  They are swamped and not able to get to it.  He said, (tongue in cheek) if it was in their shop, they would blow out the pitot line in reverse to try and remove the blockage.  I tried to find an access to the pitot line.  Obviously, it ends up at the ASI, but there has to be an easier access point where I am able to get compressed air to the plastic pitot line.  I tried unscrewing the pitot tube itself, but it does not drop down far enough to get at the tube connection where I could at least blow out the pitot itself.

I am thinking the pitot drain would be a good location to get at the pitot line.  Where would I access the pitot drain, from the belly?  Does anybody have experience with this issue?

In hindsight, after I found the pitot blockage, I should have rigged up a vacuum or something to suck out any material from inside the pitot tube.  Lesson learned.

Any help will be appreciated.

[Pinecone]

Do NOT put pressure or vacuum on the pitot tube or line until you disconnect it from ALL INSTRUMENTS.

You WILL damage the instruments.

[DPM20J]

Thanks, I do realize that.  I need to isolate and disconnect the line going to the pitot tube and blow compressed air back toward the pitot tube to reverse the blockage.  I believe the best location to do this would be at the pitot drain beneath the left wing root, or at the ASI itself.  Getting at the rear of the ASI itself is definitely a process.

[dzeleski]

1 hour ago, DPM20J said:

I noticed my pitot tube was blocked a couple weeks ago, seemed like a very fine material (a mud dauber?).  I tried to remove it the best I could.  On Monday, upon take-off, my gear warning sounded and the by-pass button light was flashing.  My ASI was showing 60 knots and was not moving higher.  I kept a slow climb, afraid to raise the nose as may ASI airspeed was not increasing.  I pressed the by-pass switch and cycled the gear.  Eventually, my ASI showed an increase.

My pitot system has to be blocked somewhere.  I spoke to our FBO mechanic.  They are swamped and not able to get to it.  He said, (tongue in cheek) if it was in their shop, they would blow out the pitot line in reverse to try and remove the blockage.  I tried to find an access to the pitot line.  Obviously, it ends up at the ASI, but there has to be an easier access point where I am able to get compressed air to the plastic pitot line.  I tried unscrewing the pitot tube itself, but it does not drop down far enough to get at the tube connection where I could at least blow out the pitot itself.

I am thinking the pitot drain would be a good location to get at the pitot line.  Where would I access the pitot drain, from the belly?  Does anybody have experience with this issue?

In hindsight, after I found the pitot blockage, I should have rigged up a vacuum or something to suck out any material from inside the pitot tube.  Lesson learned.

Any help will be appreciated.

The blockage is most likely in the pitot tube itself so I would remove it and the line and clean it that way. In short, remove the cover, remove the line, and blow compressed air in reverse.
 

That being said if I recall the regs correctly from memory the pitot system will need to be re certified since it will be opened up. So you probably want someone to re certify the system after you take it apart to be legal and safe.

[FlyingDude]

11 minutes ago, dzeleski said:

The blockage is most likely in the pitot tube itself so I would remove it and the line and clean it that way. In short, remove the cover, remove the line, and blow compressed air in reverse.
 

That being said if I recall the regs correctly from memory the pitot system will need to be re certified since it will be opened up. So you probably want someone to re certify the system after you take it apart to be legal and safe.

No you don't recertify as in 91.411 ifr xpdr test. You haven't touched the devices so why recertify them?

Your AP needs to do a leak test on the line that was opened and then log that the system is leak-free.

[dzeleski]

11 minutes ago, FlyingDude said:

No you don't recertify as in ifr xpdr test. You haven't touched the devices so why recertify them?

Your AP needs to do a leak test on the line that was opened and then log that the system is leak-free.

Sorry my terminology probably was incorrect. I dont mean everything needs to be retested just the pitot system itself is working correctly. Either way I dont believe thats something a pilot can sign off on.

[DPM20J]

I tried removing the four screws that attach the pitot to the wing.  The pitot will slide down, but not far enough to disconnect it from the pitot air line at the top.  I hate to pull too hard as to create further issues.

[PT20J]

21 minutes ago, DPM20J said:

I tried removing the four screws that attach the pitot to the wing.  The pitot will slide down, but not far enough to disconnect it from the pitot air line at the top.  I hate to pull too hard as to create further issues.

You have to open an access panel under the wing just inboard of the pitot tube to undo the connections to the pitot tube in order to remove it. The panel may be attached with pop rivets which must be drilled out. When done, replace the pop rivets with countersunk aluminum pop rivets.

Skip

[DPM20J]

Thanks... I will let you the outcome.

[carusoam]

The airspeed indicator / pitot static system is connected to a few things…

See if you have a static drain that isn’t closing properly… under tail cone near the N on the tail number…

See if you have a pitot drain that isn’t closing properly…  under pilot side wing near root

Gear safety switch is also attached to the line…

Water in the static system usually is a small scale error…

 

People test the pitot system with a rolled hose fit to the front of the pitot tube…

Its a very sensitive instrument that is easy to break… no compressed air or vacuum needed…

 

Bugs don’t typically go very far into a tube…

Is the access panel not allowing access to the pitot connections?

See if you can expose everything so that a mechanic can more readily do the mechanic specific part….(?)

PP thoughts only,

-a- 

 

 

[1980Mooney]

On 8/5/2022 at 11:08 AM, DPM20J said:

 I need to isolate and disconnect the line going to the pitot tube and blow compressed air back …I believe the best location to do this would be at the pitot drain beneath the left wing root, or at the ASI itself.  Getting at the rear of the ASI itself is definitely a process.

 There are 2 drains on the "Pitot Static" system.  One is on the Pitot line (under pressure when flying) and is located beneath the left wing root.  The other is on the Static line and located on the bottom of the tail cone. The Pitot drain cannot be accessed from under the plane or in the wing root.  It is accessible from the interior by removing the kick panel trim or entire panel by the Pilot's feet.  It is hard to get to and you run the risk of creating new leaks if you disconnect the tubing.  You should only disconnect the pitot or static lines to the drains if you think they and/or the drain are leaking.

Accessing the pitot line behind the ASI will allow you to blow everything back.  You should break the connection at the instrument panel and at the Pitot Tube connection.  Take your glare shield off and look either from above or on your back from below  You should be able to access the connection between the pitot pressure tubing and  the connector on the Pitot tube by removing one of the wing access panels.  You can then clean out the Pitot tube separately in isolation.  Look for bug remains, egg deposits, mud, etc.   I replaced my heated Pitot tube quite a few years ago this way . 

Also see 2 articles in KNR Shop Talk - both are February 2016. - about midway in the document.  You can search "pitot" and find them.

 ShopTalk (knr-inc.com)

 

Edited August 7, 2022 by 1980Mooney

[PT20J]

If you do blow it out from the airspeed indicator end of the line, be sure nothing else is connected to the pitot line especially the airspeed safety switch.

[1980Mooney]

@DPM20J  I assume that you have looked at both the Parts and Services manuals for the J. Both are accessible free online and here on MS. 

 

Edited August 7, 2022 by 1980Mooney

[N201MKTurbo]

I have always found the blockage to be in the pitot tube itself. I have had to soak it in water for a while to soften the mud, then let water run through it for a while to wash out as much mud as possible. A pipe cleaner or some weed wicker string would be ok to get it clean too. On the road, I have used small tree branches to clean it out. All this with the pitot tube removed from the plane.

You never realize how much you take the ASI for granted until it doesn’t work. It is a bit unnerving.

[DPM20J]

I figured I’d start at the pitot tube first.  Drilled out access panel rivets.  The tube connection to ASI was fairly easy to access.  Disconnected this line.  I only had a 2 gal air compressor.  I set the pressure to 50 psi and tried several times to reverse blow the pitot.  Although air was exiting the pitot tip, it didn’t seem like it was nearly as much as was being put in.  I let the tank fully charge and fully opened the tank valve to 125 psi.  This time something shot out the tip with a BB gun sound.  From the foul smell on my hand, it must have been a large insect.  The air was now free flowing through the pitot.  I didn’t have countersunk rivets.  I’ll get some from our FBO in the morning to reattach the panel.

My pitot will now always be covered when parked.  As noted above, you take for granted an error free ASI, especially when the reading is far from normal at takeoff, with your gear alarm sounding.

Thank you all for your help and thoughtful comments!!

[Marauder]

I figured I’d start at the pitot tube first.  Drilled out access panel rivets.  The tube connection to ASI was fairly easy to access.  Disconnected this line.  I only had a 2 gal air compressor.  I set the pressure to 50 psi and tried several times to reverse blow the pitot.  Although air was exiting the pitot tip, it didn’t seem like it was nearly as much as was being put in.  I let the tank fully charge and fully opened the tank valve to 125 psi.  This time something shot out the tip with a BB gun sound.  From the foul smell on my hand, it must have been a large insect.  The air was now free flowing through the pitot.  I didn’t have countersunk rivets.  I’ll get some from our FBO in the morning to reattach the panel.
My pitot will now always be covered when parked.  As noted above, you take for granted an error free ASI, especially when the reading is far from normal at takeoff, with your gear alarm sounding.
Thank you all for your help and thoughtful comments!!

Don’t feel bad. I had one of these attached to my pitot tube.


It worked great until one day it decided not to flip up.


Sent from my iPhone using Tapatalk Pro

[Will.iam]

6 hours ago, DPM20J said:

I figured I’d start at the pitot tube first.  Drilled out access panel rivets.  The tube connection to ASI was fairly easy to access.  Disconnected this line.  I only had a 2 gal air compressor.  I set the pressure to 50 psi and tried several times to reverse blow the pitot.  Although air was exiting the pitot tip, it didn’t seem like it was nearly as much as was being put in.  I let the tank fully charge and fully opened the tank valve to 125 psi.  This time something shot out the tip with a BB gun sound.  From the foul smell on my hand, it must have been a large insect.  The air was now free flowing through the pitot.  I didn’t have countersunk rivets.  I’ll get some from our FBO in the morning to reattach the panel.

My pitot will now always be covered when parked.  As noted above, you take for granted an error free ASI, especially when the reading is far from normal at takeoff, with your gear alarm sounding.

Thank you all for your help and thoughtful comments!!

Since you are making a commitment to cover the pitot tube, now would be a good time to also plug your wing tank vents with a shop towel so that you don’t get the oil can experience or worse fuel starvation to the engine because a bug decided to make that it’s home because you covered it’s original home with a cover. By using a shop towel I have 90% of the towel hanging down so it reminds me to remove it just like the remove before flight streamer the pitot cover has on it. Since the left wing vent tube is so close to the pitot tube it is very hard to miss when I go to remove the pitot I get the vents as well, plus I have it added to my preflight checklist as well. 

[ArtVandelay]

Since you are making a commitment to cover the pitot tube, now would be a good time to also plug your wing tank vents with a shop towel so that you don’t get the oil can experience or worse fuel starvation to the engine because a bug decided to make that it’s home because you covered it’s original home with a cover. By using a shop towel I have 90% of the towel hanging down so it reminds me to remove it just like the remove before flight streamer the pitot cover has on it. Since the left wing vent tube is so close to the pitot tube it is very hard to miss when I go to remove the pitot I get the vents as well, plus I have it added to my preflight checklist as well. 

I made up covers using some plastic tubing:

[Fly Boomer]

1 hour ago, ArtVandelay said:

I made up covers using some plastic tubing:

I'm borrowing that idea!  I have been looking for a plug of some kind, but this looks even better.

[Will.iam]

11 hours ago, ArtVandelay said:

I made up covers using some plastic tubing:

Very interesting that your vent is pointing down. Mine are pointing at a 45 degree into the wind. I just assumed all mooneys were like that. I wonder why they switch to an angle? Will take a pic next time I’m over at the hanger. 

[kortopates]

3 hours ago, Will.iam said:

Very interesting that your vent is pointing down. Mine are pointing at a 45 degree into the wind. I just assumed all mooneys were like that. I wonder why they switch to an angle? Will take a pic next time I’m over at the hanger. 

Yours is protected from icing by being in a NACA duct, which is why the vent has to bent to keep in the profile of the NACA duct; otherwise the duct can't protect it. 

[PT20J]

16 hours ago, ArtVandelay said:

I made up covers using some plastic tubing:

Not a bad idea. Curious about the placard, though. That one is supposed to be adjacent to the sump drain. Did someone replace it and put it in the wrong place?

[carusoam]

Great follow up DPM!
 

Air vent…

Not so much fuel drain…

It will take an unusual attitude to get fuel to show up there…. Then fuel will drain out…

 

Mud daubers do like parking in the vent hole… even inside hangars…

Naca ducts are a bit harder to see their location under the wing… don’t forget them…

 

PP thoughts only…

-a-

[Pinecone]

I guess for the vents in the NACA ducts, you would need a plug to fit in the tubing opening.

[ArtVandelay]

Not a bad idea. Curious about the placard, though. That one is supposed to be adjacent to the sump drain. Did someone replace it and put it in the wrong place?

I guess so, I had it repainted a few years ago, never noticed the placard.