Airspeed reading zero, possible reasons/remedies besides clogged pitot

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xander75

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xander75
hi folks,
on takeoff roll this weekend, airspeed doesnt come alive stays stuck at 0 on both the steam and aspen PFD 1000. the alititude and VS on both steam and aspen are reading correctly and moving accordingly.

initial diagnose obviously the pitot ram take in being clogged, but there is always a pitot cover on my PA28R200. thought that maybe a bug during taxi could have made it in.

troubleshooting done:
0) could not see any obvious clogging
1) sucked air from the ram intake to hopefully swallow the bug. nothing.
2) blew air gently into the ram but airspeed did not come alive.
3) sucking air out of the drain, this made the airspeed, altimeter, vertical speed all come alive on both steam and aspen.
4) sucked air out of the static of the back of the pitot (this is a 72 arrow ii) with same result of airspeed,altimeter, vs to react.
5) when blowing air into the ram intake, there is some "bypass". which I can understand to be out the drain as it should. I had the notion that if i were to block the drain and static with my fingers and repeat this test that there is still bypass going on.
6) took some small wire into the drain and ram to possibly clean out if there is something stuck, came out clean also (although the wire didnt "bend" in the ram intake so it may be higher up?).
7) took the maintenance cover underneath the wing off, verifying tubes both felt secure, there is definitely 2 tubes, its one of those pitots with both ram (front), drain (bottom) and static (rear).

peripheral info: this plane spend majority of its life down south. I picked her up from AL in march and flew her to MA. It was still mighty cold in MA (<32) at the time. Now it is getting warmer (70-80). could it be that during the last week and half of not flying and some warmer weather that some tubing connections gave way and started to leak?

I would have thought that leaky tubes though would cause erratic readings, but not stuck at zero which merely seems like a complete blockage of the ram intake, right?
since this affects both steam and aspen, it smells like the pitot, but why now suddenly it always having had a cover ...

do you guys have any ideas what this could be and how to remedy/further diagnose?

cheers!
xander
 
You’re working with a Flintstone-simple system.

  • the pitot tube
  • Tubing to instrument
  • Connectors
  • The instrument itself

Something in this short list has a problem.
 
With it stuck with both instruments, I would think that would rule out the instrument. My guess is a loose tube (maybe vibrated off). I think there is a filter in the system also, but not sure.
 
xander75 said:
blew air gently into the ram but airspeed did not come alive.
Click to expand...

xander75 said:
when blowing air into the ram intake, there is some "bypass". which I can understand to be out the drain as it should. I had the notion that if i were to block the drain and static with my fingers and repeat this test that there is still bypass going on.
Click to expand...
Don’t do that, that’s a good way to damage your instruments! Before you blow any air into the ram inlet, always disconnect the lines, but I see you didn’t do that and might’ve exacerbated the issue. Start at the mast and then remove the pitot and static hoses. It may be as simple as something obstructing the holes. If you need to troubleshoot further you can, but it will likely take intervention by your mechanic.
 
thanks for the inputs ryan somorris and rusty. yeah i am suspecting now the pitot tube or its hosing. I am just baffled that it worked just fine a week ago and this weekend it is just zero. although it is pollen season here and some zoo of bugs etc, in 10+ years of flying i never had this! (gotta be a first time for everything right :)

ok let me work with my mechanic to troubleshoot further and not unnecessary damage things. guess this doesnt fall under "preventive maintenance" anymore, hence that be better play.

is there a simple test to do to eliminate one vs the other (pitot/tubing) that might be worthwhile?

once i get with my mechanic and it is diagnosed i'll let you know in case of interest!
 
RyanB said:
Don’t do that, that’s a good way to damage your instruments! Before you blow any air into the ram inlet, always disconnect the lines, but I see you didn’t do this and might’ve exacerbated the issue. Start at the mast and then remove the pitot and static hoses. It may be as simple as something obstructing the holes. If you need to troubleshoot further you can, but it will likely take intervention by your mechanic.
Click to expand...
Exactly. Those instruments are designed to react to very small pressures, and more than one pilot has ruined expensive stuff by blowing and sucking on the pitot or static ports.

Mechanics might be expensive, but doing your own troubleshooting and repairs without knowing what you're doing is a LOT more expensive.

I have heard auto mechanics say that Youtube is the best thing ever for them. It results in lots of business for the car repair shops, fixing or replacing stuff the owner busted as he tackled the job, guided by Youtube "experts."
 
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haha yeah the millennial social media wisdom right :) I know what you're saying.

ps. I did read in some manuals how the IFR pitot static verification is done with syringe tubes to verify for leaks... hence i was thinking that a small pressure change (obviously not a 90psi compressor hose!) to verify the blockage was acceptable.

anyways, mechanic time it is!
 
xander75 said:
haha yeah the millennial social media wisdom right :) I know what you're saying.

ps. I did read in some manuals how the IFR pitot static verification is done with syringe tubes to verify for leaks... hence i was thinking that a small pressure change (obviously not a 90psi compressor hose!) to verify the blockage was acceptable.

anyways, mechanic time it is!
Click to expand...
The airspeed indicator will read 162 MPH with a pressure of one inch of mercury on the pitot. That's about one-half PSI. The altimeter will go to 1000 feet if the static pressure falls one inch. You can peg the VSI and damage it just by varying the static pressure too fast. This stuff is fragile. A friend had to replace all his pitot-static instruments after some kid (probably a kid) blew into the static port. Ruined the bellows in all the instruments.
 
I center punched a large bug at 50 feet on takeoff. Airspeed went straight to zero. In your case since you had no AS at all I suspect you have a hose clamp failure somewhere. Don’t blow into the system. You can break things. Disconnect a hose at both ends before a blow test!
 
And if blowing the static lines don’t forget to disconnect the blind encoder; not always remembered or obvious.
 
In a Flintstone system you need to disconnect and go piece by piece.

Start at either end with your A&P.

If you want to be helpful, maybe take off the inspection panels directly between your pitot tube and the fuselage.
 
You have bug guts in your pitot from hours of flying. Your mechanic will disconnect and run a wire through to clean out the crud. You will be on your way, unless you damaged something trying to diagnose it.

-Diagnosed from the other end of the internet
 
You aren’t going to do the repair w/o a mechanic, what good does the troubleshooting do?
 
455 Bravo Uniform said:
You have bug guts in your pitot from hours of flying. Your mechanic will disconnect and run a wire through to clean out the crud. You will be on your way, unless you damaged something trying to diagnose it.

-Diagnosed from the other end of the internet
Click to expand...

thanks for that confirmation, yeah it seems like that may be it. during training you learn so much about clogged statics and pitot's but never had anything happen in 10 years of flying. ok I'll leave it alone and work with a mechanic to clean it out. seems like from @Jeff767 this does happen to grab a bug on the way! first time for everything I guess :)

thanks for all the guidance folks, very much appreciated!
 
oh sorry one more Q @455 Bravo Uniform, @Rgbeard and @Jeff767 : while it appears than to be common that grabbing a bug is common, would the debris stay within the pitot mast or would it still be "alive" and crawl up the tubes?

was wondering here since the tubes are relatively large(r) compared to the holes in the mast hence if a bug through such a small hole can actually clog the tube or be "stuck" in the curve from intake to upward area.
 
xander75 said:
oh sorry one more Q @455 Bravo Uniform, @Rgbeard and @Jeff767 : while it appears than to be common that grabbing a bug is common, would the debris stay within the pitot mast or would it still be "alive" and crawl up the tubes?

was wondering here since the tubes are relatively large(r) compared to the holes in the mast hence if a bug through such a small hole can actually clog the tube or be "stuck" in the curve from intake to upward area.
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Doubtful, but there’s only one way to find out… Hard to diagnose without removal and inspection.
 
Does your Arrow have the pitot drain valves between the pilot's seat and bulkhead at the floor? A plug of water could be the culprit.
 
I think you have a clogged pitot. I normally remove them and blow air backwards into a cloth to catch the junk. Then I flush cleaner few times to make sure it’s all clear.

Here’s a “after I broke out” pic of of my instruments when took a hit right in the pitot. It was a year ago while on approach in IMC. Happened right when I put the gear down. Autopilot was coupled. The airspeed slowly started decreasing. I did the wrong thing and began adding power bc I thought I was getting slow. After loosing 40 knots I thought I was going to stall. Then I screwed up again and accidentally touched the GA button on the yoke while trying to disconnect the autopilot. Then the display X’d out because of pitot source loss. The airspeed then rapidly fell to zero and it became obvious that I had a failed system.
Lessons learned:
-Always keep the pitot covered when not flying. This didn’t cause my problem but I’m protecting the best I can nowadays.
-Always be ready to fly known pitch and power. I did this alright, but I waited too long before transitioning to known numbers.
-NEVER put the damn GA button on the yoke (previous owner).
 

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When that happened to me I was flying my Cessna A185E floatplane and landed in Victoria for customs. I took the pitot head off and needed something to route out the hole.

JUST THEN a seagull feather drifted by on the water. I picked it up, and cut it with my survival knife at an angle. It turned out to be JUST the perfect tool to clean out the line. It was even the right consistency and sharp.

Stuck it in the glove box.............it was even light weight!!
 
Dan Thomas said:
Exactly. Those instruments are designed to react to very small pressures, and more than one pilot has ruined expensive stuff by blowing and sucking on the pitot or static ports.

Mechanics might be expensive, but doing your own troubleshooting and repairs without knowing what you're doing is a LOT more expensive.

I have heard auto mechanics say that Youtube is the best thing ever for them. It results in lots of business for the car repair shops, fixing or replacing stuff the owner busted as he tackled the job, guided by Youtube "experts."
Click to expand...

I had an ASI acting strange on a plane I owned years ago. Somehow when washing the plane I had gotten a small slug of water in the pitot line. Removing the line at the ASI and blowing out the line fixed the issue.

Dan is correct that mechanics are many times cheaper because they can prevent the owner from either doing more damage, or spending a bunch of money throwing parts at a problem.

Years ago a man brought his car in for service to the auto shop. Said it was running extremely rich. As the mechanic was looking at it the owner admitted to attaching a 12 volt lead to a wire coming from the harness that was not connected to anything. Upon hearing this the mechanic informed the owner that the onboard ECM computer would need to be replaced. The man asked how the mechanic would know that. The mechanic explained that the wire he connected the voltage to was there for testing the ECM and that what he had done shorted/destroyed the ECM.
 
Domenick said:
Does your Arrow have the pitot drain valves between the pilot's seat and bulkhead at the floor? A plug of water could be the culprit.
Click to expand...
I'd need to check, I never noticed the valves, but it seems they are a bit hidden besides the seat, so lemme check that also!
 
hi folks, wanted to share the root cause of the situation that i had...!

in the end it was not a clogged pitot but a t-splitter in the cockpit for the pitot that shares the pressure between the ASI and the ASPEN apparently snapped...
I discovered this as i took the approach suggested by some of you fine folks above, to trace and blow it out from the cockpit when i found this tube hanging loose.
it seems like from tube bending pressure and the switch from low temps to high temps this piece of plastic decided to give up. it matches the symptoms of the pitot intake "leaking" ( yeah no kidding ) and both instruments not operational.

the other neat part is that apparently the tubing for this is similar to fuel lines for cars, so you can pick up these t-splitters from the autozone easily!
although the $7 package has much more than you need it has a few nice spare parts...
https://contentinfo.autozone.com/znetcs/product-info/en/US/drm/47329/image/1/

see here the situation i had:
https://drive.google.com/file/d/1vTyo4Uood6-vNJnsZWz6HouVTuXgfyz1/view?usp=sharing

few more learnings i had:
1) i also verified with various avionics shops that using syringe on the tubes to verify operation is exactly what they do also, with the only mention for the static test to do it slowly to not overwhelm the VSI.
2) a (home) fan in front of the pitot doesnt make the ASI move
3) blowing an inch away from the tube with your lips moves the ASI to about 40-60 and is a good and safe test to do.
4) this arrow ii i have doesnt have the drains hinted on by @Domenick (as it was explained by shops it would drain out of the special drain hole of the pitot on the wing)

just wanted to pass on some experiences if it helps anyone!
 
xander75 said:
hi folks, wanted to share the root cause of the situation that i had...!

in the end it was not a clogged pitot but a t-splitter in the cockpit for the pitot that shares the pressure between the ASI and the ASPEN apparently snapped...
I discovered this as i took the approach suggested by some of you fine folks above, to trace and blow it out from the cockpit when i found this tube hanging loose.
it seems like from tube bending pressure and the switch from low temps to high temps this piece of plastic decided to give up. it matches the symptoms of the pitot intake "leaking" ( yeah no kidding ) and both instruments not operational.

the other neat part is that apparently the tubing for this is similar to fuel lines for cars, so you can pick up these t-splitters from the autozone easily!
although the $7 package has much more than you need it has a few nice spare parts...
https://contentinfo.autozone.com/znetcs/product-info/en/US/drm/47329/image/1/

see here the situation i had:
https://drive.google.com/file/d/1vTyo4Uood6-vNJnsZWz6HouVTuXgfyz1/view?usp=sharing

few more learnings i had:
1) i also verified with various avionics shops that using syringe on the tubes to verify operation is exactly what they do also, with the only mention for the static test to do it slowly to not overwhelm the VSI.
2) a (home) fan in front of the pitot doesnt make the ASI move
3) blowing an inch away from the tube with your lips moves the ASI to about 40-60 and is a good and safe test to do.
4) this arrow ii i have doesnt have the drains hinted on by @Domenick (as it was explained by shops it would drain out of the special drain hole of the pitot on the wing)

just wanted to pass on some experiences if it helps anyone!
Click to expand...

Welcome to airplane ownership. Many things work fine one day, and the next day they don’t. It’s good on your part to want to learn how to fix things. But I would suggest next time trouble shoot with a A&P. As other have said it is easy to mess something up more than it was by just pulling things apart.
 
oh hey totally @TommyG ! it is easier to fix a car on the road than a plane in the sky! and totally agree on proper guidance, fortunately, I had him on facetime and text to verify/validate. so all good there.

thanks for all the solid responses and considerations btw, this is really a great forum to be part of...!!
 
You're not done yet. That piece you bought at AutoZone does not legally belong in your airplane. It may appear the same but it's not. If it is, then you have bigger problems and probably caused the failure in the first place. Not only that but you now have to have your pitot system re-certified as well. Anytime you break a line open weather you replace a line or an indicator it has to be re-certified and a logbook entry by a certified mechanic. My suggestion would be to get your avionics shop that does your inspection to sign off the connector repair.
 
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