Cherokee/Arrow Alt Static Source Surprise

[ArrowFlyer86]

I have this placard that sits right above my left knee on the panel when I'm in the pilot seat of the arrow:


I've always interpreted this to mean: "if you need an alternate static source, pull the little lever aft and it'll open"

I check to make sure my static port is clear each preflight and I don't fly in icing conditions, thus I've never had a clogged external static port/reason to use an alternate static source in a flight. That means all of the flight time since buying the airplane 4y ago I've left the switch in the forward position (it's a little valve with a lever on the side that can be rotated 90 degrees so that it points backwards towards the pilot [pulled aft] or is sideways pointing towards the LH wing [pushed forward]).

Forward position:


Aft position:


It wasn't until today that I was using it on a XC flight, mainly b/c it was a long, uneventful trek and I toggled it wanting to see the expected behavior for funsies.
But everything was reversed. When pulled AFT vents/heat/defroster don't do anything, but when forward they make an impact. A short lived impact to be sure, but an impact nonetheless.
It's the kind of impact I wouldn't normally see in air (VFR flying) unless I turned the vents from OFF to maximum blast at once and watched my VSI in the interim, which I did on this flight. On the ground I verified it as well by shutting the door quickly and watching the VSI.

So that was an interesting development. I'll admit, I never thought to test and make sure it wasn't reversed. Kind of like I wouldn't normally think my Alternate Air is wired in reverse for OPEN/CLOSE but maybe I should check that too! lol.
During 4 annuals, G5 AI install, a static line repair and 2 IFR equipment signoffs, no one's ever mentioned it. I've flown hundreds of flights on FF verifying my altitude without issue to ATC and everything, so thankfully any deviation wasn't significant.

I'm curious... Anyone else here ever tested theirs and found this? I found one other case online here. So maybe it's not completely without precedent, but embarrassing nonetheless. I figure I either need a new placard or need the plumbing to be corrected. A third option is possible: I'm completely obtuse and the placard is correct and my entire understanding of what "pull aft to open" means is wrong lol.

 

[Dan Thomas]

I have this placard that sits right above my left knee on the panel when I'm in the pilot seat of the arrow:
View attachment 132390

I've always interpreted this to mean: "if you need an alternate static source, pull the little lever aft and it'll open"

I check to make sure my static port is clear each preflight and I don't fly in icing conditions, thus I've never had a clogged external static port/reason to use an alternate static source in a flight. That means all of the flight time since buying the airplane 4y ago I've left the switch in the forward position (it's a little valve with a lever on the side that can be rotated 90 degrees so that it points backwards towards the pilot [pulled aft] or is sideways pointing towards the LH wing [pushed forward]).

Forward position:
View attachment 132392

Aft position:
View attachment 132393

It wasn't until today that I was using it on a XC flight, mainly b/c it was a long, uneventful trek and I toggled it wanting to see the expected behavior for funsies.
But everything was reversed. When pulled AFT vents/heat/defroster don't do anything, but when forward they make an impact. A short lived impact to be sure, but an impact nonetheless.
It's the kind of impact I wouldn't normally see in air (VFR flying) unless I turned the vents from OFF to maximum blast at once and watched my VSI in the interim, which I did on this flight. On the ground I verified it as well by shutting the door quickly and watching the VSI.

So that was an interesting development. I'll admit, I never thought to test and make sure it wasn't reversed. Kind of like I wouldn't normally think my Alternate Air is wired in reverse for OPEN/CLOSE but maybe I should check that too! lol.
During 4 annuals, G5 AI install, a static line repair and 2 IFR equipment signoffs, no one's ever mentioned it. I've flown hundreds of flights on FF verifying my altitude without issue to ATC and everything, so thankfully any deviation wasn't significant.

I'm curious... Anyone else here ever tested theirs and found this? I found one other case online here. So maybe it's not completely without precedent, but embarrassing nonetheless. I figure I either need a new placard or need the plumbing to be corrected. A third option is possible: I'm completely obtuse and the placard is correct and my entire understanding of what "pull aft to open" means is wrong lol.

Looks to me like the valve needs to be turned (tightened) into the plumbing another 90 degrees. Then pulling aft on it would open it. The way it is now, the action is reversed.

It's basically the same as this fuel sumping valve. The valve is open when it is turned counterclockwise. That lifts the rubber seal off the seat. See where the seal is here? On the seat. Closed.

 

[ArrowFlyer86]

Looks to me like the valve needs to be turned (tightened) into the plumbing another 90 degrees. Then pulling aft on it would open it. The way it is now, the action is reversed.

It's basically the same as this fuel sumping valve. The valve is open when it is turned counterclockwise. That lifts the rubber seal off the seat. See where the seal is here? On the seat. Closed.

View attachment 132395

Do you think it could have loosened throughout time by 90 degs? Or more likely just installed at some point before with incorrect orientation? Feels like it's in there pretty snug to me and unlikely to move on its own.

Either way, if the solution is potentially just tightening it to get the right orientation that could be a nice, simple fix

 

[MauleSkinner]

Do you think it could have loosened throughout time by 90 degs? Or more likely just installed at some point before with incorrect orientation? Feels like it's in there pretty snug to me and unlikely to move on its own.

Either way, if the solution is potentially just tightening it to get the right orientation that could be a nice, simple fix

Probably installed that way at the factory. I would think the production test flight checklist should catch that, but as fast as they were pumping out airplanes, it wouldn’t surprise me if something like that was missed.

 

[Capt. Geoffrey Thorpe]

I've flown hundreds of flights on FF verifying my altitude without issue to ATC and everything, so thankfully any deviation wasn't significant.

ATC has no way to know that your actual altitude is different than the altitude reported by transponder / ads-b (which will correlate to your altimeter). So, no matter how large the error, no one will be the wiser (unless you end up in the tree tops...)
But I don't see how an actual IFR transponder check could have passed with the valve open...

 

[MauleSkinner]

But I don't see how an actual IFR transponder check could have passed with the valve open...

Good point…

 

[Cap'n Jack]

Probably installed that way at the factory. I would think the production test flight checklist should catch that, but as fast as they were pumping out airplanes, it wouldn’t surprise me if something like that was missed.

Maybe it was outsourced to Boeing?

 

[ArrowFlyer86]

ATC has no way to know that your actual altitude is different than the altitude reported by transponder / ads-b (which will correlate to your altimeter). So, no matter how large the error, no one will be the wiser (unless you end up in the tree tops...)
But I don't see how an actual IFR transponder check could have passed with the valve open...

Sorry brain fart on my behalf. You're right!

 

[Dan Thomas]

Probably installed that way at the factory. I would think the production test flight checklist should catch that, but as fast as they were pumping out airplanes, it wouldn’t surprise me if something like that was missed.

It wasn't like that when the airplane was built. Perhaps the seal on the original valve deteriorated and someone replaced the valve, and it got tight at that spot so they left it. You might damage something by tightening it further, especially if they used a hardening sealer on the threads.

The seal on that valve might be shot anyway. A new valve with the long, one-sided lever might be awfully expensive. It would likely be a Piper part. I'd see if there was a standard MS O-ring that fit. Lots of those older valves used an MS28775-006 O-ring, but that one might be a hair bigger, maybe an -007. An MS29513 series would work, too. That series was for fuel, the MS28775 was for hydraulics. MS28778 was for static seals. It's only sealing air, of microscopic pressures, so any of them that fit would work.

The Cessna valve was a purpose-built valve that sure wasn't cheap. It was a push-pull affair. It had some threaded ports for the static lines, and just a small hole in the side of the valve body for the vent. Cessna had a service bulletin (which soon became an AD) warning that folks in the factory had been putting the part number sticker over that tiny port so that the valve could not vent if necessary. https://www.federalregister.gov/doc...5-177-180-182-185-188-206-207-208-210-303-336

 

[Bell206]

A new valve with the long, one-sided lever might be awfully expensive. It would likely be a Piper part.

The valves are fairly cheap even the Piper P/N valves. If you use the standard spec number they're even cheaper.. Nothing like the Cessna alt air switches. Regardless, there are a number of 3rd party spec'd pneumatic switches out there that can also be used to replace those OEM switches as a minor alternation. Which is one way to replace those expensive Cessna alt air switches.




Item 19:


492-100:


CCA-7450:

 

[Dan Thomas]

The valves are fairly cheap even the Piper P/N valves. If you use the standard spec number they're even cheaper.. Nothing like the Cessna alt air switches. Regardless, there are a number of 3rd party spec'd pneumatic switches out there that can also be used to replace those OEM switches as a minor alternation. Which is one way to replace those expensive Cessna alt air switches.


View attachment 132416

Item 19:
View attachment 132413

492-100:
View attachment 132414

CCA-7450:
View attachment 132415

Can't complain about those prices. Cheaper than the labor to fix up an old one.