Whiskey compass don't like G's

Ed Haywood

Ed Haywood

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Big Ed
Did an aerobatic session today. After my sequence, I pointed for home and did my usual routine to get some fresh air and settle down a bit before landing.
I noticed a streak of fluid on the inside of the windshield. I touched it and it was oily. I looked below it and there was a large puddle of fluid on the glare shield.
That area is directly above the header tank, so alarm bells went off. I started feeling under the panel for leaks, ran through the mental checklist for a cockpit fire, and sniffed and tasted the fluid.
After about 30 seconds, I settled down and realized the obvious. It was mineral oil from the compass. A lot of it. Like, probably all of it.
I guess those old seals really didn't like negative G's. Or maybe positive G's. Anyhow, it was a bit odd, since I have at least a hundred hours of acro on this plane.
Picture for your enjoyment. Most of the fluid dried out by the time I took it.
So how do you all want to spend my money ... new seal kit or vertical card compass?
PXL_20240616_191408382.jpg
 
Ed Haywood said:
new seal kit or vertical card compass?
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New seal kit. Card compasses tend to be very sensitive in some installs and aircraft. I've replaced more card compasses with a mag compass than the reverse. Perhaps talk to some other acro buddies on that side of the equation?
 
Ed Haywood said:
new seal kit or vertical card compass?
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I'm told that if a shop is doing the work, installing an Airpath seal kit is not much less cost than installing whole new Airpath compass. I'm also told that the Airpath is vulnerable because the sun beats down on the parts of the compass with the rubber seals holding in the fluid and that a SIRS compass will probably last an owner's lifetime because it somehow doesn't have the same weakness.
 
asicer said:
I'm told that if a shop is doing the work, installing an Airpath seal kit is not much less cost than installing whole new Airpath compass. I'm also told that the Airpath is vulnerable because the sun beats down on the parts of the compass with the rubber seals holding in the fluid and that a SIRS compass will probably last an owner's lifetime because it somehow doesn't have the same weakness.
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Just guessing here, so this is just my opinion, its possible you were told, may be by a shop that has to pay employees and the rent. Air path seal kit expensive ? Not so!! may be 20 to 30 bucks, takes less than an hour to repair, (we used pay about $14 about 5 years ago. As the post above i replaced more vertical card compasses and recommended repair of Air Path. not much can go wrong with the whisky type other than the leak when its neglected over time. placement can be an issue but same with the vertical card. usually people like the vertical type because its to hard for them to learn / get used of reading them. The vertical card will stick after a while, if you ever seen inside one you would be amazed to find out practically nothing inside. two gears a heavy wheel with magnets. the gears wear and the filings (ferrous) from the wear get suck in the gear teeth, no repair is available (i checked with the manufacture, you have to buy a new one). One customer went thru 3 before he gave up and got an air path. You just about never have to buy a new one just reseal. Never tracked the average time between resealing but i have one in my plane and its been about 8 or 9 years, still good, no leaks, no fluid ! ,, just kidding still has the kerosene.
 
kyleb said:
What if you just left the fluid out until the next annual?
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I know people don't like to hear about regs, but check out 91.205 (i think thats it) to be legal its required to operate. i guess for the children of the magenta line, they are covered with a magnetometer.
 
Dave Palacios said:
I know people don't like to hear about regs, but check out 91.205 (i think thats it) to be legal its required to operate. i guess for the children of the magenta line, they are covered with a magnetometer.
Click to expand...

Well, if we’re going to get all regulatory about it, stick one of these on the glare shield and buy an A&P a beer to call it a minor alteration...
;)

 
asicer said:
I'm told that if a shop is doing the work, installing an Airpath seal kit is not much less cost than installing whole new Airpath compass.
Click to expand...

I'll do it myself, under supervision, so only cost is parts.
 
Ok, I was asked on my single engine commercial checkride...''How do you know when the compass is empty of whiskey.??''

I thought for a second and answered, ''Well, the card will be leaning to one side and it won't move...''

''Nope, incorrect. The whiskey will be all over the glare shield...'' said the DPE.

Now I know he was right.

And he asked me that question to try to get me to relax with a little humor...
 
Note that resealing a Compass is not a task for an A & P or most

Repair Stations. It requires an INSTRUMENT Repair Station to do the job.

There have been Techs that did this and were dumb enough to log it!
 
nauga said:
91.205 doesn't even stipulate it must be a compass.

Nauga,
boxed in and out
Click to expand...

I pulled that thread. Here's a useful article.

TLDR: part 23 also matters for certified aircraft. For a while, part 23 said "magnetic compass". After 2012 it was changed to match part 91. That is relevant because in many cases the TC specifications will say "magnetic compass" or similar. The required equipment list in my AFM says "Airpath Compass".

I tried to analyze whether replacing a magnetic compass with a magnetometer would be a major or minor alteration, but concluded it exceeded my understanding. Either way, some sort of data would be required to establish that the magnetometer meets the original TC requirement.

That's where it gets a bit sticky. I have an AV-30C with magnetometer, and it works great. The STC states that the magnetic compass must remain installed. I found internet comments saying the same about the G5, though I did not read the STC to confirm. So some other path would have to be found.
 
Currently going down the rabbit hole on legality of topping off compass fluid and/or resealing. Thanks as always to @Bell206 for wise advice. Favorite internet comment thus far:

The compass fairy showed up and repaired a compass on a plane I once knew of. I haven't been able to catch her in the act yet. Unfortunately she never makes logbook entries. If I do catch her, I'll definitely dump the new fluid out and put the leaky gaskets back in, for safety.
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One interesting line of thought would be to apply the FAA definition of preventative maintenance: “simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.”

That raises a question I have not seen directly addressed before: FAA Coleal memo says Appendix A to Part 43 provides examples of owner PM, not an exhaustive list. Say an owner makes a good faith interpretation that something is owner PM, but gets it wrong. What are the consequences? Loss of pilot cert? Aircraft unairworthy until corrected?
 
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Half Fast said:
Just installed? Does it say there has to be whiskey in the jar?
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Actual wording on the AV-30C is "a wet compass, or magnetic direction indicator, must be installed in the aircraft."

As certification required equipment, it cannot be placarded or removed. So I suppose it depends on whether a dry compass is inoperative, which I think is probably the case.
 
Ed Haywood said:
Say an owner makes a good faith interpretation that something is owner PM, but gets it wrong. What are the consequences? Loss of pilot cert? Aircraft unairworthy until corrected?
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That’s a good question and I’d love to hear about any actual cases.

By the way, did you know you only have to retain maintenance records for 12 months? Isn’t that interesting?
 
The Hamilton vertical card compasses are extremely sensitive to vibration, so they have a really soft mounting to isolate them from the airframe. One can spend a LOT of time trying to make the thing work if that mounting isn't soft.


The magnetic compass, like the magnetos, doesn't need power from the airframe's electrical system. In Canada the law is specific on this:

605.14 No person shall conduct a take-off in a power-driven aircraft for the purpose of day VFR flight unless it is equipped with
<snip>
  • (d) a magnetic compass or a magnetic direction indicator that operates independently of the aircraft electrical generating system;

There are vast areas of Canada that have no cellphone service. There are lots of airplanes with magnetometers and GPS and pilots with handheld GPS, but every one of them relies on the ship's power or its batteries. So the feds keep this requirement, since it's all you have if you're over remote territory, especially if you're in IMC and everything dies except the vacuum gyros. Another law requires the annual calibration of that compass. As with the US, most don't take any of this very seriously. And almost all of them are flying close to urban areas. Many of them seem to never have been off the city sidewalks and have no idea of the vast silences out there. Population density in North America:

1718643102075.png

You do know which area is Canada, right?
 
Ed Haywood said:
Currently going down the rabbit hole on legality of topping off compass fluid. Thanks as always to @Bell206 for wise advice. Favorite internet comment thus far:



One interesting line of thought would be to apply the FAA definition of preventative maintenance: “simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.”

That raises a question I have not seen directly addressed before: FAA Coleal memo says Appendix A to Part 43 provides examples of owner PM, not an exhaustive list. Say an owner makes a good faith interpretation that something is owner PM, but gets it wrong. What are the consequences? Loss of pilot cert? Aircraft unairworthy until corrected?
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Mike Busch did a Webinar for EAA Preventative Maintenance for Owners. If you're a Member it is on the website. He discussed the difference between what the FAA Specifically lists and other examples that are "like those".
 
whatever it is, in the context of a recreational owner, I'd hope it'd be a severe punishment outsized of the infraction. The only way we'll get more people to abandon the space and internalize the absurdity behind criminalizing the same action EABers are allowed to flaunt in plain sight, is to finally scald the frog all at once via equally absurd punishments.

But that's me and my accelerationist desires for this space. As someone whose other hobby during my ownership tenure was hangar beekeeping, I always shrugged my shoulders on this. odin knows I've been called worse than scofflaw in this life.
 
Dan Thomas said:
You do know which area is Canada, right?
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The area that is 3.4 miles due east from my house? (That kind of map is always interesting...)
X3 Skier said:
Mike Busch did a Webinar for EAA Preventative Maintenance for Owners.
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And worth a watch IMO... Mike references the Coleal letter that kinda says that the list of preventative maintenance in appendix whatever is not exhaustive.

 
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Dan Thomas said:
The Hamilton vertical card compasses are extremely sensitive to vibration, so they have a really soft mounting to isolate them from the airframe. One can spend a LOT of time trying to make the thing work if that mounting isn't soft.
Click to expand...

I'm leery of how well a vertical card compass would hold up under regular aerobatics.
 
www.aircraftspruce.com

COMPASS REPAIR W/FLUID | Aircraft Spruce

COMPASS REPAIR W/FLUID Airpath compass repair kits. Kit consists of diaphragm, 1/2 of compass fluid and face glass gasket.
www.aircraftspruce.com www.aircraftspruce.com

I found that the need for a wide mouth glass jar, to immerse the compass in - as the best way to tease the air out. Any bubbles will expand enormously and lead to seal failure in the 150° glareshield environment.
I have a pint of the fluid that I will never use, as my compass does not have fluid. Looks like buying from Spruce will be cheaper than me shipping it to you.
 
Half Fast said:
That’s a good question and I’d love to hear about any actual cases.

By the way, did you know you only have to retain maintenance records for 12 months? Isn’t that interesting?
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Have fun convincing a buyer of that when you try to sell it.
 
Ed Haywood said:
Say an owner makes a good faith interpretation that something is owner PM, but gets it wrong. What are the consequences? Loss of pilot cert? Aircraft unairworthy until corrected?
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Depends. If the FAA is the one to note it like during a ramp check then they have the burden of proof your work is not correct. Same for an A&P. However, the majority of pushback usually comes from an IA during an annual inspection where they may not agree with your interpretation. I've had similar issues with some alterations I've performed.

As to the consequences not much if you followed the rules and thought your work was correct. Again it depends on the specifics. For the IA, he may not want to sign the annual unless whatever was performed is corrected to his satisfaction. Regardless, if you make a determination that the task fits the definition of prevent mx and also "fits" into one of the 31 categories in Appx A(c) and you complete the required record, go for it. And the more reference you have to perform the work the better your stance will be.

However, the issue for working on a mag compass its whether it is considered an instrument per the Part 1 definition. Most guidance state it is an instrument so it doesn't fall under prevent mx even for servicing. And as mentioned above, per Part 65 even an A&P cannot perform repairs or alterations to instruments which replacing leaking seals would be considered a repair. However, servicing is not considered a repair in most circumstances so I'm of the opinion an A&P can service a mag compass.
Ed Haywood said:
I'm leery of how well a vertical card compass would hold up under regular aerobatics.
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I would talk to some of your aero buddies. As noted, I wouldn't think it would last long in that environment in my experience. But I dont know for sure.
 
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