Leaky wet compass

AuntPeggy

AuntPeggy

Final Approach
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On our trip to California (after replacing a tire) we noticed that the wet compass was about half empty. (In this case, not half full as we considered optimism irrelevant.) It was daylight, we were heading into mountainous regions and cloudy skies where we would need to file IFR to continue. So we found a field with a mechanic and requested a fix. He had the proper fluid but not the kit with the gaskets, etc. About that time, someone in the hangar who was wearing a spiffy leather flight jacket covered with colorful patches challenged the decision. "Do you have a handheld GPS? Is it a safety of flight issue?"

We have a panel mounted Garmin IFR 530 GPS with WAAS and terrain and a separate GPS attached to our computer that receives XM WX and displays terrain. So we opted to wait overnight for delivery of the kit and opted not to debate the issue. As it turned out, it took two nights because of the Christmas rush.

Our reasoning is that the wet compass is required for IFR flight. Do you agree?
 
Some body needs to read 65.81

(a) A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95.

Is your compass a required instrument?

I know, I know, he was the compass fairy
 
Tom-D said:
Some body needs to read 65.81

(a) A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95.

Is your compass a required instrument?

I know, I know, he was the compass fairy
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I had that very same discussion with a local A&P-IA a couple of years ago.

"Sure, I can fix it -- but I think I have to be an avionics tech to do a compass..."
 
dmccormack said:
I had that very same discussion with a local A&P-IA a couple of years ago.

"Sure, I can fix it -- but I think I have to be an avionics tech to do a compass..."
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he needs to be an authorized instrument repair facility.

no discussion required, it is written very clearly..
 
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All of these new toys are wonderful until the power goes out. We learned partial panel for a good reason. You did the right thing.
 
deltafox said:
All of these new toys are wonderful until the power goes out. We learned partial panel for a good reason. You did the right thing.
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I agree, wise choice. Regardless of how many cool toys are on board, the compass is required.

That being said, maybe you should have bought the whiskey compass a drink and got it loaded ?!?!
 
AuntPeggy said:
On our trip to California (after replacing a tire) we noticed that the wet compass was about half empty. (In this case, not half full as we considered optimism irrelevant.) It was daylight, we were heading into mountainous regions and cloudy skies where we would need to file IFR to continue. So we found a field with a mechanic and requested a fix. He had the proper fluid but not the kit with the gaskets, etc. About that time, someone in the hangar who was wearing a spiffy leather flight jacket covered with colorful patches challenged the decision. "Do you have a handheld GPS? Is it a safety of flight issue?"
Click to expand...

Maybe you should have asked him exactly where on a GPS you can read your HEADING.

Good call to get it fixed. I've done the same, getting an "emergency" compass repair away from the home field.
 
You didn't trust the spiffy leather flight jacket guy (note I did not say Pilot) I don't understand why. LOL Good Call.
 
So ... was it fixed by a mechanic or an authorized avionics shop?

I have had less than good luck repairing compasses. Always had to buy a new one shortly thereafter. Maybe I need to find better avionics shops.
 
Ken Ibold said:
So ... was it fixed by a mechanic or an authorized avionics shop?

I have had less than good luck repairing compasses. Always had to buy a new one shortly thereafter. Maybe I need to find better avionics shops.
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I had mine refilled right after I bought the airplane and it's been floating along merrily since then (14 months)
 
deltafox said:
All of these new toys are wonderful until the power goes out. We learned partial panel for a good reason. You did the right thing.
Click to expand...

flyingcheesehead said:
Maybe you should have asked him exactly where on a GPS you can read your HEADING.

Good call to get it fixed. I've done the same, getting an "emergency" compass repair away from the home field.
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These responses come closest to answering the question, "Is it a safety of flight issue?"

My thoughts were that I can use all those expensive electronics to navigate from one place to another until the fateful moment when the voice on the radio says "turn to heading ... traffic avoidance." If my compass isn't reliable, my heading indicator isn't reliable and I cannot comply reliably.

You are all much more understanding than my mother-in-law who was completely perplexed. "You were delayed for two days because of a compass? Like Boy Scouts use?"
 
dmccormack said:
Perhaps under the HDG field on the 430?
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Doesn't that indicate the suggested heading to the next waypoint without regard for wind? I know that I try to get TRK to match HDG even when it is off by as much as 20* from the reading on the heading indicator. When they match, I move the heading bug to the location of the heading indicator needle without regard for the actual HDG number. [edit] After first resetting the heading indicator to match the compass.[/edit]
 
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AuntPeggy said:
You are all much more understanding than my mother-in-law who was completely perplexed. "You were delayed for two days because of a compass? Like Boy Scouts use?"
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Now that was funny. :cornut:
 
Tom-D said:
Some body needs to read 65.81

(a) A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95.

Is your compass a required instrument?

I know, I know, he was the compass fairy
Click to expand...

The mechanic removed the compass, sent it to a repair station authorized to perform the repair, and reinstalled it on the aircraft when it was returned with an 8130 and performed a compass swing and updated the compass card. He then provided a sticky with an appropriate log book entry signed by him along with the copy of the 8130 for Peggy's log book, or something like that.:thumbsup:
 
John Collins said:
The mechanic removed the compass, sent it to a repair station authorized to perform the repair, and reinstalled it on the aircraft when it was returned with an 8130 and performed a compass swing and updated the compass card. He then provided a sticky with an appropriate log book entry signed by him along with the copy of the 8130 for Peggy's log book, or something like that.:thumbsup:
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That's great,,,,,, the compass fairy works for me. :)
 
dmccormack said:
Are we talking VFR or IFR here...?
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Does it matter? She's heading to California and is probably gonna run into some airspace where she'll need to be talking to NorCal and/or SoCal and may be vectored for sequence or traffic.
 
flyingcheesehead said:
Does it matter? She's heading to California and is probably gonna run into some airspace where she'll need to be talking to NorCal and/or SoCal and may be vectored for sequence or traffic.
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I wasn't suggesting she *not* get the compass fixed.

Just that determining a heading from a GPS isn't all that tough, and available, in a pinch (would you immediately land if your compass started leaking en route?)
 
dmccormack said:
Yes, though you should be able to deduce desired heading from DTK and Actual Track.
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There is no way to determine the heading solely using the 430. You can determine the course. But the course is != to the heading. Controllers ask you to fly headings - not courses.

If a controller tells one aircraft to fly heading 180 and then asks you to fly heading 180 and you instead fly course 180 and there is a large crosswind you're not going to be tracking like the controller expected.
 
jesse said:
There is no way to determine the heading solely using the 430. You can determine the course. But the course is != to the heading. Controllers ask you to fly headings - not courses.

If a controller tells one aircraft to fly heading 180 and then asks you to fly heading 180 and you instead fly course 180 and there is a large crosswind you're not going to be tracking like the controller expected.
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Yes, there is a way, and while you may not achieve mathematical precision, you will be close enough for ATC work.

I'm not proposing this be SOP, but if your whiskey compass should die while flying IFR or in Class B or C or even VFR with Traffic Advisories, you have enough information on the 4/530, or 2/3/496 to comply with ATC headings until you reach your destination.

An immediate diversion to landing upon failure of the wet compass would be dumb.
 
dmccormack said:
Yes, there is a way, and while you may not achieve mathematical precision, you will be close enough for ATC work.

I'm not proposing this be SOP, but if your whiskey compass should die while flying IFR or in Class B or C or even VFR with Traffic Advisories, you have enough information on the 4/530, or 2/3/496 to comply with ATC headings until you reach your destination.

An immediate diversion to landing upon failure of the wet compass would be dumb.
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Once again there is no way to determine a heading. Please tell me how you determine a heading with a 430. You can determine the course - that is it.

Can you use a course to substitute for a heading in a pinch? Sure. But I'd tell ATC I was doing so. It's required equipment, it failed, and I have no other way to determine the heading. ATC is expecting me to be using heading and I can't do so. There is no reason to deceive them. Communicate the problem. (Except if you're Lance Fisher. He probably has like five or six ways to determine the heading in his Baron)
 
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Here's a silly question - was the whiskey compass just low on fluid, but still working, or was it's movement indeed impaired by the low fluid?
 
jesse said:
Once again there is no way to determine a heading. Please tell me how you determine a heading with a 430. You can determine the course - that is it.
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I agree that a GPS by itself does not provide a way to determine heading unless you are on the ground. In the air you could attempt to measure drift visually and combine that with GPS track but that would require ground contact.

(Except if you're Lance Fisher. He probably has like five or six ways to determine the heading in his Baron)
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Actually I only have two heading sources in the plane (slaved HSI and wet compass). The HSI heading does show up on several other displays but it's still only one raw data source. I suppose I do have a third in that my iPhone has a compass app but I've never used that in flight.
 
dmccormack said:
Yes, though you should be able to deduce desired heading from DTK and Actual Track.
Click to expand...

When DTK and TRK don't match, it's simply because the plane isn't traveling parallel to the current leg of the flight plan (or direct-to leg). Adding a crosswind from either direction won't change that as long as you maintain the same track.
 
Fearless Tower said:
Here's a silly question - was the whiskey compass just low on fluid, but still working, or was it's movement indeed impaired by the low fluid?
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Not a silly question. The compass was low on fluid, but still rotating. However, since the top of the fluid line intersected the middle of the markings, it was difficult to read the compass. There is a question also on the accuracy of the compass. I have no idea whether its movement was impaired due to the low fluid level and chose to believe it was.
 
gismo said:
I suppose I do have a third in that my iPhone has a compass app but I've never used that in flight.
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IME, it sucks.

Okay, maybe not. The first time I used it, it was way off - maybe ±30º. I just tried it again and it seems to be right on. Maybe they fixed it in a software update. :dunno:

I would sure like to make sure it works more reliably before using it in the plane though.
 
AuntPeggy said:
Not a silly question. The compass was low on fluid, but still rotating. However, since the top of the fluid line intersected the middle of the markings, it was difficult to read the compass. There is a question also on the accuracy of the compass. I have no idea whether its movement was impaired due to the low fluid level and chose to believe it was.
Click to expand...

Fair enough - if I was concerned about the ability to use read the compass and/or questioned it's accuracy, I too would want to get it repaired before launching into IMC.
 
Fearless Tower said:
Here's a silly question - was the whiskey compass just low on fluid, but still working, or was it's movement indeed impaired by the low fluid?
Click to expand...

They will work just fine empty. but the fluid dampens the motion to make it easier to read.

The oil by definition is clear petroleum oil..... clear lamp oil at your local ACE hardware store.
 
flyingcheesehead said:
IME, it sucks.

Okay, maybe not. The first time I used it, it was way off - maybe ±30º. I just tried it again and it seems to be right on. Maybe they fixed it in a software update. :dunno:

I would sure like to make sure it works more reliably before using it in the plane though.
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Think about the tech in the phone for a sec. There's accelerometers, and a telco-network assisted GPS chipset. AFAIK there is no magnetic compass inside the iPhone. But I could be wrong. Easy to check... grab a magnet... get it close enough to have an effect, but don't fry the phone in the process. :)

Anyway... with the above assumptions, the iPhone needs *motion* for the GPS to register a direction and speed to the overlying software. (Actually the GPS just spits out a continuous stream of location, but I believe the Apple API internally does the math and will hand any App written to the API the direction and speed, all calculated.)

Most "Compass" Apps on iPhone merge the GPS data and the accelerometer data themselves. (I don't believe this is in the API, but I'd have to go research... I stopped looking at the Apple API's in iOS 3 days, 'cause I just didn't have time to code up what I wanted to code for the gadget.) Some do a sane job of it, some won't.

Mostly what I've seen is when the GPS data is showing little motion, the accelerometer is very heavily weighted in the math... for the person standing in one spot and "spinning around". If the phone had motion in a particular direction prior to the stopping and spinning, it's not bad. If you start at a dead standstill and spin around, where the "compass" will point is anyone's best guess. It's usually wrong.

In flight/vehicles it seems to weight the GPS data more heavily (appropriately) and the compass heading is accurate. Well... if you wanted true headings. (Of course, an App could offer a choice here... true or magnetic. Actually haven't seen one yet that does, but have only tried four and a couple of "dashboards".)

In general, it's just not a very good way to do it. But it kinda works well enough to fool most folks that it's accurate.

Additionally for pilots, the "assisted" part of all of this means that at high altitude, if the GPS chipset has to perform a warm start, or worse... a cold start... and needs help from the cell towers for finding an initial location... the compass is going to be quite wacky. Hopefully the API sends a warning that the GPS data is bad, but what do you bet most compass apps "coast" using only the accelerometer data when the GPS signal is unusable and flagged so in the datastream from the API? I bet lots.

To really get to the bottom of this, you'd need the API source code or definitions document, the source of the specific Compass App, and a really good Objective C code reader. Maybe not even a coder, just someone who could be really detailed in documentation of all the failure modes, and what the phone is actually using for input data at any one time.

Bonus points for someone who writes an App that shares the status of all the inputs as data points in the corners of the screen, calculates an "accuracy score" (arbitrary, but it's better than nothing) and then publishes real-world test data for accuracy against known headings.

Probably not going to get that level of software development for $0.99 a copy, unless someone's passionate enough about their Compass App that they add all of that over time, for free. :D
 
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