Magnetic Compass

Notatestpilot

Notatestpilot

Pre-takeoff checklist
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Aug 31, 2020
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Notatestpilot
I’ve had the same compass in my RV6 for close to twenty years now.
During the last couple flights I noticed it’s heading being off by 30 degrees from what my Dynon EFIS is showing.
Is it time to replace the magnetic compass?
 
How do you know it's the compass that's off and not the EFIS?
 
Notatestpilot said:
Is it time to replace the magnetic compass?
Click to expand...
Is the heading stable or does it wander?
Any recent electrical/avionics work performed?
Does the compass have enough fluid?
Maybe perform a compass swing?
 
Notatestpilot said:
I’ve had the same compass in my RV6 for close to twenty years now.
During the last couple flights I noticed it’s heading being off by 30 degrees from what my Dynon EFIS is showing.
Is it time to replace the magnetic compass?
Click to expand...
What's a compass? ;)
 

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Take the golf clubs out of the airplane?

Stop using a magnetic tipped screwdriver and steel screws in the areas sensitive to magnetic disturbance?
 
I've not done anything over or around the compass in nearly 20 years.
I'll try the compass swing first and see if it helps.
 
I should just remove the compass all together.
I already have the EFIS, the Garmin and the Foreflight in ipad....don't think I will be lost.
LoL!
 
Notatestpilot said:
I should just remove the compass all together.
I already have the EFIS, the Garmin and the Foreflight in ipad....don't think I will be lost.
Click to expand...
Do "the Garmin" and Foreflight give you mag heading as well? If so, do they agree with the Dynon, the compass, or neither?

If you're not sure which one is correct, do yourself a favor and do a compass swing. If you haven't changed anything that affects the mag field in the vicinity of the compass it's not likely to drift at an appreciable on its own.

Nauga,
who likes to know where he's headed
 
Notatestpilot said:
I'm going to do a compass swing first...
Click to expand...


That’s the easiest and cheapest 1st step. Please repost with your results. It will be interesting to find out how far off you find it.
 
brcase said:
Might also remove the compass from the aircraft and swing it by itself. Is the problem the compass or something else?
Click to expand...
A compass swing doesn't need to be particularly rigorous to see if you've got a 30 deg error. Seems to me the first order of business is to do a swing with everything in and on to see which "magnetic direction indicators" are accurate and which are not, then start troubleshooting the ones that are inaccurate.

I'd bet on a magnetometer issue over a 30 deg drift in a mag compass in a short period of time with no physical changes near the compass.

Nauga,
who used to be a swinger
 
You still are a swinger, just by the tail now?
 
Bought a new compass several months back, but never could get it to compensate properly. Ran out of "travel" on the E-W adjustment screws, and get clicking sounds. N-S worked just fine.

Since my airplane is made out of wood, I just tape a camping-type compass to the turtledeck for the reference during the swinging.

1697504971121.png

Will just re-install the old compass, next time I have the airplane apart.

Ron Wanttaja
 
Notatestpilot said:
I've not done anything over or around the compass in nearly 20 years.
I'll try the compass swing first and see if it helps.
Click to expand...
Personally, the only way I would remove a mechanical compass is if I had two electronic magnetic indicators with separate magnetometers and power sources.
 
Are there issues with the panel mount ones? Just seems like there could be, and I don't see many of them.
 
Skyrys62 said:
Are there issues with the panel mount ones? Just seems like there could be, and I don't see many of them.
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Not that I've seen but thats dated info. But back when I did avionics upgrades most people didn't want to give up limited panel space for a compass they wouldn't really use.
 
PaulS said:
New Cirrus' have been shipping without compasses for over a year now.
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Not to Canada.

Power-driven Aircraft — Day VFR​

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

  • (a) where the aircraft is operated in uncontrolled airspace, an altimeter;
  • (b) where the aircraft is operated in controlled airspace, a sensitive altimeter adjustable for barometric pressure;
  • (c) an airspeed indicator;
  • (d) a magnetic compass or a magnetic direction indicator that operates independently of the aircraft electrical generating system;
  • (e) a tachometer for each engine and for each propeller or rotor that has limiting speeds established by the manufacturer;
  • (f) an oil pressure indicator for each engine employing an oil pressure system;
 
I was just thinking about this the other day...to swing the compass I have to taxi across the airport to get on the compass rose. If I just remove the compass completely, I can move the convex mirror to the center of my dashboard and get a better view!
...rid of 1/4 pound of compass weight.
 
Part of my annual condition inspection on my experimental aircraft is to swing the compass on the compass rose and adjust it.

The imperfections are noted on the compass correction card.

Part of my takeoff procedure is to see the compass agrees with the runway heading as published in the chart supplement.

My compass is often in disagreement with my GPS because I am seldom pointed exactly in the direction of travel.
 
Notatestpilot said:
I was just thinking about this the other day...to swing the compass I have to taxi across the airport to get on the compass rose. If I just remove the compass completely, I can move the convex mirror to the center of my dashboard and get a better view!
...rid of 1/4 pound of compass weight.
Click to expand...
You may want to check the accuracy of the compass rose. Most of the ones on airport property are not much more than decoration, depending on how long ago they were constructed and where they are located. Mag north moves, some years more than others. If you are in the far north, that change can be pretty drastic.

Not saying to not use a compass rose, just suggesting to check it with a known good compass first. If you can find someone with a calibration compass, that would be ideal. But if you’re in the lower 48, the compass rose is most likely “close enough.”
 
aterry1067 said:
But if you’re in the lower 48, the compass rose is most likely “close enough.”
Click to expand...
FYI: it also needs to be calibrated every 2 or 5 years to be able to use for anything maintenance related. However, there are still some calibrated ones out there. A call to the tower or airport manager will let you know.
 
I find compasses any more have a habit of being way off. And compass Correction cards are frequently terrible. Well actually what I find is the that who ever made the compass correction card didn't bother to have the engine and radios running when they created it. I have seen several compasses that were 30 degrees off or more on certain headings with the engine running, where pretty good with it and the radios off..

I think a lot of VFR pilots just don't pay much attention to the compass, using GPS and the directional gyro's instead.

Not having a compass rose close by I have improved a few compasses by lining up on the runway heading. This should get me +/- 5 degrees accuracy. and setting the directional gyro. I then do a full circle stopping every 30 degrees to document the compass heading vs the DG. When I complete the 360 if the DG is working good I should be back on my original runway heading.
I can then either make adjustments to the compass and repeat, or just document it for the Compass Correction Card. Every time I have done this and taken it to the mechanic they just took may data and created a new compass correction card.

Brian
 
Dan Thomas said:
Not to Canada.

Power-driven Aircraft — Day VFR​

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

  • (a) where the aircraft is operated in uncontrolled airspace, an altimeter;
  • (b) where the aircraft is operated in controlled airspace, a sensitive altimeter adjustable for barometric pressure;
  • (c) an airspeed indicator;
  • (d) a magnetic compass or a magnetic direction indicator that operates independently of the aircraft electrical generating system;
  • (e) a tachometer for each engine and for each propeller or rotor that has limiting speeds established by the manufacturer;
  • (f) an oil pressure indicator for each engine employing an oil pressure system;
Click to expand...
My EFIS, AHRS and magnetometer had a backup battery which allowed it to operate "independently of the aircraft electrical generating system"
 
Bell206 said:
FYI: it also needs to be calibrated every 2 or 5 years to be able to use for anything maintenance related. However, there are still some calibrated ones out there. A call to the tower or airport manager will let you know.
Click to expand...


I remember reading that somewhere and thought it was ac 150/5300-13, but I didn’t see it after doing a cursory review.

The NGIA produces the WMM (World Magnetic Map) file every 5 years to account for the movement of magnetic north. In 2017 that location moved far enough that they issued an out-of-sequence file update. You can go to their website and find maps of magnetic declination around the globe; I know there is one where you can select a specific location and it gives you the most accurate declination data. I was really surprised at how far your compass can swing if you are flying around the mountains of Alaska or Canada…it can often swing as much as 30 degrees in just a few miles. To note, this file is what is used to create the isogonic lines on our aviation maps, and is used by lots of navigation components, especially in aircraft and ships.


World Magnetic Model (WMM)

The World Magnetic Model (WMM) is the standard model for navigation, attitude, and heading referencing systems using the geomagnetic field. Additional WMM uses include civilian applications, including navigation and heading systems.
www.ncei.noaa.gov www.ncei.noaa.gov
 
Notatestpilot said:
....During the last couple flights I noticed it’s heading being off by 30 degrees from what my Dynon EFIS is showing.
Click to expand...

Notatestpilot said:
I was just thinking about this the other day...to swing the compass I have to taxi across the airport to get on the compass rose....
Click to expand...

You don't need a compass rose to see if your mag compass is off by 30 deg. You can easily tell by checking a few headings against a handheld compass before dragging it across the field. If you're just looking for an excuse to remove it, remove it and be done with it.

Nauga,
regrettably
 
aterry1067 said:
thought it was ac 150/5300-13, but I didn’t see it after doing a cursory review.
Click to expand...
It should be in there. Cant get nothing to download at the moment but there should be an Appx which deals with compass rose calibration procedures. Its what we used years ago to have a rose calibrated by a local survey company but as I recall they coordinated it with the USGS vs NOAA.
 
The Cirrus TCDS allows the aircraft to operate without a wet compass..

The aircraft certification basis is amended to include the following regulation at the amendment level stated (Effective S/N 2238 and subsequent): (Note: The amended certification basis allows for the optional removal of the wet compass.)
 
Bell206 said:
Not that I've seen but thats dated info. But back when I did avionics upgrades most people didn't want to give up limited panel space for a compass they wouldn't really use.
Click to expand...
Unless things have changed, a compass is required. The pc12 ngx I flew had one, very frequently grossly off, but it had one.
 
Wagondriver said:
Unless things have changed, a compass is required. The pc12 ngx I flew had one, very frequently grossly off, but it had one.
Click to expand...
91.205 requires a “Magnetic Direction Indicator“, but that doesn’t have to be a traditional compass. For example, a magnetometer tied to an EFIS fills the requirement. It’s been worded that way for at least a decade.
 
tsts4 said:
91.205 requires a “Magnetic Direction Indicator“, but that doesn’t have to be a traditional compass. For example, a magnetometer tied to an EFIS fills the requirement. It’s been worded that way for at least a decade.
Click to expand...
How was it worded before?
 
tsts4 said:
91.205 requires a “Magnetic Direction Indicator“, but that doesn’t have to be a traditional compass. For example, a magnetometer tied to an EFIS fills the requirement. It’s been worded that way for at least a decade.
Click to expand...
But a TCDS may still require it, right?

And yes, I do see the EAB in your profile picture. :)
 
asicer said:
But a TCDS may still require it, right?

And yes, I do see the EAB in your profile picture. :)
Click to expand...
I suppose, but I’m no expert. My point was simply that part 91 doesn’t require it regardless of the certification category.
 
I like my old whisky compass. Its max deviation as installed in flight with engine running, radios on, etc. is never more than 1-2 degrees. I use it on every flight and it's worked reliably without maintenance for more than 15 years, has no firmware, doesn't need updates, doesn't rely on satellites, doesn't need electricity or batteries, doesn't freeze in the winter, nor melt in the summer, I can read it easily in any kind of light, and has no buttons I need to push.
 
My compass has some how stopped spinning when I cruise at 4500 feet. Can altitude affect the compass?
 
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