Swinging a Compass Using GPS and DG?

SoCal 182 Driver

SoCal 182 Driver

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SoCal 182 Driver
Friends -

A buddy was trying to explain to me how to use a plane's GPS and DG to swing a compass while on the ground, but he couldn't remember all the details. Has anyone done this? If so, can you provide me the procedure?

Thanks.
 
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Bell - Thanks for the info. I've edited my initial post. My buddy was describing an on-the-ground procedure, but he could not remember all of the details. (BTW, the Bell 206 series are my all-time favorite aircraft.)
 
Yes, you can do it on the ground.......and it is MUCH easier, faster, and more accurate than on a compass rose. Recommended by compass manufacturers.


""""""NOTE: If aircraft is equipped, GPS can be used (allow for deviation) to establish reference headings for compass compensation. This technique will eliminate possible errors caused by gyro precession."""""

[URL]http://www.airpathcompass.com/J30/index.php[/url]

 
I might’ve responded to this in another forum. Talk to some of your local avionics shops and inquire about them calibrating the compass and giving you a deviation card.

They will use a professional magnetometer to calibrate the compass, get you an accurate swing every 30°, print a deviation card, and get you the necessary logbook entry. The cost for me was an hour labor at $120. You’ll probably burn more than that in Av gas trying to calibrate by GPS in flight.

Since the compass was required equipment in my plane, just wanted to be sure everything was accurate and legal. I know there are other methods and ways to accomplish this, but working with my local avionics shop was the best solution for me.
 
You CAN'T be in flight for a GPS compass card swing. $120 is WAY too much for such a simple and quick procedure. 10 minutes MAX!!
 
I used a portable GPS to make two waypoints on an airport ramp, one directly south of the other. I then marked a N/S line on the pavement, followed by a perpendicular E/W line, and used those to swing my compass. Seemed to work well enough.
 
kgruber said:
You CAN'T be in flight for a GPS compass card swing. $120 is WAY too much for such a simple and quick procedure. 10 minutes MAX!!
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Actually nothing simple or quick about getting a deviation for every 30°. The simple act of turning the plane and lining it up precisely to get a reading is nearly an hour. Maybe 10 minutes if somebody’s trying to find north and assume the rest of the compass is accurate. Most compasses will deviate one, two, but likely 3-4°+or- off each 30° increment.
 
NordicDave said:
Actually nothing simple or quick about getting a deviation for every 30°. The simple act of turning the plane and lining it up precisely to get a reading is nearly an hour.
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You are IN the airplane and it is running and you are taxiing. Track 360, adjust.............. track 180 adjust.........track 270 adjust.........track 90 adjust, all with your GPS. It can even be a portable.

Repeat adjustments above.

Now track 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360 and jot down the corrections. There is no getting into and out of the airplane or drawing any lines on the ground.

Don't make such a quick, simple, and DEAD accurate procedure difficult. Remember that on the ground there is no "wind correction" because all movement is always track.
 
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Just give yourself a ‘swing’ when lined up for takeoff. Note the exact heading from the runway diagram, go with that.
 
kgruber said:
You CAN'T be in flight for a GPS compass card swing. $120 is WAY too much for such a simple and quick procedure. 10 minutes MAX!!
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It takes about an hour for me to do a swing on a King Air. From getting the paperwork started, to pulling the aircraft out, to getting the land compass and tools ready, to start and taxi out, to doing the work, taxi back, shut down, make new correction cards (one for the aircraft, one for the technical record), finish paperwork and bring aircraft back into hangar. It is all billable time and it ends up being at least an hour and half of that is with a second person sighting the aircraft while I run it and make adjustments.
 
FastEddieB said:
I used a portable GPS to make two waypoints on an airport ramp, one directly south of the other. I then marked a N/S line on the pavement, followed by a perpendicular E/W line, and used those to swing my compass. Seemed to work well enough.
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Once you have a N/S (or any known bearing), the rest is just math.
 
The hard part of doing it on the ground is maintaining a "level flight attitude". You need good progressive brakes and sufficient power to keep the tail up.
 
Bell206 said:
Curious. How do you mathematically adjust the compensating magnets in the compass prior to performing the swing?
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Huh? I was countering the Fast Eddies comments about setting two bearings up to do his compass swing. Once you set a N/S (or any other known line), You can easily mark the other cardinal points of interest (typically every 30 degrees) with simple math. Then you use that to do the same compass swing that an A&P would do on a regular compass rose.

In fact, you don't even need a GPS. You can generate survey points within the accuracy required with google maps or similar tools.

It isn't rocket science, well at least not to me, I spend over two decades and made my fortune developing high tech photogrammetry software for the intelligence community.
 
flyingron said:
Huh?
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FastEddie's post stated he marked the ramp and swung the compass. You replied: "Once you have a N/S (or any known bearing), the rest is just math." However, basic English implies once you determined a bearing you swung the compass mathmatically. Or did I misread it?
flyingron said:
In fact, you don't even need a GPS. You can generate survey points within the accuracy required with google maps or similar tools.
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Not quite. Unless you have an acceptable reference that states using Google, it can't be used at least for a TC'd aircraft. I've always used a master site compass which didn't require marking anything on the ramp and allowed a lot of flexibility.
flyingron said:
It isn't rocket science, well at least not to me .... and made my fortune...
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It's not rocket science to me neither. But I made my fortune actually performing compass swings and signing them off in the book.;)
 
kgruber said:
You CAN'T be in flight for a GPS compass card swing. $120 is WAY too much for such a simple and quick procedure. 10 minutes MAX!!
Click to expand...

kgruber said:
You are IN the airplane and it is running and you are taxiing. Track 360, adjust.............. track 180 adjust.........track 270 adjust.........track 90 adjust, all with your GPS. It can even be a portable.

Repeat adjustments above.

Now track 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360 and jot down the corrections. There is no getting into and out of the airplane or drawing any lines on the ground.

Don't make such a quick, simple, and DEAD accurate procedure difficult. Remember that on the ground there is no "wind correction" because all movement is always track.
Click to expand...

Anyone who can do all that in 10 minutes, my hats to them. Still don't have a deviation card or a log entry.[/QUOTE]
 
Bell206 said:
FastEddie's post stated he marked the ramp and swung the compass. You replied: "Once you have a N/S (or any known bearing), the rest is just math." However, basic English implies once you determined a bearing you swung the compass mathmatically. Or did I misread it?
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As I pointed out, you misread it. My comment about "The rest being math" applies to laying out the other compass points to do the swing, not the swinging itself. As I said FE said he used two GPS bearings, one N-S, and one E-W. I was just pointing out that once he had the N-S one, all he needed was a tape measure to be able to generate a perpendicular to it (which is good enough for compass purposes).
Not quite. Unless you have an acceptable reference that states using Google, it can't be used at least for a TC'd aircraft. I've always used a master site compass which didn't require marking anything on the ramp and allowed a lot of flexibility.
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There's nothing that says a GPS can be used for "TC'd" aircraft. However, I disagree with your assertion. Nothing prohibits it. THe FAA tells you to have a certified rose to do the swing but they do not provide any information on how that certification is performed. Using a suitably accurate photogrammetric solution is just as valid (actually more accurate) than using another compass, and about the same as other surveying methods. It would still be a whole lot more accurate than trying to divine a ground track out of an aviation GPS which is only good to 30 feet or so of accuracy.
It's not rocket science to me neither. But I made my fortune actually performing compass swings and signing them off in the book.;)
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Then I'm surprised you're not aware of the FAA procedures for swinging by compass rose. Yes, there are other ways, but they are sort of secondary to this thread.
 
flyingron said:
As I said FE said he used two GPS bearings, one N-S, and one E-W. I was just pointing out that once he had the N-S one, all he needed was a tape measure to be able to generate a perpendicular to it (which is good enough for compass purposes).
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Perhaps I wasn’t clear. Once I had my N/S line I simply drew the E/W line perpendicular to it.
 
flyingron said:
There's nothing that says a GPS can be used for "TC'd" aircraft.
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Sure there is. There’s FAA guidance and OEM instructions (acceptable references) that specifically state you can use a GPS to swing a compass.
flyingron said:
I disagree with your assertion. Nothing prohibits it.
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It doesn’t quite work that way. It’s not a point of it not being “prohibited” but rather the regulatory performance requirements that must be followed with any maintenance (a compass swing) per Part 43. After all, a compass swing is actually a calibration process for a required flight instrument.
flyingron said:
THe FAA tells you to have a certified rose to do the swing but they do not provide any information on how that certification is performed.
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It’s a moot point. Either the rose (calibration pad) is certified or its not and falls to the mechanic to contact the airport to see if it is. A mechanic cannot certify a compass rose. But as an FYI, the information for certifying a compass rose is in the Airport Ops FARs. Unfortunately, the numbers of certified compass roses are declining as fast as rural airports.
flyingron said:
Using a suitably accurate photogrammetric solution is just as valid
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As I implied before, if your “photogrammetric solution” falls under the definition of FAA acceptable data or is acceptable to the Administrator, then it’s a good reference. If not, then you run the risk of violating Part 43 performance rules regardless how accurate it is. It is what it is.
flyingron said:
Then I'm surprised you're not aware of the FAA procedures for swinging by compass rose.
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Aware? Well, considering I linked the current FAA acceptable procedures in post #2, which includes using a compass rose, I’m quite familiar with all of them and have actually used each one. You?
 
It's not in the "airport operations FAR." It's described in an airport design advisory circular, but it's still left to the airport to "certify" the calibration pad.
In fact, it pretty much abdicated the determination of the direction to "competent geophysicist, surveyors or engineers."
 
Question: When you swing a compass using the compass rose on the tarmac, is the compass rose calibrated to true north or magnetic north ? If magnetic north as I suspect, does a gps reference magnetic north ?
 
Doug Reid said:
Question: When you swing a compass using the compass rose on the tarmac, is the compass rose calibrated to true north or magnetic north ? If magnetic north as I suspect, does a gps reference magnetic north ?
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Yes, magnetic north for obvious reasons. And yes, though I suppose there may be settings hidden somewhere, at least on a handheld, to reference something other than magnetic north.
 
kgruber said:
You CAN'T be in flight for a GPS compass card swing. $120 is WAY too much for such a simple and quick procedure. 10 minutes MAX!!
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He mentioned having it calibrated every 30°. Ain't happening in ten minutes. My shop wouldn't do it for that much labor, even if it was just setting north relative to the compass rose.
A buck-twenty for a dozen checks, yeah, seems good.
 
Doug Reid said:
is the compass rose calibrated to true north or magnetic north ?
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Magnetic north. The particulars will be listed on the calibrate certificate similar to this: https://www.arlingtonwa.gov/DocumentCenter/View/267/Compass-Rose-Calibration-Certificate-PDF
Doug Reid said:
does a gps reference magnetic north ?
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Most aviation GPS units I'm familiar with default to true north headings but can be changed to magnetic north headings in the setup page. FYI: The GPS heading mode is also something to check when troubleshooting heading issues between legacy equipment and GPS.
 
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