Compass Correction/Deviation Card

J

JOhnH

Touchdown! Greaser!
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I just noticed that my Compass card is missing. I know it was there recently, but not actually sure when the last time I paid attention to it was.

Should the numbers be in the log book? I looked and didn't see it, but there are over 50 years of entries, and many of them are hand written.

If I can't find the old numbers, can I fill out a new card myself or do I need my A&P to do it?

If I can do it myself, is there an accepted procedure that doesn't involve a Compass Rose?
 
JOhnH said:
If I can do it myself, is there an accepted procedure that doesn't involve a Compass Rose?
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Credit goes to Barry Schiff for this procedure: In lieu of a compass rose, look up the exact magnetic heading of the runway and align the aircraft with it, then set the gyroscopic heading indicator to that heading. Turn to cardinal headings in 30° increments and note the deviation with the engine running at a reasonable flight RPM. You can check to make sure the gyro hasn't drifted at the 180° and 360° points.

Whether a pilot can fill out a compass card legally, I can't tell you, and have not found a convincing answer one way or the other.
 
The fastest, most accurate method is to use your GPS on the ground. A mechanic must sign it off.

"""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."""

http://www.airpathcompass.com/J30/index.php
 
dmspilot said:
Whether a pilot can fill out a compass card legally, I can't tell you, and have not found a convincing answer one way or the other.
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The fact that it’s not in the list of preventative maintenance items that can be done without A&P supervision/sign off seems pretty convincing to me.
 
dmspilot said:
Credit goes to Barry Schiff for this procedure: In lieu of a compass rose, look up the exact magnetic heading of the runway and align the aircraft with it, then set the gyroscopic heading indicator to that heading. Turn to cardinal headings in 30° increments and note the deviation with the engine running at a reasonable flight RPM. You can check to make sure the gyro hasn't drifted at the 180° and 360° points.

Whether a pilot can fill out a compass card legally, I can't tell you, and have not found a convincing answer one way or the other.
Click to expand...

You can do that but I'd bet it is not anywhere near equivalent to being on a real compass rose that has actually been surveyed and marked in the last 24 months.
 
JOhnH said:
If I can do it myself, is there an accepted procedure that doesn't involve a Compass Rose?
Click to expand...
A mechanic needs to sign it off. As to alternate procedure, yes by using a Master Sight compass which can be rented for a reasonable rate. Most airport compass roses are out of calibration as the earth's mag field has been moving faster than normal. A quick call to the tower will confirm if an airport's rose is calibrated. Keep in mind the mag compass is technically a navigation device and you need to use calibrated test equipment in order to stay within the requirements of Part 43.13. Personally, I've only used a master compass over the past 25 years since it can be used anywhere.
 
There are several places that you can down load a blank card, fill it out put it in the holder.
It is a required placard it must be in place to be airworthy, but the FAA doesn't give a hoot if it is acrurate.
 
MauleSkinner said:
The fact that it’s not in the list of preventative maintenance items that can be done without A&P supervision/sign off seems pretty convincing to me.
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There nothing on the preventative maintenance list that says you can make a copy of an ignition key either, but I am pretty sure I don’t need a mechanic for that.
 
Doug Reid said:
Make it legible....put it in view of the pilot.

The only time your compass is presenting accurate information is in level, unaccelerated or decelerated flight.

Tom is correct in his response...it needs to be in place...accuracy is another matter. The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.
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What (on the GPS) do you set it to after takeoff? GPS can give you ground track but not heading.
 
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jsstevens said:
What (on the GPS) do you set it to? GPS can give you ground track but not heading.
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If you are taxiing, how much is your heading going to vary from course? ;)

(assume dry conditions, on ice things can change)
 
EdFred said:
If you are taxiing, how much is your heading going to vary from course? ;)
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Taxiing is fair but the post I responded to said he used the compass only to set the DG before takeoff and thereafter set it to the GPS. He neglected to mention he was only taxiing around. o_O
 
Clip4 said:
There nothing on the preventative maintenance list that says you can make a copy of an ignition key either, but I am pretty sure I don’t need a mechanic for that.
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Is that considered aircraft maintenance?
 
kgruber said:
Taxiing on the ground, track and heading are the same.
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Again the post I responded to said he set the DG using the compass just before takeoff and then used the GPS for the rest. It certainly SOUNDS like he uses the GPS in flight.
 
Doug Reid said:
Make it legible....put it in view of the pilot.

The only time your compass is presenting accurate information is in level, unaccelerated or decelerated flight.

Tom is correct in his response...it needs to be in place...accuracy is another matter. The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.
Click to expand...

How does that work when you have a 25 degree crosswind correction? Might want to rethink that strategy. Course and heading arent the same thing.
 
EdFred said:
How does that work when you have a 25 degree crosswind correction? Might want to rethink that strategy. Course and heading arent the same thing.
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My point exactly.
 
Tom-D said:
To Duplicate the card, NO! put one in place and go fly.
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That's the point. He's not duplicating the card as he doesn't have the original heading compensation values. And considering those values can be up to +/- 10 degrees off, what numbers would you recommend he put on his card?

Why not just swing the compass and put the correct values on the card?
 
Doug Reid said:
Make it legible....put it in view of the pilot.

The only time your compass is presenting accurate information is in level, unaccelerated or decelerated flight.

Tom is correct in his response...it needs to be in place...accuracy is another matter. The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.
Click to expand...

kgruber said:
He said that he set his DG to the GPS on the ground and then used the DG to record the compass calibration. The DG would not precess much in the 3 minutes it would take to make 12 turns/readings.
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I think you're reading something different than what we are reading. The implication of his post is that after takeoff he sets his DG to the GPS.
 
kgruber said:
No. The implication is that he records his compass correction card off the DG. I doubt he is an idiot.
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Maybe not but this is what his post says:” The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS.” I’m not sure why he’d say “before takeoff” if he’s only swinging the compass.
 
EdFred said:
The implication of his post is that after takeoff he sets his DG to the GPS.
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kgruber said:
No. The implication is that he records his compass correction card off the DG. I doubt he is an idiot.
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It's not an implication. He literally said exactly that he sets his DG to his GPS after takeoff.

"The only time I really look at a compass is when I set my DG before takeoff...from that point on I set my DG to the GPS."

This thread turned into a real WTF even for POA.
 
jsstevens said:
What (on the GPS) do you set it to? GPS can give you ground track but not heading.
Click to expand...

At Copperhill Airport I made a GPS waypoint at the windsock. I then paced off a distance and marked 2 more waypoints that were directly south of that waypoint. Then painted a line between them, to establish a N/S reference, then painted a perpendicular E/W line. Easy to then get the 30° increments.

Worked well enough on my Sky Arrow. I assume being Experimental there was no issue with rolling my own. I don’t remember the plane being delivered with a compass correction card.
 
kgruber said:
No. The implication is that he records his compass correction card off the DG. I doubt he is an idiot.
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So he sets his Compass Card after take off? Re-read what he said.
 
"Why, that card was in there when I bought the airplane..." :cheerswine:

The compass correction card is an anachronism, a throwback to the days when we drew pencil lines on paper maps and a 3° error would put you into the next county at the end of a 4 hour cross-country. Between VOR, GPS, and the lot of it, NOBODY I know uses that piece of paper for anything but required equipment for a checkride. Nobody gives a damn if it is wildly inaccurate.

HOWEVER, there was a compass manufacturer named Tate that once put out a batch of compasses with the directions reversed ... west was east, north was south and so on. Which is where we get the saying, "He who has a Tate's is lost."

Jim
 
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Doug Reid said:
On the ground is correct. I set the DG to the compass on the taxiway in front of my hangar when I start up, and verify with the gps as I taxi to the active runway. I don’t have a vertical card compass...posted in a hurry...but have to admit I enjoyed the attention. Kgruber wins the door prize today !
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How do you set it in flight? This combined with your other post implies that you don't ever reset it after takeoff. And the comment about not having a vertical card compass is a non sequitur.

You wrote something that made no sense and kgruber was more successful at mind reading than the rest of us. No prizes will be given.
 
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Clip4 said:
You are duplicating a part. The key comes with the ignition or the ignition / door lock set. If you can’t replace a placard, how can you replace a key.
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I guess the key needs A&P supervision/signature, then.
 
Bell206 said:
That's the point. He's not duplicating the card as he doesn't have the original heading compensation values. And considering those values can be up to +/- 10 degrees off, what numbers would you recommend he put on his card?

anything he wants, when was the last time you saw a ramp checker say the card was wrong?

Why not just swing the compass and put the correct values on the card?
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Because he is not allowed to do that.

That is calibrating an aircraft magnetic compass.
Actually if you nit pick it, that requires a certified Instrument repair shop.
Now tell me if adjusting the composting magnets is an alteration of the instrument?
65.81 General privileges and limitations.
(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).
Are you repairing a compass that was wrong, by adjusting it?

If we are allowed to adjust a compensating magnet assembly, why aren't we allowed to service the fluid level?
 
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Tom-D said:
That is calibrating an aircraft magnetic compass. Actually if you nit pick it, that requires a certified Instrument repair shop.
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Ha. Are we talking about the FARs or the TARs? Funny, between the FAA guidance I mentioned above and other guidance like AC-43.13-1B all state a mechanic can swing a compass:
"Certificated airframe mechanics and certificated repair stations (CRS) with the appropriate ratings are authorized to perform a compass swing, which includes adjustment of compass compensators."

But you are right on the repairs:
"Repairs or alterations to a compass may only be made by a CRS holding an appropriate instrument or limited instrument rating."
Tom-D said:
Are you repairing a compass that was wrong, by adjusting it?
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No.
Tom-D said:
why aren't we allowed to service the fluid level?
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I'm from the side an A&P can service a mag compass as it's not a repair or alteration. Kind of like servicing an engine with oil. Can a pilot do that? And does it require a logbook entry like hydraulic fluid servicing?


 
For about $80, my local Av shop used a calibrated magnetometer aimed at the spinner centerline of my aircraft with an optical sight as the plane was turned about the compass rose. The magnetometer verified exactly where the plane was pointing and the different in shipboard compass indication was noted.

For the life of me, I cannot see how someone could calibrate a compass from a compass rose. It's very difficult to know the 1-4º of variation that needs to be documented on the compass card from a painted marking.

I like an accurate compass card, just incase I ever urgently needed to fly by compass. Just one of my minimums, I'm sure others don't care.

-David
 
Bell206 said:
I'm from the side an A&P can service a mag compass as it's not a repair or alteration. Kind of like servicing an engine with oil. Can a pilot do that? And does it require a logbook entry like hydraulic fluid servicing?
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I'd like to be able to do the servicing of a compass fluid, but unfortunately that requires opening the instrument.
You are correct, adjusting any instrument that does not require opening the instrument to do so is simply an adjustment, not a repair. but unfortunately the FAA feels that removing the top plug, and filling the fluid is a repair of an instrument.
 
This post makes my head hurt.

So glad I don't have to deal with this archaic nonsense in the experimental world.
 
Lndwarrior said:
This post makes my head hurt.

So glad I don't have to deal with this archaic nonsense in the experimental world.
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Have you forgotten there are members here that might have learned some thing?
I'm sorry your head hearts, But when examined, I'd be scared if I had a head like your's and it didn't hurt. :)
 
NordicDave said:
I like an accurate compass card, just incase I ever urgently needed to fly by compass. Just one of my minimums, I'm sure others don't care.
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The way a compass bounces around, and the close spacing of the markings, plus turning and acceleration/deceleration errors, makes exact, exact precision illusory.

I think I recall that a 1° error means one mile off course over a 60 mile distance. I found this comforting when using a compass and dead reckoning to navigate long over-water legs in the Caribbean - I could be several degrees off and still have confidence that the next island in the chain would still eventually slide into view. Not to mention the inherent inaccuracy of winds aloft forecasts.

Don’t get me wrong, I’d like my compass to be as accurate as possible. But a few degrees error one way or another is unlikely to be much of an operational factor in real life flying.
 
NordicDave said:
For about $80, my local Av shop used a calibrated magnetometer aimed at the spinner centerline of my aircraft with an optical sight as the plane was turned about the compass rose. The magnetometer verified exactly where the plane was pointing and the different in shipboard compass indication was noted.

For the life of me, I cannot see how someone could calibrate a compass from a compass rose. It's very difficult to know the 1-4º of variation that needs to be documented on the compass card from a painted marking.

I like an accurate compass card, just incase I ever urgently needed to fly by compass. Just one of my minimums, I'm sure others don't care.

-David
Click to expand...

Each mark being 5 degrees, its easy enough to get under 4 via eyeballs. Drive around the compass rose again and its easy to see that it is repeatable. It can be a lot easier with a tech outside helping the driver get lined up, (second tech is SOP where I work)

Did the same after calibrating a G5 HSI, compass rose works well.

Without someone actually coming out and testing an area for magnetic disturbances on schedule, I don't see how any tool could be used to calibrate a compass.


upload_2019-5-2_6-47-8.png
 
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FastEddieB said:
The way a compass bounces around, and the close spacing of the markings, plus turning and acceleration/deceleration errors, makes exact, exact precision illusory.

I think I recall that a 1° error means one mile off course over a 60 mile distance. I found this comforting when using a compass and dead reckoning to navigate long over-water legs in the Caribbean - I could be several degrees off and still have confidence that the next island in the chain would still eventually slide into view. Not to mention the inherent inaccuracy of winds aloft forecasts.

Don’t get me wrong, I’d like my compass to be as accurate as possible. But a few degrees error one way or another is unlikely to be much of an operational factor in real life flying.
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I’ve been fairly impressed over the years with compass accuracy...a couple of long DR legs have gotten me within 3-4 miles of my destination, so overall less than two degrees of error.
 
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