quote:

Originally posted by MNSIG:

quote:

Originally posted by trapper189:
Also, since magnetic north moves, how old are your compasses?

I don't think that would matter. The maps/charts change, for the movement, but the needle still points to the magnetic pole. There's a lot more difference using the same compass on the East coast vs West than old vs new maps.

Correct. I misunderstood what sigfreund meant when said “compass card”. I thought a card with correction factors for variation/declination. Rereading what he wrote, clearly "compass card” refers to the spinning part and it has the degree markings on it, like the half-sphere on my sailboat’s compass, not a needle pointing to degree marks on an azimuth ring.

True story:
Dad had a boat and one day noticed the electronic compass was off from the regular compass. We did the calibration procedure for the electronic compass which involved running the boat in circles and figure eights. Didn’t work. Call the man. Man spends 30 minutes, then determines there was a tool box next to the sensor for the electronic compass. My Dad had rearranged the stuff in the boat before the compass suddenly stopped working.

I had to confirm it before my original post, but there are two ways compasses point to the magnetic pole. One is a freely-rotating needle, and that’s used on compasses that are commonly used for map reading. The second type uses a “card” that is magnetized in some way without a separate needle. The card is marked in degrees and directions and the entire card rotates to indicate direction. Cards are used in military lensatic compasses and in the two types I checked myself. Like many terms, “card” can mean different things in different usages.

The issue I raised about checking to ensure that the compass actually points to magnetic north would less likely pertain to needle indicators.

My late father in law was a Air Traffic Controller . He said that the runways all had a compass rose painted on them to let pilots give a quick check of their eqpt . This was quite a few years ago . Is this still done ?

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Originally posted by Redleg06:
I taught Map and Land Navigation at the Field Artillery School, at Ft. Sill, Oklahoma (1971 -1973).

I will never forget the abundance of rattlesnakes there.

I haven't been to Sill since early 2013 but I'm sure Lawton is still a lovely town.

I used lensatic compasses from my Boy Scout time through college, then moved to the Army's M2 compass when I was commissioned into the Field Artillery; it became my preferred compass. It was great that one could set the declination on the M2 to adjust for magnetic-to-grid north. As a battery XO, the last thing I did after the battery was laid and before a round went downrange was to use the M2 compass to get a final check the azimuth of lay behind each howitzer (a ballpark figure given all the metal).

I don't know if this was widespread across the country, but there is a road in town called "Meridian Street". There are 3 (surviving) old stone markers that were placed along the meridian for surveyors to calibrate their instruments. The Massachusetts legislature had these placed in 15 locations across the state in 1870. I have a list of all of these if someone were really interested.

FAGS (field artillery guys)

This had me laughing.

As a former "Artillery Surveyor", we always declinated our compasses before we did ANY survey work. As you can imagine, a 155mm howitzer has a range of about 22-24 miles. if your compass is off by one mil (0.057deg), the resultant ordinance could be off by quite a bit.

quote:

Originally posted by selogic:

My late father in law was a Air Traffic Controller . He said that the runways all had a compass rose painted on them to let pilots give a quick check of their eqpt . This was quite a few years ago . Is this still done ?

Not quite correct. It is not true that "the runways all had a compass rose painted on them."

There are compass roses at many airports for this purpose, but certainly NOT at all airports, and I have never seen one on a runway. They are usually on a ramp area.

FAA Advisory Circular AC 43-215, titled "Standardized Procedures for Performing Aircraft Magnetic Compass Calibration," can be found here:

https://www.faa.gov/documentLi...C_43-215_FAA_Web.pdf

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Originally posted by V-Tail:
Not quite correct. It is not true that "the runways all had a compass rose painted on them."

There are compass roses at many airports for this purpose, but certainly NOT at all airports, and I have never seen one on a runway. They are usually on a ramp area.

V-Tail is correct, no surprise there. At Montgomery Field (KMYF) in San Diego, CA the compass rose that was painted on the ramp just outside of the ATC Tower was taken out when the Fire Department built their facility several years ago.

If its located someplace else on the airport, I haven't seen it.

Next time I'm near one of the avionic shops, I will ask how they currently update the calibration card for the wet compass in an aircraft. I expect they compare the aircraft wet compass with some hyper-calibrated devise. Back in 1984 during my primary flight training, one of my instructors had me taxi out to the Compass Rose at MYF to verify the Compass Card was accurate.


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