# magnetic declination

#### deek

##### New Member
I believe that the amount of declination changes in a given area over time, so at some point in time, it was 4degEast and in a few years it could be 5degEast, or something to that effect. Would that mean that runway headings would change over time, and runway 32 could have a heading of 340 or so at some point? Wouldn't this become odd at some point in time.

I bring this up mostly cause I just saw the giant compass on the desert floor by Edwards AFB on google earth, and I was wondering if it was done many years ago, how accurate is it now?

Yeah man, can't wait for the polarity reversal and then it'll be allllll goooooooo.

The rate of change is relatively negligible. Probably less than 3 degrees every 100 years or so. Who knows if the airport will even be there in that time.

Also, remember that runways are NOT numbered to correspond to magnetic orientation, but to magnetic orientation rounded to the nearest 10 degrees. Runway 15 could very well be oriented at 146 magnetic, and you can see that the difference is actually greater than the amount the variation will change in 100 years time. In some cases, the runway number may actually become closer to the actual magnetic orientation over time.

I believe that the amount of declination changes in a given area over time, so at some point in time, it was 4degEast and in a few years it could be 5degEast, or something to that effect. Would that mean that runway headings would change over time, and runway 32 could have a heading of 340 or so at some point? Wouldn't this become odd at some point in time.

I bring this up mostly cause I just saw the giant compass on the desert floor by Edwards AFB on google earth, and I was wondering if it was done many years ago, how accurate is it now?

Yes, runway numbers do change over time, but usually only for those on the cusp (xx4/5 degrees), and not usually due to the slow shift in magnetic change over time.

As stated, the magnetic declination in a given area will change slowly over time, possibly as much as 2-2.5 degrees every hundred years or so. You wont live to see great change

I believe that the amount of declination changes in a given area over time, so at some point in time, it was 4degEast and in a few years it could be 5degEast, or something to that effect. Would that mean that runway headings would change over time, and runway 32 could have a heading of 340 or so at some point? Wouldn't this become odd at some point in time.

I bring this up mostly cause I just saw the giant compass on the desert floor by Edwards AFB on google earth, and I was wondering if it was done many years ago, how accurate is it now?

If you look in the legend of a sectional or vfr terminal chart under Miscellaneous and Isogonic Line you'll see the which value magnetic variation is used. (they should all be 2005 values) the magnetic variation is changed on aviation charts every 5 years.

Nautical charts are not updated regularly as aviation charts are, so in each compass rose on a nautical chart, there are many of them over the whole chart - each compass rose will post the magnetic variation - the year that it was valid for, and then an annual change like .1 degree E annual change or something like that.

so even with something like a .1 degree change it will take 10 years to change the magnetic direction by 1 degree, and around 50 years to make it an issue to change the runway number if they do decide to change the runway number.

Yeah man, can't wait for the polarity reversal and then it'll be allllll goooooooo.

that will mark the end of the world as we know it

The heading of the main runway in ORF went from 047/227 to 048/228. I'm having the hardest dang time staying in the middle now. anic:

I spoke to one of my friends who has a PHd in Geo Physics and brought this up. He says magnetic north moves about 20 feet every year, and that being said the distance at which the pole is moving every year is increasing. This leads scientist to believe that the iron that moves inside the earths core is slowing. The movement of the iorn creates the magnetic feilds which causes the north pole to exsist. Eventualy the iorn will stop flowing, and flow in the oppsite direction which will lead to a magnetic swich, reversing north and south pole. There is no way to predict when this swich will happen, could be tommarow, who knows?

He also brought up the intresting point that we're not sure if the iorn slows and then quickly swiches directions, or slows and then stops for a prolonged period of time, and then swiches directions. If it were to stop, we would have no north pole.... Ouch.

Little tagent here, just food for though.

He also brought up the intresting point that we're not sure if the iorn slows and then quickly swiches directions, or slows and then stops for a prolonged period of time, and then swiches directions. If it were to stop, we would have no north pole.... Ouch.

Little tagent here, just food for though.

Presume you mean "ouch" due to the radiation exposure that would potentially wipe out a large percentage of the life on Earth?

He also brought up the interesting point that we're not sure if the iron slows and then quickly switches directions, or slows and then stops for a prolonged period of time, and then switches directions. If it were to stop, we would have no north pole....

This blog post on the peer reviewed literature says:

1. Reversals usually happen when the magnetic field strength is at its lowest, which probably won't happen for a few thousand more years,
2. Reversals aren't instantaneous and the poles slowly wander to lower latitudes over hundreds of years, and
3. Reversals aren't associated with mass extinctions, so the field apparently doesn't collapse during a reversal.
So, overall, I'm not worried.

If you look in the legend of a sectional or vfr terminal chart under Miscellaneous and Isogonic Line you'll see the which value magnetic variation is used. (they should all be 2005 values) the magnetic variation is changed on aviation charts every 5 years.

I see what you're saying about what it says on the legend, but I thought the change in variation is one of the reasons why sectionals don't last very long. If you take a current sectional and compare it to the same sectional that just expired, the isogonic lines aren't always in the exact same spot.

I had an examiner tell me that runways are evaluated every 10 years, but I don't know how valid that is.

Runways can and do change numbers every once in a [great] while. In the early '90s Indianapolis used to have 4/22's and now they are 5/23's (all the way up to 048.3/228.3 degrees nowadays). I don't know how often they are evaluated, but the numbers don't necessarily change until the airport is good and ready to paint new numbers and change all the signs.

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