Northern runway identifiers

[Donald]

So I see that the runway ID's for a bunch of northern airports (CYHY, CYZF, CYSM, CYFS, etc) have all changed recently, but the magnetic headings are the same as before. Is this a Jepp error, or am I missing something?

[Donald]

No Navcan guys lurking here with the answer?

[SierraPoppa]

It's likely the compass variation has changed enough to require the runways be re-numbered.

Anyone remember when Edmonton International had 11/29 and 01/19?

[Woxof38]

I think it was changed a couple of supplements ago.

[wannabepilot]

Magnetic drift is .2 degrees per year (I think). If a runway was built with a departure heading of exactly 100 degrees, it would be named Runway 10; after 25 years it would have a departure heading of 105 degrees, necessitating a renaming to Runway 11. You wouldn't notice a change in runway heading on your compass unless you had a compass accurate enough to pick up the .2 degree change from the previous year.

[SierraPoppa]

Magnetic drift is .2 degrees per year (I think). If a runway was built with a departure heading of exactly 100 degrees, it would be named Runway 10; after 25 years it would have a departure heading of 105 degrees, necessitating a renaming to Runway 11. You wouldn't notice a change in runway heading on your compass unless you had a compass accurate enough to pick up the .2 degree change from the previous year.

There isn't a fixed rate of change, it varies with location relative to magnetic north.

http://www.navcanada.ca/ContentDefiniti ... urrent.pdf

If you look on the aerodrome charts for all airports you can see the magnetic variation along with the annual rate of change for each airport. Some northern airports the rate of change is large (Alert 74.6'E per year) others very little (Rankin Inlet 1.7'W per year).

The further south you go the more consistent the rate of change (Edmonton International 16.0'W per year and Lloydminster 16.9'W per year) and it gets less the further south you go (Lethbridge 13.0'W per year Medicine Hat 13.3'W per year).

[W0XOF]

Magnetic drift is .2 degrees per year (I think). If a runway was built with a departure heading of exactly 100 degrees, it would be named Runway 10; after 25 years it would have a departure heading of 105 degrees, necessitating a renaming to Runway 11. You wouldn't notice a change in runway heading on your compass unless you had a compass accurate enough to pick up the .2 degree change from the previous year.

There isn't a fixed rate of change, it varies with location relative to magnetic north.

http://www.navcanada.ca/ContentDefiniti ... urrent.pdf

If you look on the aerodrome charts for all airports you can see the magnetic variation along with the annual rate of change for each airport. Some northern airports the rate of change is large (Alert 74.6'E per year) others very little (Rankin Inlet 1.7'W per year).

The further south you go the more consistent the rate of change (Edmonton International 16.0'W per year and Lloydminster 16.9'W per year) and it gets less the further south you go (Lethbridge 13.0'W per year Medicine Hat 13.3'W per year).

Although I'm not looking at a chart, I'm not sure the "rates of change" you have listed above are just that. Those look like the magnetic variation. If those are annual rates of change they'd be painting new numbers on the runways every 10 months in YQL and YXH.

[W0XOF]

Oh yeah, just to add further, the variation numbers don't become more consistant in the south. The zero declination line runs somewhere through Hudsons Bay, North-South. The further East from that line you go, the variation gets bigger, just as the further West from that line you go, the variation gets bigger. West of the zero declination line the declination variation shows E and East of the declination line the variation shows W (CYKA 17 E, CYYZ 10 W for instance).

http://geology.isu.edu/geostac/Field_Ex ... s/mdec.jpg

[wannabepilot]

The numbers SierraPoppa quoted are magnetic variation, which is the amount of degreees that separates true north from magnetic north for a given location. I was talking about the amount that magnetic north moves each year relative to true north, and the change that causes in a runway's numbering due to its new orientation relative to magnetic north.

[photofly]

I'm not sure the "rates of change" you have listed above are just that. Those look like the magnetic variation.

They only "look like" the magnetic variation because you didn't notice the figures in SierraPoppa's post were in minutes of arc per year and not in degrees.

[W0XOF]

Thanks photofly. That makes sense.

[combine]

Magnetic variation change occurs on a regular basis, but publication changes renaming runways only happens after the runways are repainted to reflect the new heading. For some airport authoritys, this came take up to two years or more.

[Beefitarian]

Some of you guys might not want to fly around Alert, you're going to get quite lost calculating your heading using "74.6'E" as variation.

[Dagwood]

Some of you guys might not want to fly around Alert, you're going to get quite lost calculating your heading using "74.6'E" as variation.

If they think that is correct then they can go ahead and use it

[Donald]

That all makes sense, but how do you explain the fact there is zero change to the published mag heading for the runways or the mag variation for the airports??

[Beefitarian]

If you go back and look at the post with the "rates of change" they are minutes per year, a degree is divided into sixty minutes. It takes a while for the variation lines to change but if you compare old charts and flight sups you'll see they do change over time. Find one that's twenty or thirty years old and the numbers published then will be different from the ones that are current.

[Joe Blow Schmo]

That all makes sense, but how do you explain the fact there is zero change to the published mag heading for the runways or the mag variation for the airports??

The change probably happened a while ago but the runways are only just being renumbered now. So the mag heading of the runway probably changed in a previous publication and the number is changing now. Is the new runway number correct for the mag heading? (ie. if the RWY has switched from 10 to 11 it should be 105 degrees).

[Donald]

Is the new runway number correct for the mag heading? (ie. if the RWY has switched from 10 to 11 it should be 105 degrees).

This is what I was getting at, the mag heading in YZF for example is 334/154, now to be named 34/16. It's the same at YSM, YHY, YFS. Jepp error or something else?

[Posthumane]

Slightly off topic, but there is a significant difference between how the isognic lines (equal magnetic declination) are presented on modern VNCs and older maps. I have some nav charts from WW2 for canada, and the isognic lines are very squiggly and seem to run in very irregular patterns, as compared with the almost straight lines on current VNCs. Were they more precise about measuring magnetic declination in various places in those days to take into account local terrain influence? I assume the isognic lines on modern maps are based on a model and not actually measured on the ground.

Also, magnetic declination in southern alberta is shown to be about 15-17 degrees on current VNCs. On the older ones it was about 20-22 degrees, so it has moved a fair bit. However, US sectional charts which extend into canada show different magnetic declination. What's up with that?

[Donald]

Spoke to the YZF tower, and the mystery is solved.

It's a publication issue, the magnetic headings and compass declination have indeed changed, the new info just didn't make it into the latest amendments.

Thanks for the informative replies, even though no one was able to answer the original question.