Isogonic confusion

Dmitri Scheidel

Dmitri Scheidel

Pre-Flight
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Aug 3, 2016
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53
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Northern California
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NorCali.Pilot
Hello!
Right now I'm manually planing my flight plan for tonight from KCCR to KMOD. Route is KCCR - C83 - KTCY - KMOD. And I'm having trouble with the isogonic lines. There is one that crosses the route near KMOD and its 13*3E (I subtract 13.5* from the true course of every leg I got from the plotter). Thing is, when I use SkyVector to double check everything, they show that it's 15* up to 17*E variation for the short legs.

Which do I use? There's only one line near my route, the next one (14*E) is WAY up north and no where near my route. And where did 15*-17*E come from?

Thanks!
 
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My guess is that the variation has changed and the chart is not updated. Looking at the airport data for CCR it shows 17E variation.
 
Don't use SkyVector. It's not reliable for things like that.
BillTIZ said:
My guess is that the variation has changed and the chart is not updated. Looking at the airport data for CCR it shows 17E variation.
Click to expand...

What makes you think the airport data is newer than the chart? It's not. The chart is kept up to date. The 17°E at the airport is from 1980.
 
Don't overfly c83. There is a drop zone between the runways and an ***hole jump plane pilot.

There is another DZ at New Jerusalem, just east of TCY.

These are charted. Meat bombs are totally invisible unless under an open canopy.

Roads and canals make nice landmarks. Just sayin'...
 
Those are charted, but that doesn't necessarily mean that there aren't jumping activities going on elsewhere. Be sure to check your notams and the AFD (er, um, chart supplement).
Flight following helps as long at the jump pilot isn't a big enough a-hole to be throwing people out of the plane without telling ATC like one operation just north of my old home base would do.

Anyhow 1985 is ancient history as far as magnetic variation goes. I'd want something computed in the current century at least. Variation changes regularly.
 
To the OP: just a niggle at best: I find it easier to read when the writer uses an asterisk for the degree sign. 13* 15' 10"E for example.

dmspilot has done it correctly but that takes more time on my keyboard...

Thanks! -Skip
 
MAKG1 said:
Don't overfly c83. There is a drop zone between the runways and an ***hole jump plane pilot.

There is another DZ at New Jerusalem, just east of TCY.

These are charted. Meat bombs are totally invisible unless under an open canopy.

Roads and canals make nice landmarks. Just sayin'...
Click to expand...
I've flown into/over/around C83 many times, never encountered the jumpers (we check to see if a load is up before flight of course).


Skip Miller said:
To the OP: just a niggle at best: I find it easier to read when the writer uses an asterisk for the degree sign. 13* 15' 10"E for example.

dmspilot has done it correctly but that takes more time on my keyboard...

Thanks! -Skip
Click to expand...
I was looking for something on my keyboard that looked closest to a degrees mark, I totally forgot about the *.
 
Dmitri Scheidel said:
But I have the most recent sectional, are those lines not reliable?
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Reliable? How about important? Think about it: As you go into your flight planning mode the only thing you can rely on is the plotter-measured true course, and the accuracy of that line depends on how good you are at drawing lines and reading protractors. But let's assume that your true course line is dead-nuts accurate; the differences in variation that you cite are between 1.5 and 3.5 degrees, and we know that variation is replotted every five years (thanks, MAKG1). The winds are forecast, not observed, and if you use the miserable Winds and Temperatures Aloft Forecast you must interpolate unless you fly directly over the reporting station at the exact pressure altitude given in the FB at the valid time. Deviation is hardly worth talking about. Now let's get down and dirty...how accurately can you follow a course without an autopilot? One degree? Two degrees? Five degrees? See how sloppy the whole thing is?

Pick a variation you like and use it; don't obsess over how accurate it is.
 
dmspilot said:
Don't use SkyVector. It's not reliable for things like that.


What makes you think the airport data is newer than the chart? It's not. The chart is kept up to date. The 17°E at the airport is from 1980.
Click to expand...
And it appears that skyvector flight planning is using airport data on each leg and not chart data.
Maybe the code writer from skyvector can answer that question.
 
MAKG1 said:
Don't overfly c83. There is a drop zone between the runways and an ***hole jump plane pilot.

There is another DZ at New Jerusalem, just east of TCY.

These are charted. Meat bombs are totally invisible unless under an open canopy.

Roads and canals make nice landmarks. Just sayin'...
Click to expand...

The guy who gave me my rental checkout said the jumpers usually stay on the north side of Byron and south would be "safe"?
 
mtuomi said:
The guy who gave me my rental checkout said the jumpers usually stay on the north side of Byron and south would be "safe"?
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South and East are ok for passing by. The DZ is between the runways. If approaching, the jumper dumper often takes off against traffic, sometimes with someone on final.
 
MAKG1 said:
South and East are ok for passing by. The DZ is between the runways. If approaching, the jumper dumper often takes off against traffic, sometimes with someone on final.
Click to expand...

Funny you should mention that, I just drove around the airport to check out how the drive from my place would be like, and I saw him do exactly that. Everyone was taking off on 30, and the jump plane took off from 12. Field looked busy as well, scary practice that...
 
I thought you were in Livermore. LVK is quite a nice airport. Why would you drive out to C83? Unless you live in Disco Bay, it's far from everything.

The jump plane does that all the time. I've had to dodge him several times. I'm not surprised you spotted him. I think the reason is money -- that's a Caravan turboprop. But the L39 guys don't do such stupid stuff. Go check out their hangar next time you drive by. They are quite friendly. It's the Patriots jet team.
 
MAKG1 said:
I thought you were in Livermore. LVK is quite a nice airport. Why would you drive out to C83? Unless you live in Disco Bay, it's far from everything.

The jump plane does that all the time. I've had to dodge him several times. I'm not surprised you spotted him. I think the reason is money -- that's a Caravan turboprop. But the L39 guys don't do such stupid stuff. Go check out their hangar next time you drive by. They are quite friendly. It's the Patriots jet team.
Click to expand...

I'm in Pleasanton, right next to LVK. C83 has cheaper gas and tiedowns, I wanted to check out how bad the drive there is (pretty bad - Vasco Rd goes a long way round, and 580 over Altamont Pass needs serious offroad capabilities from your car, that road is horrible)...
 
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