Reading GFA during test

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rotorspeed
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Reading GFA during test

Post by rotorspeed »

I've had trouble reading a GFA during a practice exam if I don't know the area. Fx if it's asks what is weather over Edmonton trying to decider where it is unless I use my phone to check the provincial borders. AM I the only one
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FL_CH
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Re: Reading GFA during test

Post by FL_CH »

On the exam they will normally map the airports right on the GFA. It's likely that your practice exam doesn't do it.
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CpnCrunch
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Re: Reading GFA during test

Post by CpnCrunch »

Don't worry, it won't be an issue. The actual exam will always have a GFA from another province, so nobody knows the airports. It will never ask you for information that isn't available.
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rotorspeed
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Re: Reading GFA during test

Post by rotorspeed »

Thanks guys that relieves me
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rotorspeed
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Re: Reading GFA during test

Post by rotorspeed »

Could you guys answer a question about lf radicals on VNC they don't correspond to magnetic headings correctly the map says under definitions quarter mAh variation.
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455tt
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Re: Reading GFA during test

Post by 455tt »

Are you located within the Northern Domestic Airspace, where all radials, tracks and bearings are in degrees True instead of Magnetic?

If this does not help, can you re-word or elaborate your question?
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rotorspeed
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Re: Reading GFA during test

Post by rotorspeed »

Could you guys answer a question about LF NDB radials on VNC. they don't correspond to magnetic headings correctly. The map says under definitions " quarter mile variation"
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455tt
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Re: Reading GFA during test

Post by 455tt »

OK I have a better idea now what you are asking about.

So let us first consider a track vs. a heading.

A track is what you measure over the surface of the earth. It can be either true or magnetic depending on whether you measure from true north or magnetic north.

Then we have a heading, which is where the longitudinal axis of your aircraft is pointing, either true or magnetic.

Now when you measure a track on a VNC chart, you measure with your protractor from the midpoint of track, so as to average out the error caused by the convergence of meridians. You must also factor in the magnetic variation at the point of measurement of track as determined from an isogonic line of magnetic variation.

When you see a VOR radial on a chart, it is a magnetic track, and you will see a different number will appear inbound from the station as compared to outbound from the connecting station. This difference is caused by the convergence of meridians. It is also caused by the difference in magnetic variation at each end of the radial. Same for an NDB track.

A radial to or from a VOR can be named as a VHF airway.

A track to or from an NDB can be named as an LF airway.

Not sure if this is making any sense but does this help?

TT
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455tt
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Re: Reading GFA during test

Post by 455tt »

I should also mention that airway tracks (VOR and NDB) as presented on charts within the Southern Domestic Airspace are displayed in terms of degrees Magnetic, not degrees true and this may account for any difference you may have if you measured the track in degrees True.
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rotorspeed
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Re: Reading GFA during test

Post by rotorspeed »

So if I use a published vor radial against the map with plotter such as around Vancouver and then subtract the bariation6 17E . Then it works out right. When I use one from to published lines running from NDB and then account for the 17e variation it's off by up to 4 degrees. I tried it a few times but get the same result. Also the reciprocal heading is more than 180 degree off. I know I have to account for the change of one degree in the variation but it's more than that. Again this is only for the NDB lines not vor. Yes a I'm doing something wrong. I appreciate the help by the wau
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AuxBatOn
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Re: Reading GFA during test

Post by AuxBatOn »

NDB bearings and VOR radials aren't quite the magnetic tracks. VORs and NDBs need to be rotated to line up with magnetic North every so often. It doesn't always happen regularly but it should be close enough not to be disorientating when you are trying to track a VOR or NDB. In the SDA, you should not reference True Tracks/headings but rather magnetic tracks/headings.
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455tt
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Re: Reading GFA during test

Post by 455tt »

Interesting.

We can also throw into the mix airway tolerances and parameters for IFR, which include that the accuracy of course alignment for a published VOR radial can differ by up to +/- 3 degrees from that published, and published LF airways are flight checked to an accuracy of only +/- 10 degrees. As well, a VHF airway has a width of 4 NM either side of centre, widening at a 4.5 degree splay. And an LF airway has a width of 4.34 NM either side of centre, widening at a 5.0 degree splay. Not to mention aircraft tolerances for VOR based on an airborne check can be up to +/- 6 degrees and still be considered usable for IFR. Yet even with these multiple inaccuracies and tolerances we can still rely on the system for IFR navigation. And on LO charts the navaid symbols themselves can be offset for presentation purposes as well, I am not sure if this offset can also be applied to VFR charts.
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rotorspeed
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Re: Reading GFA during test

Post by rotorspeed »

I'll try tomorrow to post a specific airway from the vnc. But I understand what you're saying
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