Fly Victor airways with RNAV?
- Thread starter FORANE
- Start date
I so rarely get assigned the airways, but I do not believe that there is anything inherently wrong about using my IFR-cert GPS to maintain track on the airway. The applicable VOR is tuned and radial selected for cross-check, of course.
roncachamp
Final Approach
Why shouldn't it be done?
John Collins
En-Route
Have you got something to share with us and the writers of AC 90-108?
Brad Z
Final Approach
Are you confusing RNAV with using an uncertified handheld GPS? There's nothing that prohibits the former.
All the time. Here in the NE, you'll almost always get victor airways as a matter of course. Down south, if I ask for direct, I usually get it, unless RADAR is out. Then the 480 shines. Select the airway and get on it. The thing even shows you all the intersections on the airway with your ETA to each one...Makes position reports a dream.
azure
Final Approach
Yup! But so far, I've only gotten a victor airway once. Most often direct to a fix, and once in a while "cleared as filed"... i.e. direct.
HPNPilot1200
En-Route
Completely, 100% legal. Plus, if you have WAAS, you don't even need operational navaids to fly the airway.
Why should we not do it?
Why should we not do it?
What is a Victor Airway.
Get with it man.... This it the 21 century, we go <direct> using GPS.
Get with it man.... This it the 21 century, we go <direct> using GPS.
One good reason to fly airways might be collision avoidance, since there will apparently be no one else there!
On the other hand, if many people did it using GPS, I suppose that might increase collision potential, due to more aircraft being precisly centered on the airway.
On the other hand, if many people did it using GPS, I suppose that might increase collision potential, due to more aircraft being precisly centered on the airway.
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Everskyward
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Everskyward
Isn't that what happened in Brazil? The two airplanes were on the same airway but mistakenly at the same altitude.
Marauder
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Marauder
I'm betting this is a trick question
Wasn't there something discussed years ago about the difference between a VOR radial making up an airway and the great circle nav provided by GPS for the same route?
Wasn't there something discussed years ago about the difference between a VOR radial making up an airway and the great circle nav provided by GPS for the same route?
John Collins
En-Route
I'm betting this is a trick question
Wasn't there something discussed years ago about the difference between a VOR radial making up an airway and the great circle nav provided by GPS for the same route?
A VOR radial is a great circle route.
EdFred
Taxi to Parking
If I am flying from Harrisburg VOR to Myton VOR they are pretty much at the same latitude, so the radial on a chart between the two is 270. But the great circle route has an initial heading of 290ish.
Yes, I know - outside of service volumes and all that, but the point remains.
roncachamp
Final Approach
Yes. The mistake was the controller's, they were both level at their assigned altitudes.
roncachamp
Final Approach
I'm betting this is a trick question
Wasn't there something discussed years ago about the difference between a VOR radial making up an airway and the great circle nav provided by GPS for the same route?
Seems unlikely, as VOR radials form great circles.
ja_user
Pattern Altitude
no doubt if they had been tracking with a VOR, they would have been off enough to miss each other
roncachamp
Final Approach
No, the radial on a chart between the two is 291.
TMetzinger
Final Approach
The difference between the track flown when using the VOR as your guidance and the track flown when using the GPS as your guidance is negligible, and well within the "width" of the airway.
That said, it assumes that you are putting in the appropriate fixes into your GPS route - the same intersections between your navaids.
That said, it assumes that you are putting in the appropriate fixes into your GPS route - the same intersections between your navaids.
Aww. I was not aware of AC 90-108. After all the hammering into me during the instrument ticket years back that I could not use the gps on airways, I didn't think it was allowed.
I have a non-waas Garmin 430. Would like direct and request it but often put on airways. Just wish the 430 allowed airway entry in flight plan and not require all those pesky intersections, twisting and pecking, nonsense.
Maybe Avidyne will get its act together with the IFD-440.
I learned something already, thanks guys.
I have a non-waas Garmin 430. Would like direct and request it but often put on airways. Just wish the 430 allowed airway entry in flight plan and not require all those pesky intersections, twisting and pecking, nonsense.
Maybe Avidyne will get its act together with the IFD-440.
I learned something already, thanks guys.
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EdFred
Taxi to Parking
I draw straight lines on a chart, not arcs as I don't have a giant compass. an east west line on the chart is 270ish true, and HAR doesn't have 20 degrees of variation.
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John Collins
En-Route
Assuming the signal could be received over the distance, the circle route is the shortest route in space. Not considering relativistic effects of gravity, the VOR transmission will follow a straight line in space. The shortest distance between the two locations would require the departure from HAR on approximately the radial that aligns with a true course of 281 degrees. This is about 11 degrees north of true west. Arriving at MTU, the course would be approximately 259 degrees true, about 11 degrees south of west. The arc is to the north on a flat surface chart, but is the shortest distance on the surface of a sphere (stretch a rubber band between the two points on a globe to simulate it). To convert those to VOR magnetic radials, one would have to adjust the HAR radial by the 1985 variation of 10 west and the MTU radial by the 1980 variation of 14 East. So to go direct between the two VOR's, assuming you could, you would track outbound on the HAR 292 radial and the 065 radial inbound to MTU.
roncachamp
Final Approach
Then you're not drawing radials.
roncachamp
Final Approach
Magnetic variation in the HAR area is about 11W but the VOR is set to 10W, so it's the 291 radial.
John Collins
En-Route
I draw straight lines on a chart, not arcs as I don't have a giant compass. an east west line on the chart is 270ish true, and HAR doesn't have 20 degrees of variation.
If you lay a rubber band down on the globe between the points to form the shortest distance, it will lie almost on Des Moines, IA. Your straight line falls lower onto Mo and never even touches IA. At Chicago, you are almost 100 NM to the south whereas the rubber band is approximately 35 NM south. Radio waves just are only familiar with following a straight line thru space, curves not so much. However, a straight line in space appears as a curve on a flat chart that is constructed by a projection of the varying latitudes onto the sphere. The opposite is true, the straight line on the chart with varying latitude is always a curve in space.
EdFred
Taxi to Parking
Yes, but I don't have a giant globe at my house to run a string across. I have charts with lines of lat/longitude on a flat surface. Though I do realize that plugging in HAR -D-> MTU on my GPS does give me the great circle heading. When I fly direct HAR from west Michigan, my DTK changes over the course of the trip even though my TRK is indicating the same vector. It just won't agree with what I planned at home.
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EdFred
Taxi to Parking
I'm pretty sure that any vector from a VOR is on a radial.
roncachamp
Final Approach
How do you define "vector" for this purpose?
EdFred
Taxi to Parking
Draw a line segment on chart originating from HAR VOR to MTU VOR using a straight edge, and the pencil moving at 2inches/second. (A vector needs a direction and velocity, you know.) Look to see where line crosses the circle around the VOR. Yep, looks like it's on a radial.
roncachamp
Final Approach
Actually a vector requires direction and magnitude. Velocity is itself a vector quantity, specified by speed and direction.
If you extend that 270° "vector", what we call a "radial", west to W110° 7.62' longitude, you'll find yourself about 580 miles south of MTU.
EdFred
Taxi to Parking
I didn't say it was the correct radial to get to MTU if drawn on a chart vs what's actually flown. I said it was on a radial.
roncachamp
Final Approach
No, that's not what you said, this is what you said:
The radial between them, extended without regard to service volume, is not the 270° radial, it's the 291° radial.
EdFred
Taxi to Parking
The radial on the CHART shows one thing. The radial in real world however is another, and it's only an initial heading. I have to come off that radial at some point, because the radial from MTU would not be 111 - it's 065. You can't keep flying the 291 heading to get to MTU.
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John Collins
En-Route
You could if the signal went that far. The magnetic track would vary along the flight to maintain the centerline of the radial, but the radial setting on the VOR would remain the same if you wanted to fly the shortest path.
EdFred
Taxi to Parking
And if I went really really high. And I should have said heading. Either way, what I plan out at home without having a giant globe is not going to coincide with what I need to fly in the real world.
roncachamp
Final Approach
Yes, you were correct when you said "great circle route has an initial heading of 290ish", the initial heading will always match the radial at the source. That's pretty much what is meant by initial heading. You were wrong when you said the radial between HAR and MTU is the 270° radial, if it extended that far.
EdFred
Taxi to Parking
As drawn on a chart, on a flat surface it would be 270ish, which is what I originally said. On the chart it would show that, because I do not have a globe large enough to wrap sectionals (or other maps) around. They would be on a flat surface, so the straight line drawn on the chart (as shown in the picture above) does show 270ish - albeit erroneously.
Just like the wall map I have at work. If I draw a line from 30W to 30E at a latitude of 45 degrees starting on the agonic, it would show me as being on the 270 or 90 radial from that originating point.
Of course, I could fly 270ish true and get there. It's just not the shortest distance, but my heading wouldn't ever change.
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