Mick Galvin
Filing Flight Plan
Howdy - where would be the best/appropriate place to ask a VOR related FAA written test question? Looking for help with VOR cone of confusion issues... Cheers!
-mick
-mick
Looking for FAA written help - VOR
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*This* would be a fine place!
Ask away
Ask away
Mick Galvin
Filing Flight Plan
Thanks - didn't want to start spamming the place on my first day ;-)
So I believe I understand VOR radials, to and from indicators and the basics of why there is a cone of confusion (I'm a ham radio guy). My last FAA written practice test came up with 3 cone of confusion questions and I was lost on all 3 and googling for a couple of hours has not helped. I've attached images of one of the questions, related figure and explanation and I just don't get it. Firstly, I thought the VOR was totally unreliable when the to/from was missing. So while I can see that the 030 radial is to the left, I have no idea a) how that's determined to be accurate and b) how I'm supposed to know that the "aircraft is somewhere along the perpendicular line (120/300)".
Really appreciate any help - I'm currently scoring about 80% and I need to get better.... If there is a site I could be reading up on this, please point me there - more than happy to go read.
-mick
So I believe I understand VOR radials, to and from indicators and the basics of why there is a cone of confusion (I'm a ham radio guy). My last FAA written practice test came up with 3 cone of confusion questions and I was lost on all 3 and googling for a couple of hours has not helped. I've attached images of one of the questions, related figure and explanation and I just don't get it. Firstly, I thought the VOR was totally unreliable when the to/from was missing. So while I can see that the 030 radial is to the left, I have no idea a) how that's determined to be accurate and b) how I'm supposed to know that the "aircraft is somewhere along the perpendicular line (120/300)".
Really appreciate any help - I'm currently scoring about 80% and I need to get better.... If there is a site I could be reading up on this, please point me there - more than happy to go read.
-mick
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EdFred
Taxi to Parking
I may have brain f'd. I saw the yellow arrow as a TO arrow. No idea why i thought that. Since it most likely isnt you are missing a to/from meaning you are on the 120/300 radial. Youre right of the 030/210. So SE.
The VOR is only unreliable when you are passing right over the top of it. If you're 25 miles out and you cross the perpendicular radial to the radial you have dialed in on your CDI it will flip to or from to nothing to the other.
The VOR is only unreliable when you are passing right over the top of it. If you're 25 miles out and you cross the perpendicular radial to the radial you have dialed in on your CDI it will flip to or from to nothing to the other.
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Mick Galvin
Filing Flight Plan
This is one critical part I'm missing. Clearly the image shows no to / from so how do I (aircraft) end up on the 120/300 radial?
AggieMike88
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The original "I don't know it all" of aviation.
Direct-enter-enter....
(Oops, sorry, I thought this was the magenta children support group thread)
(Oops, sorry, I thought this was the magenta children support group thread)
Imagine you're flying toward the VOR from the southwest, to the northeast, trying to follow the 030 radial in. If you're right on course, the needle will be centered and the indicator will say "TO". The instant you cross the VOR, it'll still be centered but flip to "FROM". There will be that one moment in the middle when it says neither TO nor FROM.
Now imagine the same flight, but this time you're a little off-course to the right. So the needle will be deflected to the left, saying "Hey, the 030 radial is over there on your left." But it'll still indicate "TO" because it knows you're on the southwest side. You keep flying, and you're still off-course to the right. You keep flying, until eventually you're on the northeast side of the VOR... at this point the indicator will switch to "FROM". The needle will still be on the left, because the radial you've dialed in is still over there. But there will be that moment in the middle, in between when you're "inbound and off course to the right" and "outbound and off course to the right", when the indicator will just throw up its hands and say "neither TO nor FROM". That's how you know that you're crossing a line perpendicular to 030. And with the needle on the left, you know you're on the right side of that perpendicular line, which is Southeast.
Now imagine the same flight, but this time you're a little off-course to the right. So the needle will be deflected to the left, saying "Hey, the 030 radial is over there on your left." But it'll still indicate "TO" because it knows you're on the southwest side. You keep flying, and you're still off-course to the right. You keep flying, until eventually you're on the northeast side of the VOR... at this point the indicator will switch to "FROM". The needle will still be on the left, because the radial you've dialed in is still over there. But there will be that moment in the middle, in between when you're "inbound and off course to the right" and "outbound and off course to the right", when the indicator will just throw up its hands and say "neither TO nor FROM". That's how you know that you're crossing a line perpendicular to 030. And with the needle on the left, you know you're on the right side of that perpendicular line, which is Southeast.
EdFred
Taxi to Parking
It helps to draw it out also. So draw Circle and call that your VOR. Draw a line that represents the 030 120 radial through the center of the circle and extend it to both edges of the paper. Draw a line perpendicular to that line through the center of the circle and extend it to both edges of the paper. Everything on one side of that perpendicular line will indicate to. Everything on the other side of the perpendicular line will indicate from. Everything to the right of the initial line will show a needle deflection to the left everything to the left of the initial line will show a needle deflection to the right. Doesn't matter where you are in any of those quadrants always indicate the same in that quadrant. When you cross that perpendicular line your to from arrow disappears, but the needle deflection still stays to the left or to the right.
Mick Galvin
Filing Flight Plan
OK. I think I see what I'm missing. If I'm in the "cone" area, the VOR is still showing a valid location of me relative to the selected radial but doesn't know if I'm from or to? And as a result, it implies I'm perpendicular to the radial? And given the direction/side of offset to the radial, I can figure which side of perpendicular I'm at?
-mick
-mick
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luvflyin
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It looks like the question assumes you are not right over the VOR in the cone of silence. If you were southeast of the VOR, paralleling the 210 degree radial, heading about 030, when the VOR got just about right off your left wing this is what you would see. You’d be crossing the 120 radial. It would have been TO a couple seconds before this and will be FROM in a couple seconds. If you were in very very close, you could conceivably be South of the VOR, but that wasn’t one of the choices. Woulda been nice if they said you weren’t directly overhead
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Ding ding! Yup...
Still a weird question, IMO. I mean, if you're only two dots deflection, that "switcheroo moment" isn't going to last long...
Mick Galvin
Filing Flight Plan
OK folks - brilliant experience. Thanks so much.
-mick
PS I'll post back when I pass my test!
-mick
PS I'll post back when I pass my test!
dmspilot
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Memorize the following diagram. It's simple enough that it can be memorized with a couple of minutes of effort.
When you take the written test, you will be supplied with scratch paper and pencils. Regurgitate the diagram on a blank sheet of scratch paper and you can use it to answer the questions.
Hopefully the explanation below the diagram is sufficient on how to use it. Rotate the diagram such that the arrow points in the direction that matches the OBS set to the CDI you're interested in. For example, hold the diagram right side up if the CDI is set to 360°, upside down if it's set to 180°, etc. Then simply matching the appearance of the CDI given to you on the test will tell you where the aircraft is.
Although I created this particular pdf, I believe John and Martha King originated the concept.
To answer your question more directly, the TO/FROM flag will go "blank" or "off" when it is getting ready to switch from one to the other, which will happen somewhere along a line that's perpendicular to the OBS setting.
When you take the written test, you will be supplied with scratch paper and pencils. Regurgitate the diagram on a blank sheet of scratch paper and you can use it to answer the questions.
Hopefully the explanation below the diagram is sufficient on how to use it. Rotate the diagram such that the arrow points in the direction that matches the OBS set to the CDI you're interested in. For example, hold the diagram right side up if the CDI is set to 360°, upside down if it's set to 180°, etc. Then simply matching the appearance of the CDI given to you on the test will tell you where the aircraft is.
Although I created this particular pdf, I believe John and Martha King originated the concept.
To answer your question more directly, the TO/FROM flag will go "blank" or "off" when it is getting ready to switch from one to the other, which will happen somewhere along a line that's perpendicular to the OBS setting.
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Mick Galvin
Filing Flight Plan
A very similar diagram was drawn by my CFI during a previous lesson. And as long as I had a from/to indicator the concept was easy and I was fine. Don't know why but the fact that the VOR is showing a valid reference to the selected radial when in the cone was the critical part I was missing. And from there the perpendicular has become clear.
denverpilot
Tied Down
In the FAA questions like that one, you’re just at the cross over point from TO to FROM. You’re not in the cone at all.
In a real dead center pass through the center of the cone of silence, the needle will often go haywire and flop around like a dead fish for a few seconds and TO/FROM may also go a bit haywire.
Don’t think of the TO/FROM flip as being in the cone. That can happen anytime you pass the station.
Imagine this. You’re on foot. You are standing one mile east of the VOR. You have your handheld VOR receiver OBS set to 360.
The needle will be pegged to the left. You would need to fly left if you were attempting to fly this northbound radial to get there.
Your TO/FROM flag would be blank. You’re directly abeam. Thus, not TO or FROM.
If you walk north the FROM flag will appear. If you walk south the TO flag will appear.
Remember when you set the OBS it’s essentially a request for the instrument to answer this:
“If I flew the heading I dialed in, would the station be in front of me (TO) or behind me (FROM)? And would I need to fly left or right to intercept the radial (needle)?”
(When you tuned and faced south and walked south, you weren’t “flying” 360, you were flying 180, and your needle still pointed to your left. Because your OBS was “asking” what you’d need to do if you were flying north, not south.)
Clip4
Final Approach
midlifeflyer
Touchdown! Greaser!
The question is set up to be To/From irrelevant. The needle is deflected in a way that indicates the heading that will intercept the dialed in course is to the northwest - look at the numbers where the needle is deflected. That places you southeast.
VOR reading is one of the very first areas in avionics reading where the methodology used for teaching it is much, much more complicated than actually using the equipment in flight. My recommendation, as always, is a one-on-one with a CFI who understands it well enough to simplify it.
VOR reading is one of the very first areas in avionics reading where the methodology used for teaching it is much, much more complicated than actually using the equipment in flight. My recommendation, as always, is a one-on-one with a CFI who understands it well enough to simplify it.
Mick Galvin
Filing Flight Plan
I've used that a number of times but from what I've seen, it doesn't ever simulate being in the cone of confusion ie it always wants the reading to be accurate.
Right. This is the point that I was missing. Somehow I had it in my head that the absence of the TO/FROM was an indication of being in the cone and given what I initially wrote "I thought the VOR was totally unreliable when the to/from was missing.", I came to a brick wall with the questions. But I'm confident with things now that I've separated the two concepts ie cone and missing TO/FROM are not the same. Again, thanks everyone.
-mick
MauleSkinner
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I think this is the y...it's not that the TO/FROM flag wouldn't show up, its that they chose to simplify the question by not showing it. They only want to know which side of the 030/210 line you're on.
luvflyin
Touchdown! Greaser!
Not necessarily so. When you're in the cone of silence, your VOR reciever doesn't know where you are. You could be flying right at the VOR, when you get close and into the Cone and the Flag goes off you could wrap it into a 60 degree bank and make a 90 degree turn right more into the needle right now and end up on the other side of the radial selected in the OBS. When you get back out of the Cone the needle is going to immediately go to the other side. It's not going to 'swing' from one side to the other as you are passing radials. Not until you are back out of the Cone are you going to get a 'valid' indication. That question is about being able to orient yourself like is displayed in @dmspilot 's diagram in post #14 and understanding the To/From indicator is going to change when you are 'abeam' the station even when you are far from it
luvflyin
Touchdown! Greaser!
Yeah. If the question was about the 'Cone' I'm sure it would have showed the Off Flag
denverpilot
Tied Down
For an official question, maybe. In real life, the thing just goes stupid for a bit, usually. Never seen an OFF flag from flying into the actual RF silent cone, because there’s usually still a little bit of RF signal there.
If you fly over the station perfectly dead center, it’ll indicate a perfect straight up needle, then go insane for a number of seconds, then back to a perfect straight up needle with a flag flip.
Never seen anyone center punch the VOR so well they get an OFF.
Probably a bit receiver specific too. My TO/FROM flag on King stuff takes its own sweet time to flip.
MauleSkinner
Touchdown! Greaser!
I think the OP's confusion is largely stemming from thinking that the TO/FROM flag, or lack thereof, is relevant to the question in any way. It's not.
Mick Galvin
Filing Flight Plan
I think its safe to say that while I thought my problem was with the cone, my real problem was not fully understanding abeam - just as you wrote. The post #14 diagram had been drawn for me by my CFI but @dmspilot 's version had one subtle item that helped me get my head in order and that was the perpendicular line being dashed with the blank/off reference. For whatever reason, that helped fix my thinking.
I'm currently scoring 98->100% in many sections of my test software, just trying to plug some holes and this was a good one. My bad for dragging this knowledge stuff out as far as I have since when I'm done with the test, I'm then able to take my helicopter check ride!
dmspilot
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Disagree. They've done it on purpose, because the flag is actually off. They're not "choosing to simplify the question by not showing it". I've gone over every single written question on VORs on the current test while teaching groundschool. You will not get the correct answer on some of the questions by ignoring an off flag.
luvflyin
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Huh!!! Helicopter?? I thought you was talkin about real airplane stuff. I take everything back.
Let us know how ya did. I thinks ya gots a chance for a 100. good luckMauleSkinner
Touchdown! Greaser!
This isn't ignoring an OFF flag...there is no OFF flag.
dmspilot
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Some indicators are blank in lieu of a flag that shows "off". They are the same thing. If there's no to or from, it's an off flag.
denverpilot
Tied Down
And exactly how did you get the question pool, since it hasn’t been published for years now?
denverpilot
Tied Down
If I remember I can get ya a photo of my King sometime. Or dig through my panel photos here but I doubt I have anything high res enough to see the flag.
MauleSkinner
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Either way, an OFF flag or blank TO/FROM indicates an unusable signal, not that you're abeam the course.
dmspilot
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No it doesn't. In order for what you wrote to be true, the flag would have to change instantaneously, and everyone knows that doesn't happen.
James331
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James331
I’ve found this VERY helpful for teaching and letting students experiment and figure out VORs and HSIs
http://www.luizmonteiro.com/Learning_VOR_Sim.aspx
http://www.luizmonteiro.com/Learning_VOR_Sim.aspx
MauleSkinner
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So what corrections do you make based on VOR indication when the OFF flag is showing?
dmspilot
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Did you stop beating your wife yet?
You don't make corrections. But you can use it to determine your position for the purpose of the written test.
midlifeflyer
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...which of course, is irrelevant to the question since (a) there is no "off" flag, and (b) "who the heck knows? There's no reliable signal" isn't one if the multiple guess answers.
MauleSkinner
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Exactly my point.
midlifeflyer
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Thought so. Just picked your post out of the subthread.
MauleSkinner
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Which is why so many people think the written test is a waste of time...people intentionally remove or add context to make the questions irrelevant.