question about DME ARC

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eng4ksa

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eng4ksa
Hi,

I have a question regarding a DME ARC. If the controller told me to fly a certain heading to join the DME ARC, what should I do with the HSI needle? should I center it and turn to make it 90 degrees? or leave it as it is? ( attached the DME ARC I'm using )
 

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eng4ksa said:
Hi,

I have a question regarding a DME ARC. If the controller told me to fly a certain heading to join the DME ARC, what should I do with the HSI needle? should I center it and turn to make it 90 degrees? or leave it as it is?
Click to expand...
I would place it on the next 10 degrees in the direction of the arc and then lead the turn toward perpendicular based upon ground speed. Ex.) Given "Fly heading 360 to join the 10 DME arc counterclockwise (from the south on approx R-180)." I would set the HSI to point 350 so it will center as you cross the R-170. Then, I would lead the turn at about 10.5 (100ish kts) and turn eastish with wind correction. HSI would then be set to show me crossing the R-170 next.
 
The heading was probably not perpendicular to the arc. So, unless I already knew where I was relative to it, I would first center the needle for situational awareness. Then, as I got close to the intercept I would center it again to find the radial where I would likely intercept. 90 degrees to that radial is my initial target heading on the arc. And 10-20 out in the direction of the arc will confirm the entry after turning.

Draw it out and I think you'll see what I mean.
 
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Yeah... the only way to know, initially, would be to orient it to the station. DME arcs can be ugly.
RMI's make them easier (do they still make those?).
 
If you are going to interecept an arc (and not do it with a GPS that has the arc) you pretty much have to fly towards it on a radial leading to the VOR that defines the arc. Then you will turn 90 degrees and be on the arc.

So long as you are on a radial that is defined by the VOR that defines the arc, your turn to the arc path will always be 90 degrees. Try drawing it with ruler and compass.

If you have a navigator he could figure out the intercept from any angle with a protractor.
 
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coloradobluesky said:
If you are going to interecept an arc (and not do it with a GPS that has the arc) you pretty much have to fly towards it on a radial leading to the VOR that defines the arc. Then you will turn 90 degrees and be on the arc.

So long as you are on a radial that is defined by the VOR that defines the arc, your turn to the arc path will always be 90 degrees. Try drawing it with ruler and compass.
Click to expand...
You really don't need to do 90°... easier, but not at all required.
 
I have never flown a DME arc with an HSI installed. Flying with with a VOR head, I have always done them like coloradobluesky said to do it. Not sure about flying it with an HSI. I wish I could be more help.
 
You can figure out the arc intercept at any angle with a protractor though. You do have a table, compass, ruler and protractor on board don't you?

Yes you can guess, and wiggle it in.
 
If they give you a heading to join it you gotta do that. You can't just decide to turn direct to the VOR and do the 90 degree thing because that's what you're used to. I'd do what's been said above, fly the vector, when you get to the specified DME, twist and identify the radial you are on and take it from there. Unless your disoriented, you should have a pretty good guess what your first turn should be to get started while you are identifying the radial you are on.
 
Keep in mind that approach plates are oriented to TRUE north. I checked the government ones, don't think they have changed. Not sure about the Jepps. Somebody check that out. See, what you need is the course in degrees of the tangent at the intercept point. You know its 90 degrees to your course if you are on a radial of the VOR that defines the arc.
 
somorris said:
I have never flown a DME arc with an HSI installed. Flying with with a VOR head, I have always done them like coloradobluesky said to do it. Not sure about flying it with an HSI. I wish I could be more help.
Click to expand...
Ain't no different. Ya center the needle. Read the compass card. You have to know your FROM's from your TO's of course, just like a CDI. The needle will be oriented more horizontally than vertically
 
It's easy if you have a moving map, just drive around the magenta curve like you were driving on a curved road. :)

Frankly, even with my old KN64 DME, it wasn't hard to bracket my heading based on whether the numbers were getting bigger or not (it reads in tenths of a mile). One amusing thing you can do if your DME supports it is set the thing to display the "ground speed." If you're precisely tracking the arc, that is going to be zero.
 
With my 480 it's easy. I would join it just like any other segment of the approach - sequence to it with a FlyLeg as I was getting close, then just center the CDI and keep it centered.

Just saying you're using an HSI as opposed to an ordinary VOR-head-with-CDI doesn't give enough information. It really depends.
 
Kritchlow said:
Yeah... the only way to know, initially, would be to orient it to the station. DME arcs can be ugly.
RMI's make them easier (do they still make those?).
Click to expand...
Many glass panels have RMI-like displays. On a G1000 PFD, you have a softkey on the PFD to turn each VOR on, displayed underneath the CDI.
 
Just a WAG - the OP involves a situation without a GPS or moving map. Sure. Piece of cake with an iPad too. And even legal.
 
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