Entering DME Arc

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John777

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Most of the approaches consists of 90degree intercept, but what if ATC instructs us to join DME arc from current heading, 45 degree intercept, or even 30.. etc ?


Johnny.
 
I'd request to come in on a radial. The intercept on ANY radial that comes off the same VOR that the arc uses is always a 90 degree turn. Anything else can be figured out, theoretically. But its subject to error due to wind and compass error. Its basic geometry, but who has a drafting board on the airplane to figure it out?

I don't think ATC would issue an intercept to an arc unless it was on a radial from the VOR that defines the arc, though I can't site chapter and verse on why not.
 
Just guestimate and adjust. Or just track what radial your on and 90 degrees from there.
 
John777 said:
Most of the approaches consists of 90degree intercept, but what if ATC instructs us to join DME arc from current heading, 45 degree intercept, or even 30.. etc ?


Johnny.
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Not gonna happen. Don't worry about it.

Bob
 
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Bo says

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It's quite easy (got caught in that myself once). Just twist your VOR to the radial you are on and note 90 degrees from here left or right - depending on the arc turn. This is your new heading to turn to. Usually I underturn 5 degrees, though.
 
There are three ideas here.
1. Entering the arc on the radial depected on the chart. That is a 90 degree turn.
2. Entering the arc on a radial that comes from the same VOR that defines the arc. That is always a 90 degree turn.
3. Entering the arc on a heading that is NOT on a VOR radial that comes from the VOR that defines the arc. That is some angle turn that is NOT 90 degrees.

You're not going to get #3. Ive had an instructor give me #2 and been told its possible to get it from ATC. #2 is certainly doable.

Don't do approach entries or hold entries that wont happen with ATC. You start doing that and you start thinking that's how things really work and you try and do it in an ATC environment and you just end up confusing yourself and those around you. Its not that a pilot might not be able to wiggle it in and do it. Its that you wont ever get that from ATC. Pilots actually do for real what they practice. So practice it in a way that is actually done.
 
I have entered arcs off headings in real life both in my plane and at work. So it can and does happen. How often I couldn't tell you but there is one Airport in my airlines network that every single time I have flown into it I've joined the arc for the approach from a heading
 
Yeah, I'm not a wizard when it comes to rules about how it's *supposed* to happen, but MYNN is an example of where I'll commonly get a heading to join the arc upon being cleared for the approach. At a minimum I've always had an RMI, or even better an FMS with the arc available, so it's never been a big deal. In fact, my current FMS has a specific procedure for setting it up to capture the arc from a heading.

Now whether or not all this is technically correct, I'll let the guys smarter than me argue about that. :)
 
Its a DME arc, maintain heading till your .5 out, put the VOR station off the appropriate wing, then fly the arc. Don't understand the problem.
 
wilkersk said:
Its a DME arc, maintain heading till your .5 out, put the VOR station off the appropriate wing, then fly the arc. Don't understand the problem.
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The problem is looking for individual trees and not seeing the forest.

In the rare event of such an instruction, yep, it's as easy as the technique you describe or another one that fits more with the way this stuff is usually taught: center the VOR upon reaching the DME distance to determine the radial you are on at that point. Turn 90 degrees to it in the proper direction, and you are ready to "twist 10 turn 10" or use whatever monitoring procedure you like.
 
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wilkersk said:
Its a DME arc, maintain heading till your .5 out, put the VOR station off the appropriate wing, then fly the arc. Don't understand the problem.
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Yeah. Ain't no thing. Fly the heading. When you get the right DME, have the needle centered. Now you know where you are. Only thing different from the typical entry is the initial turn is something different than the usual 90 degrees
 
luvflyin said:
Yeah. Ain't no thing. Fly the heading. When you get the right DME, have the needle centered. Now you know where you are. Only thing different from the typical entry is the initial turn is something different than the usual 90 degrees
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Just to avoid confusion (since the question presupposes confusion ;)), the number of degrees the aircraft will turn will be different than 90 degrees. The initial heading you turn to will still be 90 degrees to the radial you centered to.
 
midlifeflyer said:
Just to avoid confusion (since the question presupposes confusion ;)), the number of degrees the aircraft will turn will be different than 90 degrees. The initial heading you turn to will still be 90 degrees to the radial you centered to.
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Yup
 
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