Purpose of Dogleg Airways

iamtheari

iamtheari

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Is there written anywhere an explanation of the rationale of each airway in the national airspace system? There is one particular type of airway that I have seen in a few places that I just don't get. Here is an example:

Between BIS and JMS VORs, there are two airways:

V2 is direct, 82nm long, MEA 4000
V510 is a dogleg, 85nm long, MEA 3900, but MRA at the changeover point of 12000

Why does V510 exist?
 
That may explain some similar situations out there but I don't think it explains this one. Neither airway is over anything but cattle. V510, the dogleg one, goes over a larger wildlife refuge than V2 does - each does overfly at least a corner of one.
 
Dog leg airways are created for many purposes. There could be obstructions along a route that would require a high MEA. They could be created to correspond to sector boundaries within or between ATC facilities. They are used to avoid overflying special use airspace such as MOA, Restricted or Prohibited areas.

One of the most common reasons is to allow for lateral separation between aircraft following the same general routing at the same altitude. They are very commonly used in limited or non-radar environments. Controllers use the FAA manual ATP 7110.65, Section 6-5-2 for the rules to be used in applying lateral separation criteria to aircraft. For lateral separation, the courses must diverge by at least 15 degrees
 
iamtheari said:
Is there written anywhere an explanation of the rationale of each airway in the national airspace system? There is one particular type of airway that I have seen in a few places that I just don't get. Here is an example:

Between BIS and JMS VORs, there are two airways:

V2 is direct, 82nm long, MEA 4000
V510 is a dogleg, 85nm long, MEA 3900, but MRA at the changeover point of 12000

Why does V510 exist?
Click to expand...
To facilitate manual (nonradar) separation.

This is a common occurrence. When the Victor airway system was being set up in the late '40s and '50s enroute ATC radar was pretty rare. There'd be the main airway, V2 in this case, and along it alternate airways to allow aircraft to climb or descend through the altitude of other aircraft. When first established these alternate routes were designated by their position in relation to the main airway; between BIS and JMS VORs the main airway was V2 and the alternate route north of it was V2N. Between INL and HIB VORs the main airway was V129 and the alternate route west of it was V129W.

Note that the MRA at BEHQY is only for the purpose of identifying the intersection using the R-200 of DVL VOR, it's not needed to fly V510.
 
Thanks for the explanations. Looking at it like a railroad passing siding or a highway passing lane makes sense, especially in a non radar environment. Given that some of the last class G airspace above 1200AGL over flat land is nearby, probably the radar facilities in this area are relatively recent.

How do you know the V2A and V129W history? That's something interesting I would like to know more about but don't know where to begin.
 
iamtheari said:
How do you know the V2A and V129W history? That's something interesting I would like to know more about but don't know where to begin.
Click to expand...

I have a pretty good collection of old charts. These images were scanned from the March 2, 1972, Twin Cities sectional.V2N.jpg

V129W.jpg
 
roncachamp said:
To facilitate manual (nonradar) separation.

This is a common occurrence. When the Victor airway system was being set up in the late '40s and '50s enroute ATC radar was pretty rare. There'd be the main airway, V2 in this case, and along it alternate airways to allow aircraft to climb or descend through the altitude of other aircraft. When first established these alternate routes were designated by their position in relation to the main airway; between BIS and JMS VORs the main airway was V2 and the alternate route north of it was V2N. Between INL and HIB VORs the main airway was V129 and the alternate route west of it was V129W.

Note that the MRA at BEHQY is only for the purpose of identifying the intersection using the R-200 of DVL VOR, it's not needed to fly V510.
Click to expand...

Thank you for this post. It's pretty interesting to learn about the history.
 
There are 2 V routes between Ft. Smith and Little Rock, Arkansas. The straight one goes through a restricted area. The dog leg doesn't.
 
I can't even find space for magazines that may someday tell me how to fix my motorcycle. The old chart collection sounds like it would take a lot of space but I envy the information at your disposal.
 
Like has been said it's for lateral separation, mainly a way to get one airplane above or below another. You'll see a lot of fixes on them that are at, or very close to 16 miles and their divergence from the "main" airway is almost always 15 degrees. The trigonometry is that at 16 miles the lateral separation is 4 miles, that's the width of that side of the airway. An airplane is cleared to cross a fix 1000 above an airplane on the other leg on one end, and 1000 feet below on the other end. Or vice versa. A number of years ago someone took it further and factored in DME Slant Range and now 17 or more miles is more common.

Basic lateral separation is that airspace to be protected does not overlap. However, if both aircraft are ESTABLISHED on radials of the SAME navaid, then one of them only need be clear of the airspace to protected for the other
 
luvflyin said:
Like has been said it's for lateral separation, mainly a way to get one airplane above or below another. You'll see a lot of fixes on them that are at, or very close to 16 miles and their divergence from the "main" airway is almost always 15 degrees. The trigonometry is that at 16 miles the lateral separation is 4 miles, that's the width of that side of the airway. An airplane is cleared to cross a fix 1000 above an airplane on the other leg on one end, and 1000 feet below on the other end. Or vice versa. A number of years ago someone took it further and factored in DME Slant Range and now 17 or more miles is more common.
Click to expand...

When was sixteen miles used?
 
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