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Discussion in 'Flight Following' started by dfs346, Sep 12, 2020.
Pretty sure it was just because VOR begins with V
Do you remember his answer?
Where do you go to find that?
I would imagine that it is because 5 sm either side of the center of the airway equals 4.3 nm. Rounding down seems reasonable and that would give us the 8nm airway instead of the 8.68nm version.
Hmm, LF airways still use the 8.68 NM width. Somewhere along the line, there was a TERPS update for VOR airways from system accuracy lines of 5.0 degrees to 4.5 degrees. Thus reducing the left & right primary obstacle clearance area from 4.34 NM to 4 NM. Of course that’s a minimum. Greater than 51 NM from station the primary area gets larger.
The LAX one was to protect missed approaches which were otherwise going into Class E under the shelf.
Without Surcace Area they would be in Class G there until 700 AGL. Do you know if there was no Surface Area there until 2011? Or was there E that got changed to D then?
EDIT: Gonna leave that typo there. You can decide if I misspelled surface, or circus
I think you're confusing Class A airspace with the Transition Altitude/Transition Level. They happen to coincide here in the US at FL180 but that's not the case everywhere in the world.
And the TAs are lower over there (6,000 in the UK; 5,000 in France) but that has nothing to do with where Class A airspace is.
I looked at the chart. They were identified as Class A airspace. But I looked quickly so I could have gotten it wrong.
Dunno. I didn't read deeply enough to know the previous airspace configuration. I wouldn't be too concerned about an aircraft still being below 700 AGL on a missed or visual go around by the time it were outside the surface area
It could be a little cozy with an approach to 7R if someone was milling around right on the edge with only Clear Of Clouds and one mile visibility. Maybe it was E Surface Area once and they made it D so the Tower could just say no, stay out of there. Setting off TCAS alerts could be a real issue.
To a close approximation, after 2014 the airspace in the UK directly surrounding busier airports like Heathrow is now Class D (it used to be Class A); I haven't been able to find the tops of the Class D. This is overlaid by Class A up to (IIRC) FL 195 everywhere in the country (modulo a few little bits here and there), then Class C above that to FL 600. So quite a bit different from the US — but the ICAO standards aren't about how to apply the various airspace classes, they just define them in terms of clearances, separation, etc. When I flew in Australia it was similar to the UK (assuming I remember that far back ) — Class D control zones inside a large Class C area, with a few weirdo custom-named and custom-built airspaces for the busiest GA airports near Sydney.
This Wikipedia page (which I just discovered) seems fairly accurate: https://en.wikipedia.org/wiki/Airspace_class — all my UK airspace documents are otherwise way out of date .
Department of Transportation library website (needs registration). https://dotlibrary.specialcollection.net/Login
That's the update I'm looking for. Any way I can find the source document?
The source document is the TERPS 8260.3 manual. Not sure when the change occurred but my version is dated in 1976 and it uses the current 4 NM left and right criteria that we currently use.
LF airway obstacle tolerances
VOR airway obstacle tolerances
The 8260.3B CHG 26 document in the DOT Library has those same diagrams on Page 264 (attached) but the date in the top left corner is 02/24/2014. Does your copy have a 1976 date in that corner? If so could you kindly post the whole page? Many thanks
Mine is a copy of the original but it’s 8260.B CHG 7 dated 12/6/84.
I think I narrowed down the date of the change from 10sm to 8nm width, to the period between 06.28.1962 and 08.18.1969. By the latter date the 8nm width was in place (as per attached file, page 23, paragraph 2).
Part 71 specifies the dimensions. Can't you look up historical FARs as of any date on the FAA's website? I have a 1965 version and they list 4 NM and 4.5° beyond 51 NM.
Many thanks. For my purposes, I think the Advisory Circular of 08.18.1969 is sufficient. I am investigating an incident that occurred in 1971 and I wanted to establish the width of Victor airways that prevailed at that time. It seems reasonable to assume that the width did not change between 1969 and 1971.
I did look up the historical FARs on the FAA website, but in Part 71 I did not find anything earlier than 1991.
If you could post the relevant page from your 1965 edition, that would be a big help.
Eh? LF/MF-based airways are not the same thing as VOR-based Airways."
They were always different with regard to the width."
LF was 5 SM, VOR was 4 NM.
That’s what I was thinking, always been 4 miles. If at one time they used 5 degrees +/- error factor, instead of 4.5, it would just have moved the point where the ‘secondary’ area started from 51 miles to something closer.
Well the OP has a reference that states Victor Airways used to be 5 SM wide on each side. So either they changed or that reference is incorrect.
I think it all just boils down to when they changed from Statute to Nautical and rounded off. As far as ‘Terping’ them, yeah, they going to be using decimal points.
No, he has one image showing the width of a LF-based airway and another showing a VOR-based airway. The ground based navigation upon which the airway was determined different. Most likely it was the transition to VOR navigation that changed it from SM to NM. But it does indeed predate the late 90's for sure. It was 4 NM when I started flying in 1981.
Ok, I don’t know what you’re talking about. I posted the two different airway diagrams showing the differences in how both airway widths are currently determined.
The OP posted an FAA historical document from 1952 quoting a Victor Airway width of 10 SM. That’s obviously different from our current criteria. So again, his quote is either in error or at some point the width changed after 1952. I don’t have documentation from that time so I can’t confirm that quote. That’s the whole point of the OP’s post. He’s looking for further evidence in supporting the historical document.
I don’t think it is as simple as looking at TERPS criteria to determine what the width of the airway is. Yeah, there is a very close relationship. Like @dtuuri said above, FAR 71 determines the width. Yeah, TERPS works from this base point. For instance applying primary and secondary criteria. The pics posted above in #56 could seem to imply that 51 miles is the starting point and then you plug in the angle and the result is width. 51 miles is the ‘result’ of applying angle to width.
It is as simple as TERPS criteria in getting airway widths. That’s how they determine not just the primary and secondary obstacle areas, but the width itself. That’s based on (VOR) a 4.5 degree accuracy 95 % of the time. We as IFR pilots are just taught the dumbed down 8 mile airway width. But there are some cases (greater than 50.8 NM) where the actual width and the class E that goes with it, is expanded.
Gotcha. What I was making reference to was the 'basic' width. The width less than 49.66 from the Navaid on LF/MF and 50.8 on VOR. The minImum width so to speak. I don't know how they determined what the minimum width should be. But they are not a result of starting out with 49.66/50.8 and 5.0/4.5 degrees. The 49.66/50.8 are a result of doing the trig starting out with 4.3 miles and 5 degrees or 4 miles and 4.5 degrees. They have to use all of that to Terp them out to determine MEA's and MOCA's.
Further to a FOIA request to the FAA, I received the answer, as follows:
"The final rule was published on July 7, 1964. Section 71.5 established the width of 4 miles either side of centerline. Section 71.19 adopts nautical miles as the measurement. Both sections are on page 8472 of the rule, which I have attached."
You really dug deep. Why did you want to know?
I'm writing a book on an incident which occurred in 1971. For this purpose it was important to know the width of Victor airways at that time.
D. B. Cooper??
Let's say: Flight 305.