Approach question - Unnamed IAF?

B

bhp

Well-Known Member
While looking for interesting instrument procedure to fly in sim, I came across the VOR/DME-C approach at Steamboat Springs (SBS). (http://155.178.201.160/d-tpp/1302/06404VDC.PDF)

I was surprised to see that the IAF points on the DME arc are not labeled fixes, they just say (IAF). Both of the arc segments cross airways, so is the idea you would fly the airway until 9 DME and then begin the approach? Or is this intended as a place to which you would be vectored to begin the approach?
 
bhp said:
While looking for interesting instrument procedure to fly in sim, I came across the VOR/DME-C approach at Steamboat Springs (SBS). (http://155.178.201.160/d-tpp/1302/06404VDC.PDF)

I was surprised to see that the IAF points on the DME arc are not labeled fixes, they just say (IAF). Both of the arc segments cross airways, so is the idea you would fly the airway until 9 DME and then begin the approach? Or is this intended as a place to which you would be vectored to begin the approach?
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You have it correct. As far as I understand it, they don't label fixes on the arc because it's not a fix you would be vectored to, so there's no reason to identify them. You enter the approach phase from the en route phase (from a feeder route) as soon as you enter the DME arc at the IAF.
 
Thanks. I have seen other DME arcs that do have labled IAFs, both on the beginning and sometimes on the middle of arc segments. An example is the ILS or LOC RWY 21 at Roswell Int (KROW). Any idea what the difference is?
 
bhp said:
Thanks. I have seen other DME arcs that do have labled IAFs, both on the beginning and sometimes on the middle of arc segments. An example is the ILS or LOC RWY 21 at Roswell Int (KROW). Any idea what the difference is?
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The difference is, that you can be cleared (for instance, see the RDD LOC-DME (BACK CRS) RWY 16) "Direct GARSA, cross GARSA at 7,000, cleared for the approach, radar services terminated and may God bless and keep you, contact Tower established inbound, buh bye."

http://155.178.201.160/d-tpp/1302/00688LDBC16.PDF

I would suspect that the difference has something to do with radar coverage ("Random RNAV routes may only be approved in a radar environment"). It's possible that SBS does not have any radar and therefore you cannot be cleared direct to the IAF—and must stay on a published enroute segment.
 
It's strange how they do it. I don't think the FAA has a method to their madness. Here are two approaches that have an IAF at PIPES intersection.

RNAV 36 @ KGGG

http://www.airnav.com/depart?http://155.178.201.160/d-tpp/1302/00807R36.PDF

VORDME 31 @ KGGG

http://www.airnav.com/depart?http://155.178.201.160/d-tpp/1302/00807VDT31.PDF

Then we have the VORDME A @ KASL. They just have the 172 radial at 14 DME with no Intersection identifier. However, that location IS where PIPES intersection is as identified by LO ENROUTE charts and by the first two approaches posted.

http://155.178.201.160/d-tpp/1302/05070VDA.PDF
 
Thanks Justin. It's relieving to know that it's not just me who finds this kind of nonsensical. I can't imagine what the downside of identifying the fix with its name is on that approach.
 
I've experienced a similar situation going into the palm springs area. On the way in we fly the SBONO1 arrival which has a fix called JOTNU on the TNP XXX radial at 18 DME. On the way out of Palm Springs we are always cleared to TNP then the 18 DME fix on XXX radial and then our course as filed. Why clear us to JOTNU on the way in but on the way out give us the radial and DME instead?
 
Pay2 said:
I've experienced a similar situation going into the palm springs area. On the way in we fly the SBONO1 arrival which has a fix called JOTNU on the TNP XXX radial at 18 DME. On the way out of Palm Springs we are always cleared to TNP then the 18 DME fix on XXX radial and then our course as filed. Why clear us to JOTNU on the way in but on the way out give us the radial and DME instead?
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I seem to recall that some of those fixes have database names only, that are not to be pronounced or read on the frequency.
 
Autothrust Blue said:
I seem to recall that some of those fixes have database names only, that are not to be pronounced or read on the frequency.
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This is true, however JOTNU doesn't happen to be one of those fixes.

Pay2 said:
I've experienced a similar situation going into the palm springs area. On the way in we fly the SBONO1 arrival which has a fix called JOTNU on the TNP XXX radial at 18 DME. On the way out of Palm Springs we are always cleared to TNP then the 18 DME fix on XXX radial and then our course as filed. Why clear us to JOTNU on the way in but on the way out give us the radial and DME instead?
Click to expand...

I'm not in that area, but I'm going to guess based on similar procedures in my area that it has to do with MVAs in the vicinity of JOTNU. There may be a lower MEA that can be used as long as you are on the radial from TNP. If you are given direct JOTNU, the higher MVA would need to be met.
 
Bernoulli Fan said:
This is true, however JOTNU doesn't happen to be one of those fixes.
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For my own purposes, it's the alphanumeric ones, right?

I'm not in that area, but I'm going to guess based on similar procedures in my area that it has to do with MVAs in the vicinity of JOTNU. There may be a lower MEA that can be used as long as you are on the radial from TNP. If you are given direct JOTNU, the higher MVA would need to be met.
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Having somewhat recently flown the Sonny Bono arrival to PSP, that makes more sense. The terrain there is pretty impressive.
 
ATC will typically have you either fly an airway or a heading until intercepting the arc and then commence the approach from there. No IAF/names needed for that.
 
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