DME arcs, how do you fly to the IAF?
Gregory R. TRAVIS
defined by the arc itself and a crossing radial from a nearby VOR (usually
co-located with the DME facility).
However, there is often, as far as I can tell, NO published way to get to the
IAF and/or ONTO THE ARC!
Case in point, right here at my own beloved BMG, we have a VOR/DME runway
35 approach. One way to get on the approach is via a 12-mile DME arc.
The arc has two points labeled as IAFs, both defined by radials off the
co-located VOR.
HOWEVER:
The radials intersect the arc at points that are NOT on any airway
The intersection points are also not defined on approach or
enroute charts as 5-letter intersections
The radials themselves do not define any airway
The plate nomenclature, both Jepp & NOS, do not have any standard
"transition route" from the VOR - i.e. the radials are
depicted with thin lines and there is no distance or
minimum altitude printed alongside the radial
The DME arc is not labeled "Radar Required" (i.e. the assumption
is that, somehow, you can get there w/o radar vectors
So, fellow pilots, how do you get TO the IAFs? It's easy to get to the
VOR itself - many airways use it. But from there to these "point in space"
IAFs seems to be a mystery.
Sure, I know what you would do, pragmatically: You would fly to the VOR
and then outbound on one of the radials defining an IAF at an altitude
you felt was "safe" - about 2500' I would say.
But, and I'm always interested in legalities, say you found yourself:
1. Needing to fly this approach
2. Totally unfamiliar with the surrounding terrain, and with no
sectional charts. For all you know, there are 11,000' mountains
all around and the airway that you just flew (which has a minimum
altitude of 3,000') to the VOR managed to snake you through a very
narrow valley.
3. In IMC
How could you fly to one of the IAF's on the arc?
greg
--
Gregory Reed Travis D P S I
Data Parallel Systems Incorporated gr...@cica.indiana.edu
James Hanrahan
I confirmed my past practices by consulting my Jeppesen Instrument Training
Manual, third edition, 1989, page 4-12:
"DME arc transitions may be started from any airway or authorized
direct route which intercepts the arc. There is no requirement
that the arc transition must begin at the designated IAF."
So if the airway you are on crosses any part of the arc, or if the
controller clears you direct to any fix and the route crosses the arc,
and you are cleared for the approach (or cleared to intercept the arc),
you may intercept the arc "inside" the charted IAF for the arc.
Jim Hanrahan, Code 822 COM/ASEL/IA
hanr...@oasys.dt.navy.mil PA28R/T34B
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(0x(B[1m Jim Hanrahan CDNSWC Code 822 [0m(0x x(B
(0x(B[1m hanr...@oasys.dt.navy.mil [0m(0x x(B
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Gregory R. TRAVIS
> I confirmed my past practices by consulting my Jeppesen Instrument Training
>Manual, third edition, 1989, page 4-12:
> "DME arc transitions may be started from any airway or authorized
> direct route which intercepts the arc. There is no requirement
> that the arc transition must begin at the designated IAF."
>So if the airway you are on crosses any part of the arc, or if the
>controller clears you direct to any fix and the route crosses the arc,
>and you are cleared for the approach (or cleared to intercept the arc),
>you may intercept the arc "inside" the charted IAF for the arc.
A-ha! Thanks, Jim! I suspected, as did a colleague, that arcs could
be begun anywhere INSIDE the IAF, but could not find any supporting
evidence in Part 91, nor the AIM. And I seem to have misplaced my
copy of the TERPS :-(...
It's interesting that the wording, quoted above, contains the word
"transitions" - I'm assuming it doesn't count then, when the arc is not
a transition, but the actual approach as in our Martin State example.
Furthermore, in the BMG case, there is only one airway intersecting the
arc and it's on the west portion of the arc. Interceptions at any
other point would require a direct vector which requires, naturally, either
controller co-operation (implies radio contact), or knowledge of the
surrounding terrain.
Bruce Bateman
>
> I confirmed my past practices by consulting my Jeppesen Instrument Training
>Manual, third edition, 1989, page 4-12:
>
> "DME arc transitions may be started from any airway or authorized
> direct route which intercepts the arc. There is no requirement
> that the arc transition must begin at the designated IAF."
>
>So if the airway you are on crosses any part of the arc, or if the
>controller clears you direct to any fix and the route crosses the arc,
>and you are cleared for the approach (or cleared to intercept the arc),
>you may intercept the arc "inside" the charted IAF for the arc.
>
Regarding the situation where there is no charted means of getting to
the IAF on the approach plate. I recall this situation being discussed
in my inst training and it turns out that in many cases when there is
no shown transition to the IAF on the approach plate or via a STAR,
the IAF coincides with a fix (intersection or whatever) on the enroute
or terminal chart. This means you have to cross chech the plate with
the chart which is awkward, but the means of getting to the IAF is
actually there.
Bruce Bateman
John L Bishop
>I've seen a number of DME arc approaches that specify the IAF as a point
>defined by the arc itself and a crossing radial from a nearby VOR (usually
>co-located with the DME facility).
>
>However, there is often, as far as I can tell, NO published way to get to the
>IAF and/or ONTO THE ARC!
>
>Case in point, right here at my own beloved BMG, we have a VOR/DME runway
>35 approach. One way to get on the approach is via a 12-mile DME arc.
>
>The arc has two points labeled as IAFs, both defined by radials off the
>co-located VOR.
<stuff deleted>
>So, fellow pilots, how do you get TO the IAFs? It's easy to get to the
>VOR itself - many airways use it. But from there to these "point in space"
>IAFs seems to be a mystery.
>
>Sure, I know what you would do, pragmatically: You would fly to the VOR
>and then outbound on one of the radials defining an IAF at an altitude
>you felt was "safe" - about 2500' I would say.
>
>But, and I'm always interested in legalities, say you found yourself:
> 1. Needing to fly this approach
> 2. Totally unfamiliar with the surrounding terrain, and with no
> sectional charts. For all you know, there are 11,000' mountains
> all around and the airway that you just flew (which has a minimum
> altitude of 3,000') to the VOR managed to snake you through a very
> narrow valley.
> 3. In IMC
>
>How could you fly to one of the IAF's on the arc?
Greg,
Use the Minimum Safe Altitude. In the case above, this would extend from
the VOR out to 25 miles. Simply fly outbound from the VOR at or above the
published MSA, and let down on the arc when established!
Also, don't forget the sectional charts! They are very handy in keeping you
informed about the terrain.
John
--
Standard Disclaimer: These are my comments, and not necessarily my employer's.
John L. Bishop, Tech. Manager, Intergraph Corp. jlbishop@.ingr.com
CP-ASMEL,IA C-340II N69480
Merrill St. Marys
>In <71...@oasys.dt.navy.mil> hanr...@oasys.dt.navy.mil (James Hanrahan) writes:
>>So if the airway you are on crosses any part of the arc, or if the
>>controller clears you direct to any fix and the route crosses the arc,
>>and you are cleared for the approach (or cleared to intercept the arc),
>>you may intercept the arc "inside" the charted IAF for the arc.
>"transitions" - I'm assuming it doesn't count then, when the arc is not
>a transition, but the actual approach as in our Martin State example.
The airport where I work (CYFC) has an arc transitions to 2 approaches:
an ILS 15 and a VOR 09.
The VOR 09 has clearly defined IAF points (one for each side arc)
where the arc meets an airway, and an IF at the point where the
closest arc joins the final course. The FAF is a named DME point
(but not shown as an intersection) on final. Most aircraft doing
the straight-in approach fly to one of the IAFs, and then turn
direct the FAF (for a 20-degree intercept). In most cases, the
approach is started much earlier, as Center will usually clear the
aircraft direct to the FAF from 40 miles out.
In the case of the ILS 15, however, there IS NO IAF. The IF is an
un-named DME fix on final, and the FAF is an NDB. As usual, there
is a "No PT" altitude depicted for any aircraft arriving at the IF
from "outside" the approach. Aircraft are routinely cleared to
the arc, and apparently are allowed to intercept it anywhere before
the lead radial, although most aircraft will continue inbound to
where the arc crosses their airway unless given a vector. One
common situation is where an aircraft is already inside the arc--
one of the airways has a 80-degree turn from north to west, 10 DME
to the east. Rather than have northbound aircraft turn west, proceed
to the VOR, transition to the NDB and do a full procedure, Center
often allows them to fly 330 (parallel ILS) to intercept the arc
from the inside.
Anyway, our charts are about to get a bit more complex here in Canada-
most companies have defined "center-line fixes" in their RNAV
computers, and have been asking for clearances "direct the CLF",
which Center can't directly approve as the fix isn't on any charts.
This means asking the pilot where *his* company's CLF is as a LOC-DME
or radial-DME fix, and then clearing him direct to that point. Since
this is so time consuming and error prone, Canada has decided to add
a new CLF to *every approach* for which a straight-in is possible.
The new CLF will be named, and will be a constant distance from the
threshold for all approaches.
Chris. PP-SEL, ATC. Canada.
Ob-Disclaimer: my opinions don't represent the views of Transport Canada.
Mark Laubach
: Use the Minimum Safe Altitude. In the case above, this would extend from
: the VOR out to 25 miles. Simply fly outbound from the VOR at or above the
: published MSA, and let down on the arc when established!
The MSA's are really for emergency situations only, right? Navigation
signals are not guaranteed at the sector MSA. You might be above the
MSA in the sector but not be able to receiver either the VOR or DME.
I would suggest using the minimum altitudes in the approach charts.
Mark
PP-ASEL/IA-G/AT