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Flying an ARC
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The Procedure
The DME arc is
a procedure used to transition from the enroute environment to an
instrument approach. It's not a particulary difficult procedure. you will need DME. An arc is
simply a segment of a circle and you will see on the chart that the plotted
arc is exactly that, a segment of an imaginary circle with a radius defined by a DME distance from a VOR.
The DME ARC procedure will take the aircraft from an initial
approach navigation aid and in a wide turn to a position from where you will be
able to continue with the final approach. Below is the DME ARC procedure for
ESOK rwy03 when coming from the East.
- From TESDI fly on KSD
radial 058. There is a restriction in altitude at D16 after that you may
descend to 2500ft QNH, which is the initial approach altitude for the ILS approach.
- At D13 KSD turn left and continue on the D11 ARC. Plan
the descend to be able to keep a speed of 180-230kts when passing this point. The speed is essential, as this procedure will be much more difficult with high speed
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Setting the Insruments
This is the setup on a panel that has a RMI
capable of showing both VHF NAV1 and 2. From TESDI set both VHF NAV on KSD VOR
117.8 and set 238 in the course window of NAV 1. Then follow KSD radial 058 to
DME 13 and turn left until the needles are in the three o´clock position
On
this picture the first turn has been compelted and NAV1 set on the
ILS frequency and inbound radial. The single needle is set on the NDB
SKS, the double needle is VHF NAV2 set on KSD.
This is the point marked 2 on the drawing below.
Continue on the heading 150º until the NAV needle is 10-15º aft before next
turn
This is the point marked 3 on the drawing below.
Now it´s time to turn right again, until the needle is
10-15º in front of the 3 o´clock position. Look at the DME.
It should read approximately 11NM. Plus or minus 1NM is good. If you
get to far out, then make the turn before the pointer is in the back
sector. Keep in at 70 to 80º position and the distance will
decrease.
Same thing if you are getting to close. Keep the pointer in the aft position
instead.
This is a point halfway inbetween point 3 and 4 in the drawing below.
Continue all the way around by turning and waiting for the pointer to move.
Finally, you have reached the turn in position. Shown on the chart as radial
194 from KSD VOR (dotted line).It is time to turn right onto an intercept heading for the ILS. Approximately
355º the ILS inbound course of 025
This is the point marked 4 in the drawing below.
.
Another Example, but using a chart only as reference instead of flight instruments
First, make sure
you have the DME set to receive the VOR. At "A" and "B", we see two IAFs for the two
arcs. "A" would be the IAF for the arc south, since we would be flying
south to intercept course on the arc. This point lies at 7DME along the
345 radial, which also defines V3 between VRB and MLB.
So, if we were
coming southbound along V3, we could go directly from the airway onto the
arc to begin the approach. "B" is the IAF for the arc north, lying at
7DME along the 147 radial, which defines V295 between VRB and STOOP
intersection.
"C" tells us
that this is a 7DME arc, which means that all along the arc, one needs
to maintain 7DME from the VOR. "C" also tells us that we'll be
proceeding along the arc at 1500ft MSL. Next to that, you'll see
"NoPT", which means "No Procedure Turn". Since we'll be using the arc
to intercept the course inbound, there's no need for us to make a
course reversal. Once we intercept the course, we'll just proceed
straight in. "D" shows us our approximate turning point to intercept
our course. You see that both arcs "funnel" into the approach course.
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In case your panel doesn´t have this kind of RMI, you will have to set the appropriate DME VOR on
VHF NAV1 and switch to the ILS freq when starting the final turn. This is not
so good, there is very little time to make that change of freq before you
already passed the LOC.
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In a real aircraft, the turn in radial will be set on VHF NAV2 Navdisplay and
the ILS on VHF NAV1.
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