0
$\begingroup$

I was looking at this approach plate and noticed that SNOWL is an initial approach fix, and that it's charted to be 6.4 NM from the localizer I-IWA.

The only problem with starting my approach from the northwest and crossing over SNOWL is that the localizer does not have DME.

First Question:

How can I fly this approach assuming that I'm coming in from the northwest and want to start from the initial approach fix SNOWL?

Second Question:

If SNOWL is 6.4 NM from, why does the profile view show that it's 5.8 (1.9 + 3.9) NM away from the localizer?

enter image description here

$\endgroup$
3
$\begingroup$

You have a few different points here but the short version is: IWA is a VORTAC and I-IWA is a localizer, i.e. they're different navaids. DME is available from IWA and it's optional but not required for the I-IWA localizer approach. If you do have it, you can use it to identify the ORIYE fix and use the lower minimums at the bottom of the plate, e.g. 1800-1 for category A. If you can't identify ORIYE, you can only go to the regular minimums of 1940-1.


First, I suspect you're confusing I-IWA (a localizer) with IWA (a VORTAC) but they're different navaids that use different frequencies, as shown on the chart. The I-IWA localizer provides lateral and vertical (glideslope) guidance but not DME, which you get from the IWA VORTAC. If you don't have a DME receiver, you could use an IFR-certified GPS instead.

Second, if I understood your question correctly about approaching from the northwest, you're asking how to identify SNOWL without using DME. SNOWL is an intersection ("SNOWL INT") and you can identify it using VOR only, by finding the intersection of any two of these radials:

  • IWA radial 122
  • PXR radial 109
  • TFD radial 028

Third, as far as I can see from the plate, DME is the only way to identify ORIYE (remember that you could use GPS instead of an actual DME unit). When you look at the minimums at the bottom of the plate you can see that the regular category A localizer minimums are 1940-1 but there's an extra set of minimums that you can use if you can identify ORIYE and they let you get lower, to 1800-1. In other words, if you have DME then you can use it to identify ORIYE; if you don't, you ignore ORIYE. Either way, you still have to use the correct set of minimums.

Finally, SNOWL is 6.4 DME from the IWA VORTAC, but only 5.8 DME from the "airport profile" (see the chart legend), i.e. the runway. That means, the runway end is 0.6 DME from IWA (that distance is also shown on the profile).

$\endgroup$
  • $\begingroup$ Sweet, that makes sense. Any idea on why it says in the right-bottom portion of the plate that it's 5.8 NM from FAF to MAP? According to the vertical step-down view, that distance should actually be a little less. The MAP should actually be before the airport profile (I'm splitting hairs here, I know). The dashed upward curved line happens before IWA DME 0.6. $\endgroup$ – slantalpha Apr 30 '18 at 0:21
0
$\begingroup$

the localizer does not have DME.

DME is listed on this chart, so it is available here, though not from the Localizer. The identifier beside the DME flags show the facility that needs to be tuned to get the required indications.

Are VORs always used instead of localizers on approach plates?

(I assume you're asking about the DME source here) No. DME can be located on many different items (VOR, NDB, or ILS). The chart shows which will be used. In this case it's the IWA VORTAC. Some approaches might not have any DME indications at all because there is no DME equipment suitable.

On this chart, waypoints are listed. The waypoint can be identified through various means. SNOWL can be identified either through intersecting VOR radials or by the localizer course with DME from the IWL VORTAC.

the profile view shows "IWA" (is that the localizer or the VOR?) with a DME of 0.6

The identifier next to the distance flag shows the equipment that the DME reference is tuned to. ILS approaches are often paired with DME equipment, so if you have both items available, just tuning the localizer automatically tunes the correct DME. Normally you don't have to know exactly what the distance is to, you just have to match it. In other words, if the DME reads "6.4", you shouldn't assume you're 6.4 NM from a runway.

Is the thick horizontal black bar supposed to be the runway?

Basically. I think the legend defines it as "airport profile".

So if I were to fly this approach, you're saying I should punch in 113.3 into my NAV1 radio, and fly the vertical step-down profile with DME from the 113.3 (IWA VORTAC) station, correct?

It depends on the specifics of your panel. Some optons:

  • Tune ILS on NAV1 and VORTAC on NAV2 (and the DME comes in on NAV2)
  • Tune VORTAC on NAV1, hit "DME HOLD", then tune ILS on NAV1 to bring in the localizer

For an example of a chart where the DME is on the ILS frequency (and you wouldn't have to mess with this), see Las Vegas ILS 26L. On that one, the DME markings on the profile show the ILS identifier (which starts with I-).

enter image description here

Also note that even though the DME is coming from tuning the localizer, it still doesn't read zero at the threshold.

Unfortunately, I feel I've answered some parts of your question, but not the actual "how to identify SNOWL without DME". This is a LOC chart, so it should be usable without DME. I don't see how that part would be done.

$\endgroup$
  • $\begingroup$ Thanks. Are VORs always used instead of localizers on approach plates? And I'm still not understanding the 6.4 NM away from the VOR IWA - the profile view shows "IWA" (is that the localizer or the VOR?) with a DME of 0.6... and it's 0.6 NM away from what? Is the thick horizontal black bar supposed to be the runway? $\endgroup$ – slantalpha Apr 29 '18 at 4:12
  • $\begingroup$ So if I were to fly this approach, you're saying I should punch in 113.3 into my NAV1 radio, and fly the vertical step-down profile with DME from the 113.3 (IWA VORTAC) station, correct? The profile view shows the DME being referenced from IWA, and not I-IWA. If that's the case, why is the 110.15 station (I-IWA) listed as the primary NAVAID (top left) of the approach chart? Sorry for the questions, I just want to make sure I'm understanding it correctly. $\endgroup$ – slantalpha Apr 29 '18 at 6:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.