34 AUGUST 2018 ÇPlane&Pilot
Itall started with on weird note on the ILS Z or LOC Z
Rwy 23 at Walterboro, S.C. (KRBW). he note says:
“GPS and DME required" (emphasis mine).
Back when I learned to ly, a GA airplane with distance
measuring equipment, or DME, was a high-tech ride to
brag over: “It actually shows you how far you are from a
VOR station! And your groundspeed! Well, presuming
you’re lying directly toward or away from the station ...”
Now GPS lets my phone spit times and distances to
four diferent Starbucks dispensaries within the sur-
rounding eight blocks, complete with verbal directions.
Likewise, GPS in the cockpit makes DME an eBay novelty.
You can substitute GPS for a
DME requirement in virtually
every situation—so how can
an approach require both?
It doesn’t. You can fly
this approach with only an
approved GPS. Now come
down the rabbit hole with
me to understand why that’s
true. Spoiler alert: his dis-
cussion might reveal that you’ve been reading approach
charts wrong for years.LETTERS IN APPROACH
TITLES: THEN AND NOW
First, a bit of background: Back when DME was the bomb,
the only single letters you saw in approach titles were from
the beginning of the alphabet, such as the VOR/DME-A
approach to Augusta, ME (KAUG). (hese were also the
days when a cell phone’s only function was making phone
calls. he dark ages, for sure.)
Replacing a speciic runway with a letter in the approachtitle means that only circling minimums are available. his
happens when the inal approach course doesn’t align
within 30 degrees of a runway, the descent from MDA to
the runway would be too steep for a straight-in, or the
runway environment lacks required items for straight-in
minimums. Required items include things like runway
markings and lights. If any of those criteria are true (the
VOR/DME-A at KAUG meets the third one), no straight-
in minimums are published even if the inal approach
course aligns with a runway. Only circling minimums are
published, and the approach is to all approved runways.
You can still land straight-in if you want, but that’s for
another discussion.
Letters from the tail end of the alphabet (X, Y and Z)
identify multiple approaches to the same speciic runway,
so you’ll always see a runway named in the approach title.
Most often, the Z allows lower minimums by requiring a
higher climb gradient for the missed approach. he Y and
Z versions of the ILS or LOC/DME Rwy 19 at Rutland,VT
(KRUT) are poster children for this. he Z version has a
DA 600 feet lower but requires 370 feet per NM on the
missed approach if it doesn’t work out. (he charts for
these approaches have so many notes, the plan view area is
compressed just to make room. Check ‘em out some time.)
he other common reason for multiple versions is
diferent equipment requirements, and that’s what’s hap-
pening at KRBW.
Start with the Y approach. his is a conventional ILS,
with a requirement for DME stated in the notes. he
question is: What for? It can’t be for a transition from the
enroute environment because those notes appear on the
plan view, not in the notes section. he IAF at LAMKE is a
ix on V18-311, so you can get there by VOR. VOR capability
(or GPS equivalent) is assumed, so it’s never stated as a
requirement. An ILS never requires DME for identifying
the FAF or DA because the FAF is glideslope intercept
and DA is by altitude. Cross-check of glideslope intercept
altitude is a good idea, but it’s never required. he missed
approach goes to STOAS, but that can be identiied as an
intersection of two VOR radials.
he answer is that DME is only required for the local-
izer approach. here’s no other way to identify the FAF
at DOTMY or the missed approach point at 1.1 DME on
the localizer. Note that there’s no timing published for
FAF to MAP.
If you’re lying the ILS, you do not need DME on the
aircraft. Yes, that’s correct, if you ly the ILS you may
ignore that note.
Before you press send on the email telling me notes
aren’t optional, understand that this chart displays two
separate approaches, co-charted. he ILS approach is a
diferent approach with diferent obstacle requirements
and diferent procedures than the localizer approach. he
reason they share a chart is historical. Do you remember
paper charts that we used to tote around in hernia-induc-
ing binders? (If not, Google it on your “phone.”) Almost
every ILS had an accompanying localizer approach that
shared most of the same information. Co-charting the twoWhy Would You
Need Both GPS
And DME?
Or would you?
INSIDE IFR
By Je Van West❯ ❯ “Spoiler alert:
This discussion
might reveal that
you've been reading
approach charts
wrong for years.”PORTRAIT: VIRGINIE GARNIER/AGENCY RUSH