AOPA Pilot Magazine - July 2021 - 94

P&E ON INSTRUMENTS
The GPS backup
New life for old VORs and ILSs
BY THOMAS A. HORNE
THE GREEN AREAS of
the proposed MON
coverage map show
where 130 airports
will have ILS and/or
localizer approaches.
The 66 airports served
by VOR approaches
are in red. In western
mountainous regions,
changes will be slight,
and most existing
VORs will be retained.
MAKE NO MISTAKE: We live in a world
guided by GPS. And it's not just the flying
world. It's the new standard, for everything
from Google Maps to missiles.
For pilots, that's a very good thing.
GPS offers unmatched advantages. Like
direct-to navigation, and the extreme
precision offered by signals augmented
by the Wide Area Augmentation System
(WAAS), which allows LP (localizer
performance), LNAV/VNAV (lateral
navigation/vertical navigation), and
LPV (localizer performance with vertical
guidance) RNAV GPS instrument
approaches. LP and LNAV-only GPS
approaches-those with lateral-only
guidance-routinely let us descend to
decision altitudes 400 to 500 feet above
runway elevations in visibility conditions
as low as one-half or one mile. LNAV/
VNAV approaches add vertical guidance
that can take us lower than that-usually
250- to 300-foot decision heights.
94 | AOPA PILOT July 2021
And LPV approaches let us descend to
decision heights as low as 200 to 250
feet in visibilities as low as one-half
mile-minimums that match those of
ILS approaches.
Because GPS navigation depends on
satellites, its signals can provide more
airports with more-and more accurate-arrival,
approach, and departure
procedures. Ground-based navaids that
power VHF (very high frequency)-based
VORs and ILSs, and low-frequency-based
nondirectional beacon (NDB) procedures,
are subject to siting effects (for
example, nearby structures, power lines,
or terrain) that affect their accuracy.
Of course, replacing VOR and ILS
approaches with the RNAV GPS variety
was the FAA's whole idea back in
the early 1990s, when the first iterations
of GPS approaches were implemented.
Today, there are 4,078 LPV approaches
serving 1,960 airports, of which 1,191 had
never had ILS capability. Another 730 LP
approaches serve 535 airports, 432 of
which don't have ILS approaches.
But as WAAS-enabled RNAV GPS
approaches grow, ILS approaches hold
steady at around 1,550. For now. As for
the existing 967-strong VOR stations and
their associated approaches, as of 2020
the plan is to cut their number to 589.
And NDBs? The last I heard, some 490
had been summarily shut down in 2005.
Let's just say that NDB approaches continue
to drop like flies, with no end in
sight. You'll look long and hard through
your ForeFlight or Garmin Pilot before
you find one. I hear cheering, and
understand.
MON
For all its advantages, GPS does have
downsides. Signal coverage can be compromised,
and outages periodically
occur. That's why preflight checks of

AOPA Pilot Magazine - July 2021

Table of Contents for the Digital Edition of AOPA Pilot Magazine - July 2021

Contents
AOPA Pilot Magazine - July 2021 - Intro
AOPA Pilot Magazine - July 2021 - Cover1
AOPA Pilot Magazine - July 2021 - Cover2
AOPA Pilot Magazine - July 2021 - Contents
AOPA Pilot Magazine - July 2021 - 2
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AOPA Pilot Magazine - July 2021 - Cover3
AOPA Pilot Magazine - July 2021 - Cover4
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