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then re-transmit the “corrected message”
to your helicopter’s WAAS-enabled re-
ceiver, like the Garmin 430W found in
most newer helicopter instrument panels.
The WAAS-enabled receiver applies cor-
rections and displays navigation informa-
tion based on the information received
from the geostationary satellite and the
basic GPS satellites.
There you have it! The basics of
WAAS! I can hear you asking, but why?
Why all of the juggling of signals back
and forth? Here is “one” of the answers
that you should take to heart; with tradi-
tional GPS receivers we can have an er-
ror of around 25 meters (horizontally)
however, the corrected WAAS position
calculation is usually within 2 or 3 me-
ters! Another huge benefit to WAAS uti-
lization is the money that can be saved.
Because traditional approaches utilizing
ILS/Localizer components can cost the
WAAS’olgy 101
FAA, on the average, over $100,000/year
in maintenance to maintain, it doesn’t take
a math major to figure out how WAAS
can lead to a massive amount of savings.
Understanding WAAS and the alphabet soup of WAAS-enabled
GPS & WAAS Approaches
GPS Navigation!
With the advent of WAAS and the ever
growing progression of its use and avail-
By: Matt Johnson
ability comes a new set of terms we need
to be familiar with. Don’t be intimidated!
What Is WAAS?
The most novice of instrument students
receiver sites throughout the United will recall that we have two “traditional”
If you haven’t heard of WAAS or Wide States. Each site receives GPS signals Standard Instrument Approach types; Pre-
Area Augmentation System, it’s, proba- from all satellites in view. After collect- cision and Non-Precision.
bly fair to say you have been living in a ing information from the GPS satellites Thankfully we now have a third “type”
cave. After all, the FAA “certified” the site then transmits the collected data of approach – the “approach with vertical
WAAS in 2003. Or if you have heard of to a “WAAS Master Station.” guidance (APV for short). WAAS has im-
WAAS but don’t know the in’s and out’s This is where part 1 of the “magic” oc- proved GPS to the point of having landing
because of the intimidation of learning curs. At the WAAS Master Site, GPS er- minimums equivalent to Category I mini-
something new - fear no more! rors are analyzed and a correction mums, i.e. as low as 200 feet AGL. So, if
Let’s get it straight from the beginning message is then transmitted to two geo- this “newer” type of approach has verti-
by looking at WAAS (conceptually of stationary satellites. Stay with me! We’re cal guidance isn’t it classified as a “pre-
course) as “Enhanced GPS.” WAAS- almost there! Part 2 of the “magic” oc- cision” approach? The answer is
based instrument approaches are quickly curs when the geostationary satellites “officially”- NO. “Officially” these types
changing the way aircraft are flown and
YOU need to know the basics. Note that I
said “aircraft” and not “airplane,” which
If you haven’t heard of WAAS or Wide Area
means that this includes your faster than
light instrument training helicopter. The
Augmentation System, it’s, probably fair to say you
beauty of this is that WAAS-enabled GPS
have been living in a cave. After all, the FAA “certi-
receivers can be used for navigation from
TAKEOFF through CAT I precision ap-
fied” WAAS in 2003. Or if you have heard of WAAS but
proaches. Without boring you to tears
don’t know the in’s and out’s because of the intimi-
let’s take a quick look at WAAS from the
“hardware” perspective. The WAAS sys- nadation of learning something new - fear no more!
tem utilizes a series of 38 ground based
24 ROTORCRAFT PROFESSIONAL • Heli-Expo 2010 Preview Issue
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