Flying IFR, Lesson 9
GPS Procedures First, we should note that our GPS in X-Plane is not a true GPS. For our example,
I'll be using an image from the new Elite system. I thought that this lesson would be
appropriate since there are often questions regarding the use of GPS in X-Plane as opposed
to real-world operations. Unfortunately, we won't be able to apply any of this in X-Plane
currently. Through acquisition of satellites in geo-stationary position 11,000 miles above
the Earth(OK, I'm showing off here), a GPS receiver can pinpoint our position over the
ground. There are currently 24 satellites which allow accurate coverage for most of the
Earth. Because GPS can determine position via latitude and longitude, we can specify
``waypoints" which are fixes defined by a latitude and longitude position. They don't
exist, they are simply position fixes which are given names. All of these waypoints are
then put into an electronic database which is in the GPS receiver. Most GPS' have
removable cards which can just be pulled out and replaced when new data is added. Because
the GPS can tell where we are and it knows where the waypoints are supposed to be, it can
tell us which way to fly to get to it. Again, since it uses our position over the ground,
it can tell us our groundspeed. It can also tell us the course we are actually flying
compared to the course we are supposed to fly. Sound familiar? Yes, it's just like a CDI
needle in an OBS or HSI. Most GPS' have their own CDI display on them and many can be
slaved to the aircraft's HSI or OBS. You can see how useful this piece of equipment can be
for us. Because it doesn't use ground-based signals, we aren't limited to flying from one
station to another like using VORs or NDBs. We can also navigate between points that don't
actually exist just as if we were navigating from one VOR to another. For our example, I'm
going to give you an overview on my favorite piece of equipment, the Trimble 2000 approach
GPS. Assume that we were proceeding to Orlando directly and we decide we're going to execute this approach. We would ask ATC for it and, since we can proceed directly to a waypoint, we would ask to proceed direct to ESRAQ(Why go to ORL first when we can go direct ESRAQ?) Now, using the ``WPT" button, we would choose the approach we are going to fly and choose the point we are going to begin the approach at. In this case, we're going to go directly to ESRAQ, but if we chose to get radar vectors onto the approach course, we may get turned in somewhere between ESRAQ and HERNY, the FAF(we'll never get vectored onto the approach after the FAF). So, if that were the case, we would choose HERNY as the IAF so the GPS knew when to move on to the next part of the approach. At this point, you're done setting up and all you have to do is fly. When we hit ESRAQ, we'd enter the hold using the GPS' CDI to track our course. Once we passed ESRAQ inbound, the GPS would switch automatically to HERNY and tell us to fly a course of 070. Once we passed HERNY, it would switch to RW07, the MAP. We would then see the DME readout off the GPS to identify 2.8DME. So, that's really all there is to it. You choose the approach you want to fly, select the waypoint that you will begin the approach at, and then follow the GPS directions. It can also do SIDs and STARs. It's a very handy tool to have on board and it can open up a whole new, more efficient way to fly. If you ever get a chance to use on in real-life, make sure you get your hands on it and really see what it can do.
©
1999 - AVSIM Online and Andrew Ayers |
``1"
shows us our selected waypoint. In this case, we're flying to ORD, or Chicago-O'Ha re
airport. You can see the small ``A" which tells us the waypoint is an airport. If we
were navigating to the Vero Beach VOR, it would say ``VRBv". A MAP would be appended
by ``ma" and so on. ``2" tells us our course to fly to reach the point, in this
case ``156 ". ``3" tells us our nautical mile distance from the waypoint and
``4" tells us our time to reach it based on our current groundspeed, ``5". Our
ground track is displayed at ``6". Matching up the ground track with the course will
take you directly to the waypoint. This way, you don't have to figure out your wind
correction angle. You can just turn to match up your ground track and then read your
heading from the HSI to see what your wind correction is. ``7" is the CDI display. On
course would be with the needle in the middle of the ``O" in the center. There is
also a smaller needle below it which shows how your track compares to the course you're
trying to fly(whether your correction is bringing you back on course or not). ``8" is
the dial which we use to select our waypoint. ``9" is the ``direct" button. Once
we choose a waypoint(ie. ORD), we could push the ``direct" button and the GPS would
immediately show us our course, speed, and time to that point. ``10" is the
``message" button which is used to read messages the GPS is sending. You usually
enter your fuel when you depart, so the GPS will tell you when you don't have enough fuel
to reach the selected waypoint. It can also tell you when it loses signal from another
satellite, when you're nearing an approach, etc. ``11" in the ``enter" button,
used to enter the selected waypoint once it's dialed in with the knob(8). ``12" is
the ``airport/VOR" button which will display the closest 30 airports or VORs. This is
especially useful in emergency situations when you need to find the closest airport.
Simply hit ``APT/VOR" and then hit ``direct" and you're on your way. This is how
I handled my ``lost" procedure on my commercial checkride, much easier that getting
out the charts, plotter, and flight computer. The grey line indicated the database card.
``13" are the function buttons. ``AUX" is used for monitoring system status and
checklists. ``CALC" is used to flight computations such as true airspeed, range,
winds aloft. You must enter in the necessary data(temperature, pressure altitude, etc.).
``FPL" is the flight planning button. By pushing this, you can enter a set of
waypoints to make up a flight plan. You can then just fly along and each time you pass one
of the waypoints, the GPS will tell you that you have and inform you of your new course to
fly. ``WPT" is how you select waypoints to fly to if you're not flying a flight plan.
``NAV" is used to set up a certain course to fly to a waypoint. If you want to go
directly to a waypoint, you can simply choose ``direct", but if you wanted to fly to
a waypoint on a course of 320, you would use ``NAV" to set in the course and then the
CDI would indicate accordingly. This is used for holding and also on some approaches. We
should note that at this time, all GPS approaches are non-precision. GPS vertical
navigation is being studied and surveyed for later implementation. So, now let's take a
look at a GPS approach...
``A" tell us this is the GPS Rwy 7 approach to Orlando Executive. This is
a ``stand-alone" GPS approach since it only says ``GPS" in the approach
identifier. If you look back at the VOR lesson, you'll see that it says ``VOR or GPS Rwy
11R" which means it's a Phase III approach. Looking back to the NDB lesson, you'll
see that it says ``NDB Rwy 11R" with ``(GPS)" below it. This is a Phase II
approach. I'll explain what this means in the end. You'll see that there is no primary
navaid here since this is a GPS-only approach and we won't be using any ground based
facilities. ``B" indicates the Orlando VOR which is ORL, but again it doesn't give
frequency or ID since we the GPS uses lat-long coordinates. This is just a reference
point. ``C" shows us our IAF as the GPS waypoint called ``ESRAQ". It also
depicts our procedure turn. You'll notice that this doesn't look like the procedure turns
we're used to seeing. This ``racetrack" pattern depicts a traditional holding pattern
and must be flown as such. ``D" depicts a feeder route from ORL. ``E"
illustrates our MAP, a GPS waypoint called ``RW07". ``F" depicts another
waypoint which is simply ``2.8NM to RW07". This is not a GPS waypoint you'll notice
as it's depicted by a triangle instead of a star. We only have to look at the GPS to
determine when we are 2.8 from RW07. ``G" is the FAF at the GPS waypoint
``HERNY". ``H" is a fairly unique situation for an approach. You see that it
says ``MAXIMUM 1160ft". On normal altitudes, like 2000ft to HERNY, we can fly any
altitude at or above 2000ft. In this case however, we must be right at 1160ft, no higher.
This is because this approach crosses the approach path to Orlando International.
``I" tells us that our MAP is at RW07. So let's just briefly run through the
procedure we would follow...