Where did this come from?
Highflight said:
Sam,
If you're really serious about getting your IFR ticket in your RV, you should know that GPS approaches are being added as time goes on, but a precision approach is best done with a Nav Radio w/glideslope.
Sorry to disagree with you, but that is just plain wrong.... Perhaps you missed a word or two.
GPS approaches are being added all the time is correct, but the whole premise for WAAS GPS is to *replace* the very costly, very aged VOR/ILS system...
Also, let's not confuse GPS approaches with "precision approaches". Or better, let's get educated.
In a VOR/ILS world there are 2 types of approaches, they both use NAV frequencies from a NAV radio. One is a VOR approach and it's considered "non-precision" - this means the the DA (Decision altitude) will be higher than an equivalent approach that is a "precision" approach. An ILS is the later and there are actually various sub categories of it, but as a GA pilot we'll just deal with the one that uses a DH (Decision height above the ground) of 200'
In the GPS world there are actually 4 approaches. A GPS A/B approach the early GPS approaches, they are *all* non-precision approaches and require a GPS device that can perform at the TSO-129a specification. You'll hear them referenced as a certified GPS (also good for enroute too).
Now cross the new technology boundry to WAAS approaches. These require a different reciever, one that conforms to the TSO-145a spec. There are 3 types of approachs here. The first is the LNAV only approach. also an non-precision approach, and it is exactly the same as the TSO-129a GPS A/B approach, same mins, etc. Then there are 2 new approach types, both offering "vertical" guidance via a glideslope, but with differing DA's. The LNAV/VNAV offers glideslope type guidance, but usually (see KSAV GPS 9 approach for an exception) to a non-precision approach altitude (read as not as good as a precision approach). Lastly there is the LPV approach. It's a "precision" approach and in most cases is good to similar ILS standards (usually +50 feet).
The challenge today with GPS recievers is what to buy.... The 300XL, 430, 530, etc are NOT WAAS recievers and only meet the TSO-129a spec (altho Garmin for the last 3 years has said they will update the 430/530 to WAAS). The 480 is a WAAS reciever and it meets the TSO-146a ( a new one because it does LPV which requires meeting both the TSO-145a (the GPS part), and TSO-146a (the Flight Management system part - this included monitoring the internal checks).
One final note. There is also a difference with "primary navigation" vs. "secondary". The TSO-129a only allow for secondary use of the GPS (meaning you'd have to be in radar coverage, or have a Nav radio as well). This is due to the limited integrity checks and having a backup ability if integrity fails. TSO-146a allow for the GPS to be the only and primary navigation means.
Hope all this helps. it's funny that this topic would come up today as I just became educated on all of this as I planned my panel and GPS solutions.
Sorry I picked on Highflight, but let's be clear, and I'm sure this will sound like heracy, the ILS/VOR system as we know it will go away some day, and most likely sooner than later based upon the way the FAA is funding its projects of late. And besides it always bugs me when someone says, learn to fly the ILS and don't worry about GPS..... I think that is *wrong*. Learn to use *all* the facilities that you are given so you have many ways to do the same thing in the case of some sort of ground or air based equipment failure....
