GravityHater
Well-known member
- Joined
- Aug 12, 2004
- Posts
- 1,168
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
What is the specific difference between these two approaches?
Thanks:
a) "GPS 34"
b) "RNAV (GPS) 34"
these are fabricated examples, not real approaches. just wondering why they are designated as such.
What is the specific difference between these two approaches?
Thanks:
a) "GPS 34"
b) "RNAV (GPS) 34"
these are fabricated examples, not real approaches. just wondering why they are designated as such.
WAAS-enabled IFR approach certified GPS receivers can be approved for LPV and LNAV/VNAV approaches in addition to LNAV approaches, stand-alone(e.g.-GPS) and overlay(e.g.-VOR/DME or GPS) GPS approaches. The advantages of shooting a LNAV/VNAV approach with WAAS instead of using Baro-VNAV for the same approach are that remote altimeter settings can be used and there are no temperature limitations restricting the use of the approach.1. What other types of LNAV/VNAV equipment other than "baro augmented VNAV" is there?
2. Some LNAV-only units ask you to input the alt setting.... and their manuals say they use altitude data to aid the gps in confirming position. If we don't put in an altitude, and only insert the alt setting, how is it getting our altitude?
I have read all kinds of numbers on GPS accuracy so don't feel comfortable quoting any of them.What's the typical error on a GPS postition, 30 feet? Is it the same vertically? If it is, that's better than my altimeter which is typically off by 50 feet when I land.
Yes, but at the same time, I fly out of one airport whose altimeter setting is consitently .04, or 40 feet higher than the airport 10 miles down the road.I have read all kinds of numbers on GPS accuracy so don't feel comfortable quoting any of them.
Re. your altimeter. How can you tell how far off it is unless you know you are on a part of the airport that has been precisely surveyed and the elevation is published? Are you on the correct part of the touchdown zone to use TDZE? Are you at the highest point of all the usable runways to use the published airport elevation? See the problem?
Sorry. I don't understand the relevance of your statement. Local barometric pressure can vary widely over even very short distances. For instance, flying from the coastal mountains in California eastbound out over the hot, dry desert you often can notice a very rapid change in indicated altitude and quite different altimeter settings from one microclimate to the other.Yes, but at the same time, I fly out of one airport whose altimeter setting is consitently .04, or 40 feet higher than the airport 10 miles down the road.
My point was that you are comparing the elevation indicated on your altimeter with some known published elevation. The two most common published elevations are the "airport elevation" and the "touchdown zone elevation." Since no airport is perfectly level you must be at precisely the point where the "airport elevation" or the "touchdown zone elevation" is measured to be able to really ascertain your altimeter error, assuming the exact barometric pressure is set.The point is that you have error either way, if one source is questionable, you can use another to back it up. I don't think we've even mentioned radar altimeter yet.