Wow.
A few issues broaught up...
1. Pitot tubes, there are at least 2 one in the front facing forward, and one in the rear facing backwards to airflow. The resultants are coupled.
2. DGPS does rely on ground stations, and is very localized. One must understand that DGPS corrects to the WGS84 ellipsoid model. It is accurate to that model. That model is an approximation of the Earth, so in effect it is accurate to an approximation, which, while getting better, has issues with the bulge of the Earth, especially in the northern/southern latitudes. In addition, I have seen little information on the broadcast range that would make this viable for aviation.
3. As noted before in other threads, the GPS tells the aircraft where it was, not where it is. The Kalman filter is used to estimate where the aircraft is. Due to latency in the GPS signal itself, onboard processing, and other issues, the Kalman filter is required to estimate current position of the aircraft. For reference, a single GPS broadcast from one sat is about 3 seconds long, you need at least 6 for any accuracy, and the sats are not sync'd. Thus in effect, the INS, not the GPS is giving you the current position.
4. Altitude. Depending on the system architecture, the GPS is giving you altitude based on a reference from the horizontal position to the WGS 84 geodetic/ellipsoid. Some units calculate altitude based on actual calculations to the ellipsoid, while others have a simplistic grid placed over the geoid, with a lookup feature. This is more accurate when flying a straight line (and from above) at a constant speed. The system is less accurate in turns, depending on how the individual system architecture calculates geoidal position in a turn. Again, as noted in other threads, the FAA procedure design software did not , and still does not, do a very good job of approximating location while the flightpath turns on an elliptical surface.
5. As Denti noted, GBAS/GLS capability. Localized ILS like guidance. Why this is not on every runway end, and on every aircraft, I just dont know. A failure of the regulatory system is about all I can determine.
Last edited by underfire; 6th Jan 2015 at 09:16.