Luke
So do any of you guys have any info relevant to this KTM accident? Or is this willie-waving?
If the KTM A330 was not aligned with the runway centerline, due to an rnp offset as discussed here, it could have contributed to this incident. It is a possibility to consider.
However, having mentioned these innacuracies of the GNS approach system, various critics came out of the woodwork claiming that GNS is a navigational panacea that is never wrong. And they are still claiming that GNS works to the accuracy of the ANP, when ANP is only the performance at this moment in time. Clearly, some operators need to set up training programs to discuss the design, operation and pitfalls of the standard GNSS approach system.
The known inaccuracies of GNSS is why the WAARS and EGNOS augmentation systems are being developed. Why spend all that money on a new augmentation system, if the original GNS is always 100% accurate? Answer - it is not that accurate, which is why it says 95% accurate on the tin.
P.S. Yes, the orbits of the satellites stay fixed, while the Earth rotates underneath them, just as I said. So the azimuth and declination of the satellites is constantly changing - with satellites setting behind the hills as you make the approach.
Below is a nice GPS satellite animation.
Note that the orbits remain fixed, resulting in an ever-changing azimuth and declination of the satellites your receiver is tracking.
The blue satellites are the ones that are visible. Note the changing number of satellites visible, and remember that this number will be less in high terrain.
The green lines indicate the azimuth and declination of each satellite. Note how satellites drop behind the horizon and are then deleted.
Remember that satellites in the zenith (overhead) provide little or no lateral navigation input, while those on the horizon are subject to refraction errors.
ok 465
Actually GLS and WAAS are two different animals.
No they are not. WAAS and EGNOS are both GBAS (ground based augmentations systems) for GNSS approaches.
A GNSS approach plus a GBAS equals a GLS. So they are all part of the same system - a system that will eventually eradicate the errors being discussed here.