The mind boggles at the Notams & Chart Changes this will cause
Thread Starter
Join Date: Aug 2002
Location: Australia
Posts: 56
Likes: 0
Received 0 Likes
on
0 Posts
The mind boggles at the Notams & Chart Changes this will cause
But, the local datum is changing because Australia has literally moved, doesn't that mean that an airport, for example, is not at the same WGS84 coordinate now as it was 10 years ago?
Apologies for the thread drift, but.....
I seem to recall reading somewhere that Australia tried to set up it's own "GPS" system based on the ITRF before adopting WGS84.
China's airfields are not all referenced by WGS84, meaning that not all arrivals, or departures, in an FMC actually line up. So if you try using LNAV/managed mode to intercept an ILS localiser it is quite possible that you will just parallel the actual localiser, you need to use a heading mode. Similarly when parked on the ramp, a runway actually behind you will appear in front of you on your EFIS NAV screen. Dalaman was a particular case in point.
Not only is Australia moving in a North Easterly direction as a whole, but it is not moving uniformly. Western Australia has moved more than say NSW, Victoria and Tasmania. Imagine putting a pin into the middle of Australia, somewhere around Alice Springs, then Australia is generally moving NE, but it's also rotating clockwise about the "pin" in Alice.
I seem to recall reading somewhere that Australia tried to set up it's own "GPS" system based on the ITRF before adopting WGS84.
China's airfields are not all referenced by WGS84, meaning that not all arrivals, or departures, in an FMC actually line up. So if you try using LNAV/managed mode to intercept an ILS localiser it is quite possible that you will just parallel the actual localiser, you need to use a heading mode. Similarly when parked on the ramp, a runway actually behind you will appear in front of you on your EFIS NAV screen. Dalaman was a particular case in point.
Not only is Australia moving in a North Easterly direction as a whole, but it is not moving uniformly. Western Australia has moved more than say NSW, Victoria and Tasmania. Imagine putting a pin into the middle of Australia, somewhere around Alice Springs, then Australia is generally moving NE, but it's also rotating clockwise about the "pin" in Alice.
Join Date: Aug 2013
Location: PA
Age: 59
Posts: 30
Likes: 0
Received 0 Likes
on
0 Posts
Not certain about that in China. All of the procedures that have been designed for RNP are based on WGS84 datum. I will agree that there is little data, and Jepp frequently had the locations incorrect. The new runways such as Lhasa/Lhiza had to be surveyed, and that was WGS84. (SRTM data then ground verified)
As GPS navigation has evolved, so have the standards. The work in the US was problematic as well, even though the the datum and survey standards were good, the standard was to survey the end of the RWY, NOT the threshold. This lead to significant differences in many locations.
KPSP current RW endpoints from FAA:
KBOS:
In AUS, same thing, the datum for the design has used WGS84. Not to say that the locations were correct either, but at least were a little better.
AUS was the same way when I did MEL, and it took a while to move the RWY location to threshold, but now they are all pretty good.
YMML:
Back to the thread, the RWY endpoints and coordinates are constantly surveyed and updated, and verified/validated each cycle. Much the same as the magvar is constantly checked, and rwys renamed accordingly.
As GPS navigation has evolved, so have the standards. The work in the US was problematic as well, even though the the datum and survey standards were good, the standard was to survey the end of the RWY, NOT the threshold. This lead to significant differences in many locations.
KPSP current RW endpoints from FAA:
KBOS:
In AUS, same thing, the datum for the design has used WGS84. Not to say that the locations were correct either, but at least were a little better.
AUS was the same way when I did MEL, and it took a while to move the RWY location to threshold, but now they are all pretty good.
YMML:
Back to the thread, the RWY endpoints and coordinates are constantly surveyed and updated, and verified/validated each cycle. Much the same as the magvar is constantly checked, and rwys renamed accordingly.
Moderator
It is a real worry that New Zealand is getting closer....... 
