Curtis L. Olson writes: > I don't know if either DAFIF or FAA could be considered > "authoritative".
I'd consider FAA authoritative for U.S. airports, and DAFIF for other countries, again, until proven otherwise. > I'm guessing that when an ILS is installed, someone goes out and > stands at the center of a runway with something equivalent to a VOR > gauge (or maybe they park a real aircraft out there) and they have the > person at the localizer end adjust the heading until the VOR needle > centers. That wouldn't work -- you need to test it at the appropriate altitude, because of the possibility of interference (the same reason that you have to start the engine before you can test your nav radios on the ground). I watched Transport Canada testing the ILS 07 at CYOW a few days ago -- they NOTAM'ed out the ILS, then sent out their Dash-8 to fly the approach over and over and over again, collecting data. The pilot was quite a cowboy, breaking off the approach literally less than half a wingspan above the runway and rolling straight into a 30-degree bank (I was tempted to go out afterwards and look for paint marks on the pavement). The biggest concern is the approach path, not the runway itself -- the purpose of an IAP is to allow an aircraft to transition from IFR enroute altitudes to a point where the pilot can land it visually, and the approach path has to be guaranteed free of obstructions for a certain distance in every direction. The actual landing, on the other hand, is the one part of the procedure that *is* visual. In a normal Cat I ILS approach, that last possible point to transition to visual will be 200 ft AGL and less than a quarter mile back. For a LOC-only approach, it will more likely be 500 ft AGL and a mile or two back. > What get's recorded and put into the DAFIFT/FAA data could be > *much* cruder or error prone. There are standards for registering navaids with the FAA -- I saw them recently online, but I don't remember where. The lat/lon/elev fields demanded a fairly high degree of accuracy. It's also worth noting that the FAA data is (indirectly, through suppliers like Jepp) the basis for the GPS databases that GA and the airlines use. It might be interesting to look at some examples where the FAA and DAFIF data disagrees -- what are some of the most serious ones? All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
