On 12/25/2008 05:07 PM, James Turner wrote: > What I mean is, for example, EGPH has two > ILS-equipped runways - 06 and 24, but no marker beacons defined at > all. KSFO has some, but for example, 28L has an OM, while 2R has MM > and IM, but no outer. (in nav.dat) > > I've just checked my SimCharts, and apparently neither EGPH approach > plate includes any markers, so presumably the data is right, and the > issue is entirely my fault, for thinking that marker beacons were a > mandatory part of an ILS setup, when they are apparently installed on > a case-by-case basis, and not necessarily as complete sets of OM/MM/ > IM, which again I had naively assumed.
IM is not a required part of a standard ILS in the US or Europe, and has not been for a very long time (if ever). It is used for Category II ILS ... which is rather rare. MM is "normally" part of a standard ILS, but there is no penalty for a missing MM in the US since circa 1990, and in Europe even longer. OM is normally a required part of a standard ILS ... but there are lots of exceptions. A point-out from airport surveillance radar is an acceptable substitute. An NDB (compass locator) is a an acceptable substitute. DME is an acceptable substitute ... and since both approaches to EGPH are "ILS/DME/NDB" approaches, we see that DME is the normal way of flying these approaches, and is a 100% reasonable explanation for the lack of markers. The fine print on the approach plates says ATC will give you radar ranges if you don't have DME. So I don't see anything wrong with the approach plates or with nav.dat in this example. The percentage error rate in nav.dat is not zero, but it is pretty small. My suggestion is that the code should trust nav.dat as to the existence and location of markers et cetera. If nav.dat is wrong, the best way to fix it is to distribute an updated and corrected nav.dat ... not to build second-guessing into the code. ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
