In reading the recent postings, I see there's some confusion regarding glide slope angle vs. glide slope *arc*. While the angle of the GS is typically 3 degrees above the horizon (may vary for terrain, as mentioned previously), the arc that the GS swings tends to be 1.4 degrees, according to the FAA Instrument Training Text. So that makes each "half" of the beam (lower & upper) +/- 0.7 degrees, as I believe was already mentioned yesterday.
If you haven't already, here are a couple references for this: 1) FAA Instrument Training Textbook. This used to be available on the FAA's site, but it has been removed. However I saved a copy to Elite's server, located at this link: http://office.flyelite.com/Junk2/ I encourage folks to grab a copy--it comes in two parts (chap 1-7, chap 8-12). There's also a nice VFR text in that folder, and you can grab that as well. Note especially the information on page 7-30. 2) Airmen's Information Manual (AIM). The same diagram referenced in the Instrument Text can be found in the AIM at this link: http://www.faa.gov/airports_airtraffic/air_traffic/publications/media/aim.pdf Reference the textual description of the GS features on page 1-1-8 (see also figure 1-1-7 on page 1-1-12). So as was mentioned in a previous post, the number of dots on the face of the indicator will determine the degrees per dot on the GS (just do the math). But while we always teach number of degrees per dot on a VOR airway (2 degrees) and localizer (0.5 degrees), I don't recall ever teaching the number of degrees per dot on a glide slope. I do recall the 1.4 degree beam width issue, but not the degrees per dot--it just isn't that important, because full-scale deflection of either the localizer or a glideslope needle on an ILS approach is an instant missed approach. The only real reason we teach it for VOR navigation is basically because at 60nm from the VOR, 1 degree of course is about 1nm off course. So if you are 30nm out and one dot off the center of the airway (which is 4nm wide), you are 1nm off course. Obviously you want to fly the center of the airway though, just as you want to fly both the center of the localizer and glideslope. It should be obvious that it's the safest place to be! Anyway, I hope the above links are helpful to folks. TB ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
