Most pilots now have GPS, moving maps, and flight directors/autopilots-all of which provide great safety advantages. Otherwise, a quick call to ATC or Flight Watch may give you the latest weather. Call up the weather on the AWOS or ATIS frequency, if the airport has one. The glideslope may be out, for example, in which case you’ll be shooting a localizer-only approach with no vertical guidance-and thus have to comply with higher minimums. You should have checked during the preflight briefing to learn if any components of the ILS are inoperative. Take a good look at the approach chart, noting everything-but paying special interest to minimum altitudes. (In nonradar and/or nontowered environments, “full” procedures can be the rule, leaving you to navigate to the ILS’ via feeder and initial fixes on your own.) Often, in areas where there’s adequate radar coverage, the usual drill is for ATC to vector you to the localizer, at a point somewhere outside the final approach fix. Once you’ve received your approach clearance, tune in the ILS frequency, identify it, check that the marker beacon lights are working, and get ready to intercept the localizer. Like all IFR procedures, the key to shooting a good ILS begins with preparation, anticipation, and staying ahead of the airplane. Or, in the worst case, you may be tricked by false signal “lobes” that mimic inbound-path CDI indications. What does this mean? It means that if you are disoriented and outside these coverage areas, you won’t have reliable ILS signals. Closer to the runway-out to about 10 nautical miles from the runway-signals are good within 35 degrees of the course centerline. At most, reliable signals extend as far as 18 nautical miles or so, but that’s only for localizer guidance within 10 degrees of the course centerline. Localizer and glideslope signals have limited ranges. That’s well worth remembering on windy nights, or whenever visibilities are restricted by fog, rain, or other restrictions. Large crab angles of the sort needed to compensate for healthy crosswinds may require that you look to one side or the other to spot the runway.
Fly the centered needles “down the pipe,” and you’ll find the runway dead ahead, assuming a no-wind condition. The pilot-and/or the autopilot-responds to these commands by observing course deviation indicator (CDI) deflections and making small heading and pitch corrections so as to keep both localizer and glide slope needles centered. The localizer part of the ILS signal gives left-right steering commands so you can stay on the signal’s centerline the glideslope signal gives similar up and down commands. The ILS uses paired frequencies to provide an exact approach path for alignment with the runway centerline, as well as precise descent guidance along that path. Nearby terrain or obstacles can push minimums higher, for example. (Actually, the visibility is measured by runway visual range-RVR-transmissometers, which measure visibility along a portion of the runway’s length.) However, those minimums are generalities. The big value of the most common Category I ILS approach is its ability to provide both lateral and vertical guidance to runways experiencing weather as low as 200-foot ceilings and/or one-half- mile visibilities.
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