#ILS LOCALIZER FREQUENCY CODE#
(Contrary to what you may have hoped, the dots and dashes could be either the letter ‘A’ or the letter ‘N’ the Morse code identifier for the letter ‘M’-as in middle-would be hard to distinguish from the three dashes for the letter ‘O’. The middle marker is usually activated as you reach decision height about a half-mile from the runway.
This would appear to you as a flashing amber beacon with alternating Morse code dots and dashes at the slightly more urgent frequency of about 190 per minute, with the audio tone at a much higher 1300 Hz or so (around an E, two octaves above middle C on the piano). You would hear (and see) the next one, the middle marker, at about 3500 feet from the runway. At most single engine approach speeds, you would hear it for perhaps 20 seconds as you flew through the signal. Assuming you remembered to turn it on, you would see a purple light on your marker beacon display, and you would also hear a repeating three-dash Morse code identifier (the letter ‘O’) at about 120 Hz (although the actual ‘continuous wave’ sound, if you are musically inclined, would be at about G above middle C, or around 400 Hz). The first one, the outer marker, is usually located just inside where the glideslope is first intercepted, which can be between 3.5 and seven miles from the runway threshold. In addition, various forms of approach lights are also part of each ILS installation.Īn ILS can have three such beacons in succession, each progressively closer to the runway, although most general aviation pilots flying under Part 91 will usually make use of ILS approaches having only the first two. These broadcast an upward-directed (but essentially non-directional) elliptical VHF signal at 75 MHz, and each provides its own unique audible as well as visual indication in the cockpit when they are being over-flown, so you have additional information to confirm where you are at that moment. (UHF generally means 300 MHz to 3 GHz.) Associated with these, each ILS installation also features so-called ‘marker beacons’ at precisely located intermediate positions along the descent path. Unlike VORs though, an ILS actually uses two signals: a VHF signal (which means anywhere between 30 to 300 MHz) for the localizer, and for the glideslope, an automatically paired and dedicated UHF frequency. Another piece of information provided by the various components of an ILS is distance remaining to the runway, as well as target altitudes at certain points along your approach path.
The vertical thickness of an ILS glideslope is but 1.4 degree, top to bottom, and the width of its horizontal component, the localizer, can be as little as three, up to about six degrees.) The runways having an ILS also must have certain unique and easily identified approach light configurations. (When I say very accurate, I should quantify that. (Of course, the PAR or precision approach radar that I wrote about last year also qualifies as a precision approach, but I’ll concentrate on the ILS here.) So what is it that makes an ILS so special?Īn ILS of course provides very accurate vertical as well as lateral guidance to the extended centerline of what are always relatively long, wide, specifically well-marked, well-lit, and well-maintained runways. Until there are many more GPS WAAS approaches besides the few now coming online, for a while yet at least, the odds are that if you have to get down through a layer of low clouds, the bases of which might be as low as 200 feet, you’ll be flying an ILS. Given a choice between the somewhat more relaxed progression of a non-precision descent profile and the relatively more rapid cross-checking required to remain within the allotted confines of a precision approach path, when the chips (and the ceilings) are down, the precision approach is definitely the better of the two. Most pilots with instrument ratings would probably agree that when it comes to an uneventful passage through haze, gloom, or dark of night and back to Mother Earth, an ILS is a much better deal than a VOR approach.
0 kommentar(er)
