![]() ![]() If you were lucky-or wealthy-enough to have an RMI (remote magnetic indicator), which was really nothing more than that bearing pointer on a compass card that, instead of merely being fixed or manually adjustable, was slaved to your heading indicator, life got a whole lot easier. (I’m told it could be done, but I’ve never witnessed it myself.) Consequently, most of us struggled to precisely fly an NDB approach. The bearing pointer was useful for navigation, but that compass card was a challenge because the numbers on it never corresponded to your actual heading on the heading indicator unless you were really diligent at manually adjusting it. The venerable and once-ubiquitous King KR-86-when it worked-provided an ADF bearing pointer on a user-adjustable compass card. Bear with me as we explore a little instrument-flying history.) Perhaps you once learned to fly an NDB approach. ![]() We’ll start by wandering at least 20 years back down memory lane. Now, let’s look at how things work with an HSI. But, they were developed with a conventional navigation VOR/LOC indicator. Those rules are the takeaway from the previous article. If you’re inbound on the back course or outbound on the front course, the shaded part of the feather is on your left, so you correct by steering away from the CDI. If you’re inbound on the front course, or outbound on the back course, the shaded part of the feather is to your right and you correct by chasing the needle. It doesn’t matter where you’re headed or what you’re doing-if you’re on the shaded side of the feather, the CDI is to the left. If you’re off course on a localizer or a localizer back course approach, and you’re on the side of the localizer feather on the chart that has the shading or other differentiation, the course deviation indicator (CDI) will swing to the left. The OBS setting doesn’t matter to the electronics on a localizer, but this is a good rule as we’ll see a bit further down. The Rules Rule #1Īlways (always!) put the localizer inbound front course under the omni-bearing selector (OBS). There’s too much material for a proper review, so let’s just skip right to the good stuff. Boring and repetitive as that is, we needed to start there to get the basis for understanding a localizer and a localizer back course using a conventional dedicated navigation indicator (VOR/LOC) and the need to sometimes chase the CDI to correct, and sometimes to pull it. Produces two amplitude modulated antenna patterns one pattern with an audio frequency of 90 Hz and one pattern with an audio frequency of 150 Hz, one left of the runway centerline and one right of the runway centerline.In last month’s IFR Clinic we discussed how VORs work. Please see the FAA article Ground-Based Navigation - Instrument Landing System (ILS)Ĭhoose the only correct statement about the localizer beam system used by aircraft to find the centerline of a runway during an Instrument Landing System (ILS) approach to an airport. ![]() See Wikipedia's article Instrument landing system. The horizontal guidance is provided by ground transmitters of 90 Hz and 150 Hz signals, so that the airplane stays within 10° of the centerline, and must correct if within 35° of the centerline on either side.įor vertical orientation, the same ground system of is simply turned sideways, providing upper 90 Hz and lower 150 Hz signals (Glideslope Signal), so that the airplane stays within the 3° angle.įor more information well-illustrated, please see Boldmethod site, for the article How An ILS Works. "ILS uses two directional radio signals, the localizer (108 to 112 MHz frequency), which provides horizontal guidance, and the glideslope (329.15 to 335 MHz frequency) for vertical." Great explanation on a YouTube video from the FlightInsight channel, titled How ILS Works | Instrument Landing System Explained | IFR Training, 11:40 minutes (set at 1.5 speed to go faster)įrom Wikipedia's article Instrument landing system The Instrument Landing System (ILS), guides airplanes both horizontally and vertically. The question asks for the frequency RANGE. What is the frequency range of the localizer beam system used by aircraft to find the centerline of a runway during an Instrument Landing System (ILS) approach to an airport?
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