Test: Which way will the CDI move? As you turn the OBS to that 90-degree difference from the received radial, both the ambiguity indicator and the CDI will reverse. Turn the OBS value counterclockwise, reducing the numbers. Now, say you start with the CDI centered and a “To” indication. Again, the concept is that if you are indeed flying toward the station on a course of 270 and drift south you want to correct by turning right.Ībove I said that if you simply turn the OBS past 90 degrees difference from the received radial, the ambiguity indicator will flip. The concept behind this assumes you’re flying away (“From”) from the station, so you’d correct to the left to get back onto the 090 course from the station.Ĭonversely, if the OBS is 270, with a “To” indication, as you drift south the CDI goes to the right. If you drift southward, the CDI will move to the left. You’re still east of the station with 090 in the OBS and a “From” indication. The CDI works with the ambiguity indicator, while both are determined by the received radial and the OBS setting. Let’s add the course deviation indicator (CDI). One implication of this is that as you turn the OBS, the ambiguity indicator will flip or reverse as you turn the OBS beyond 90 degrees difference between it and the received radial. On the other hand, with 270 in the OBS, you’ll get a “To” indication, saying you’re in a position that’s 270 degrees (or, between 180 clockwise to 360 degrees) to the station. In fact, if you put 090 in the OBS, you’ll get a “From” indication if the received radial is in the same hemisphere, from 360 clockwise to 180. With a “From” indication, you’re 090 degrees from the station. Say you’re east of the station with 090 in the OBS. If the OBS matches the radial received from the station, the ambiguity indicator will say, “From.” Your actual heading is irrelevant. The magic happens as the received radial is combined with a selected radial (omni-bearing selector, OBS) to determine a to-from indication (ambiguity indication) and a left-right course correction.
The station broadcasts a VHF signal from which the receiver can tell its direction (radial) from the station. Similarly, an observer northwest will see “315.” Thus, a person east of the lighthouse will see “090” in the center of the beam as it sweeps past. Say the beam from the lighthouse has the direction embedded in it. Let’s start by thinking of a VOR as a lighthouse whose light sweeps the horizon.
LOCALIZER SYMBOL SERIES
I’m going to use a series of technologically inaccurate, but conceptually useful examples. Localizers first require an understanding of VORs, old school or not. As a newbie, I flew with a seasoned ATP who nearly flew us into a mountain because he misunderstood this stuff.) VOR Basics (Oh, and you’re not alone in being confused.
However, if like most pilots, the setup for these approaches makes you at least think-or worse, look for an alternative-this is for you.
LOCALIZER SYMBOL HOW TO
If you know right away how to set up your navigation, what OBS settings to use and how to read your instruments (HSI or VOR/LOC indicator) on the approach with procedure turn and missed, you can stop here and even skip next month’s clinic. Look at the Grand Forks LOC BC Runway 17R approach. You shouldn’t entirely dismiss VHF navigation just yet. But, there are still a lot of localizer and localizer back course approaches out there, and you may have to fly one. Some of you are already yawning, thinking to yourselves, “With GPS and moving maps, who needs VHF nav anyway?” To an extent, that’s a valid argument, especially regarding VORs.
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