Think of the left side of the conventional VOR/LOC indicator as also being shaded so the CDI goes to the shaded side of the indicator when you’re on the shaded side of the localizer, telling you to correct to the left. The key to understanding the localizer indication is to remember that the inbound right side of the localizer front course is shaded. Pilots typically get into the most trouble with the HSI on a localizer. Some examiners might get upset if you hold using an HSI with the holding radial set instead of the inbound course, but the smart pilot will set whatever makes the IFR flying easier. Knowing this, you can, for example, fly a holding pattern with either the radial or the course set under the HSI course pointer. The course is still on 180, and the needle hasn’t changed position relative to the course pointer, but with the instrument upside-down, the needle still seems to be deflected to the left, telling you to correct to the left. To envision how the HSI works, imagine taking that VOR indicator with the course on 180 and a right needle deflection and simply turn it upside down so your 360 heading is back at the top. After a bit the CDI will be to the left, telling you to adjust your heading to the left to get back on course.īut spin the course around to 180 degrees and the CDI will flip to a right needle deflection. You’ve got a course of 360 selected and the needle is centered. You’re south of the station headed directly north to the station. But unlike the VOR that would give you reverse CDI information, the HSI will give you directionally correct CDI guidance in either case, so it doesn’t matter if the pointer is set on your course or the reciprocal of the course.Ĭonfused? Imagine you’re using a conventional VOR indicator. The HSI also provides a To/From indication that flips as you rotate the pointer. When operating with a VOR, the CDI can be centered with either the head or tail of the pointer on the correct number on the compass card, just like a VOR indicator. The rectilinear CDI moves to either side of the pointer with the CDI centered, it becomes part of the shaft of the course pointer.īut the term course pointer isn’t necessarily accurate. The HSI has a short pointer that you set to the desired course on the compass card around the outside. In this fashion, the VOR indicator’s course pointer and CDI would rotate with the heading. The answer was the horizontal situation indicator (HSI) that put a VOR/LOC indicator inside the heading indicator compass card. But relative angles of the current position remained difficult to envision, particularly with the windshield-wiper movement of the less expensive indicators versus the more intuitive rectilinear movement. This gave the pilot a separate indication of radial and the relationship to a desired course on the VOR indicator. The RMI needle points to the VOR just like an ADF pointer. Some pilots added a radio magnetic indicator, RMI. The problem with the basic VOR display is that the pilot needs a graphic mind to maintain situational awareness and it was easy to get confused sorting out course from radial from heading and position, while deciphering what the To/From flag was telling you. Add a little clever manipulation in the indicator, and you can select a specific course you want to fly to or from the station and the indicator’s course deviation indicator needle (CDI) will tell you which way to turn to get back to the selected course. To better understand the HSI, we’ll have a quick VOR review, then see how the HSI brings it all together.Ī VOR signal provides the exact angular relation of the receiver to the station. I get a lot of HSI questions-although rarely that convoluted-now that so many panel mount and portable devices contain an electronic HSI. Your HSI course points back to the runway and you’ve got a right needle deflection. You’re outbound on the localizer back course. Let’s start with an old hangar-flying puzzle.
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