Horizontal Situation Indicator Explained | HSI Test Questions | How an HSI Works | Chase the Needle

this is the story of when two instruments the directional gyro and the vor receiver met up and became close creating a single new instrument called the horizontal situation indicator or hsi the hsi is a combination of these two instruments allowing you to have heading and navigational information in one place making your instrument scan easier the instrument itself is a bit more complicated at first and the knowledge test has some of its toughest questions related to this instrument we'll break down those challenging questions in a bit but first let's learn about how this instrument works first of all this is still your standard run-of-the-mill directional gyro here we are on a 2-3-0 heading if we turn right or left the hsi responds accordingly just like the directional gyro does nothing fancy since the hsi also combines the vor function let's take a look at how that works we're on that two three zero heading flying along this airway the zero five zero radial inbound towards the vor if we start to move to the right of the airway the green needle deflects to the left just like a vor receiver would this needle is the cdi it'll deflect the opposite way as we move to the other side of the airway also just like a vor we can select a desired course with the obs function we can twist that knob at the bottom left and the green core selector will move from two three zero to two four zero we've now selected a two four zero course inbound to the vor since we're not on that course the needle will deviate off center too when we twist back to the inbound course we're actually flying the two three zero the needle will center up again notice the core selector has a green head with an arrow that points to the selected course and a green tail with no arrow that is the reciprocal of the selected course so that's the full functionality of the hsi let's have an example using all of them let's say we're up here north of the airway headed west we'd like to get back on that airway and track it inbound towards the station the airway is the zero five zero radial we don't wanna fly that heading as it would be flying away from the station but instead we want that to be the reciprocal of our heading so we'll twist the knob so that the tail is on that zero five zero and the head with the arrow is pointed at two three zero now the indication that we get is that the cdi or needle is to the left of center remember from vors that we need to chase the needle so we'll turn left too but what heading should we turn to if we turn to our desired course of 230 we'll look like this sure we've chased the needle by turning left but all we'll do now is fly parallel to the airway we won't rejoin it the needle will stay to the left of center and we'll never actually pass over the vor station no we'll need to turn more to the left we'll use a heading of 185 now notice the indication of the hsi the needle is to the left our heading is pointing us in a direction such that the white lubber line is pointing at the needle we're literally chasing the needle now this is the great visualization that the hsi gives us we can see our intercept happening here so as we fly this heading and approach the airway the cdi needle will swing towards center indicating that we've reached it at this point we can turn our 230 heading inbound towards the station everything is nicely centered up and we just need to keep it centered as we proceed in now we'll get closer to the vor since we're flying to the station that white triangle is pointed the same direction as our green arrow which just like in a vor is the two indication when we fly over the station this triangle will flip from 2 to from notice how the white triangle is pointed the opposite direction from the green arrow now ok we were promised some knowledge test questions on the hsi so here they are the test will give you a vor station with four radials splitting the area into quadrants like this then you'll get an hsi with given indications let's say we're looking at this hsi here we need to identify the direction the aircraft is pointed and where it is in relation to the vor let's start with the easy part the aircraft's heading we can read this right off the top under the lubber line as 205 degrees so the aircraft will be oriented like this now we don't know yet where this aircraft is in relation to the station notice the green course selector arrow it's pointed at 0 9 0. also notice the white triangle pointed the same direction as the green arrow marking the two indication what the instrument is set up to do is have us fly inbound to the station on a zero nine zero heading if we were to do this fly inbound to the station on the zero nine zero heading it would put us on this radial right here however if this is where we were located the needle would be centered but it's not it's deviated to the right this means that in order to get on that line we'd need to chase the needle to the right since that's the case we must be up here above the line left of course let's check our work by actually correcting course first we'll chase the needle by flying a heading to intercept this 135 heading here has us chasing the needle notice the lubber line pointing straight towards the deflected needle now we'll hold that heading until the needle centers then turn to our inbound heading of zero nine zero and everything's centered up let's try another one we'll start with the easy part aircraft heading it's 135 degrees now we need to figure out where this aircraft is located in relation to the station the course selected is 270 degrees this time though notice the white triangle pointed to the opposite direction from the green arrow this is the from indication this means that our desired course is to fly outbound from the station along the 270 radial if the needle was centered this is what our position would be however the needle is right of center if we want to fly on that radial we'll need to correct to the right where would the aircraft need to be such that a correction to the right would put us outbound on the 270 radial it would need to be down here below the radial let's check our work again in order to chase the needle from the one three five heading we'll need to turn all the way around now our lumbar line is aimed straight at that green cdi needle we can fly this heading until the needle centers then turn to our outbound heading of 270 notice everything is centered up and the green arrow and white triangle are pointed in opposite directions which is the from indication we'll look at some other hard test questions in a bit but right now let's examine one more function of the hsi on a precision approach like this ils here we're able to use the green cdi needle as our localizer but we're also able to get a glide slope indication here we are approaching the course initially if our hsi is tuned to the localizer frequency we won't get any indication until we get closer so notice the red off flag what happens when we approach though is that the hsi will come alive the red flag goes away the green needle deflects to the left since the approach course is still to our left and those two yellow glide slope indicators appear on the top next to the gs for glideslope these work just like the glide slope needle on a vor receiver at first as we approach the glide slope from below the indicator will be above center as we intercept the glide slope the indicator will fall towards center if we start to get too high and pass above the glide slope the indicators will fall below center as we correct the indicators will correct to center we can fly this ils approach with a really limited amount of scanning this is the real advantage to the hsi now let's get into some of the trickier knowledge test questions which are based on localizers the test starts by showing you runway 927 then it gives you a localizer feather like this one these two football symbols are marker beacons this is the localizer course we know it's the localizer chorus because of two telltales first the shading in the feather is on the right side second because of the presence of those marker beacons a localizer course uses normal sensing where we'll chase the needle which is what we've been used to up to now as we know in normal sensing if we deviate left of course the needle swings right and if we go right of course the needle swings left we need to chase the needle to get back on course here's where it gets tricky the test will also show you this feather symbol this is a back course and works differently than the localizer we know it's a back course because the shading is on the left side of the feather and there's no marker beacons a back course uses reverse sensing where the motto is pull the needle let's go over to that side and see how it works this time if we deviate to the right of course the needle swings to the right and if we're left of course the needle swings left in order to get back on course we don't chase the needle but we pull the needle meaning in this case we need to fly to the right to get back on course this gets really confusing on the test so here's an important rule of thumb both for the test and for real world flying no matter what if the aircraft is on the shaded side of the feather the needle will be off to the left as it is here in both depictions okay let's get into some examples we have this indication first we'll start with a simple step of figuring out aircraft heading it's due north in this case but where are we in relation to the runway the green core selector is set to 270 which means our intention is to fly inbound to runway 27 which means we're flying the localizer course since the needle is centered we're perfectly on course which puts our aircraft here we need a dramatic course correction to stay on the localizer but for now anyways we're dead center notice though that in addition to this position the aircraft could also be on the other side of the runway over here just because we've selected 270 to fly inbound to runway 2-7 doesn't mean we haven't for example flown past it to the other side of the runway in that case we'd still have the same hsi indication depicted here the test will often ask you to identify two aircraft positions in this way okay let's try another here we start with our aircraft heading of zero nine zero we just have to figure out where the plane is we've selected course of zero nine zero which is the test maker's way of saying we intend to fly inbound to runway nine this means we'd be flying the back course if the needle were centered we'd be perfectly in the middle of the feather here inbound to runway nine the needle is deflected right though we need to pull the needle on the back course so in order to rejoin the course we'd need to fly to the left this means we must be down here right of course also note that we might be on the opposite side of the runway like this over here how about one more for good measure our aircraft is on a 3-1-0 heading where is it located though we intend to fly the back course as indicated by the selection of course zero nine zero if we were centered up on the back course the needle would be centered but it's not it's off to the right we need to pull the needle by flying left in order to get back on center so we're down here again right of course and again note that we could also be on the other side of the runway like this with a given indication okay so that's a rundown of the hsi a lot of us don't get a chance to use these in flight much as instrument students but as you move up to more advanced avionics you'll see these more and more because of their natural advantages in improving the instrument scan take some time to practice with it and it'll make your job of tracking and intercepting a course less of a chore if this was helpful please click subscribe so that you could stay up to date on every new training video coming out each tuesday and 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Channel: FlightInsight

Views: 331,471

Keywords: Horizontal Situation Indicator Explained, HSI Test Questions, How an HSI works, Lubber Line, OBS, CDI, Directional Gyro, HSI, Horizontal Situation Indicator, Airway, VOR, IFR navigation, IFR training, chase the needle, horizontal situation indicator function, pull the tail, push the head pull the tail

Id: p9FHfzJFnQk

Length: 12min 30sec (750 seconds)

Published: Fri Sep 03 2021