Back-course on an HSI

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CerroTorre

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CerroTorre
OK, this keeps hanging me up and I can't play around on my simulator to verify right now...so...

This references IFR exam questions regarding position correlating with an HSI on an ILS:

When flying an ILS, with the correct course selected (recognizing it has no effect on the needle movement), if you overfly the MAP and are effectively flying "up" the BC, will the needle show reverse sensing (this being the one time an HSI will show reversed relationship to the course)?

And therefore, when flying a BC approach, you should select the BC with your CDI to make sure it displays correctly?

Not sure why this one makes my head turn in circles...but it does...

Thanks all.

edit to add:
Also, recognizing that I haven't seen missed approach procedures that tell you to fly the BC initially. Although I'd guess they exist. I can think of one (KASE LOC/DME-E) that has you intercepting a BC, but that's different of course. In that case, would you select 123deg on the CDI and just fly to the tail with normal sensing?

Thanks again.
 
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The easiest way on a written test is that the needle will deflect to the left (with respect to the arrowhead) on the shaded* (right) side of the localizer and vice versa.

*Except some ignorant graphic artist at the FAA reversed the shaded and unshaded sides on the drawings in the knowledge test supplement. The shaded side is supposed to be on the right side of the front course.

If you fly a localizer approach past the airport and keep going no, you do not have reverse sensing. Reverse sensing with a localizer occurs when the aircraft heading is 180° from the front course. HSI solves this by allowing you to set the needle "upside down", i.e. to the front course, during a backcourse approach.
 
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Always point the HSI needle towards the front course.

I’m a little confused about your “flying up the BC” terminology, but if you fly a localizer front course (say, a 090 course with the head of the needle on 090) past the airport, a needle deflection towards “N” on your HSI means you’re south of course, with the CDI deflected to the left. If you then turn around and fly the BC westbound towards the airport with the head of the needle still at 090, a needle deflection towards “N” still means you’re south of course, and since you are pointed towards the tail of the needle, it’s now a right correction, but still towards the CDI needle.

take a piece of paper, draw a compass rose and course needle, pretend the sofa is the runway, and walk around it for a bit. Keep the compass rose properly oriented whichever way you’re walking, and use a pencil to move back and forth as your CDI needle.
 
OK, sorry if I'm being incredibly dense...but here's the issue: In "G" the HSI is set to the front course, position 11 is past the MAP and on runway heading, and is indicating that the course is to the left. Seems like it is indicating correctly and in accordance with your description. The FAA says "I" is the correct answer where the BC is (incorrectly) selected and we are showing reverse sensing...

edit: as noted above, we're supposed to ignore the stupid mis-coloring of the FC feathers.

Question.png HSIs.png
 
It's Sheppard Air. But is it possible that BOTH "G" and "I" are, in a sense "correct". Would an HSI that is set incorrectly to the BC display as in "I" as well? The aircraft is flying backwards "up" the BC but with it set to the BC (which would be (?) correct if we WERE flying the BC...on the appropriate heading of 090...?).

:: facepalm ::

Again, apologies if I'm being dense here.
 
CerroTorre said:
OK, sorry if I'm being incredibly dense...but here's the issue: In "G" the HSI is set to the front course, position 11 is past the MAP and on runway heading, and is indicating that the course is to the left. Seems like it is indicating correctly and in accordance with your description. The FAA says "I" is the correct answer where the BC is (incorrectly) selected and we are showing reverse sensing...

edit: as noted above, we're supposed to ignore the stupid mis-coloring of the FC feathers.

View attachment 98383 View attachment 98384
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Ignore my earlier post if you saw it before I deleted it.

G and I are equivalent, just with different courses selected. If that question is scoring G as an incorrect answer then it's wrongly scoring the question. If G is not one of the choices available to you in the question then I is correct.
 
To the north of this course line (on the non-shaded side) is always going to indicate deflection to the right with reference to the head of the needle. There does not appear to be a correct HSI selection available.
 
MauleSkinner said:
To the north of this course line (on the non-shaded side) is always going to indicate deflection to the right with reference to the head of the needle. There does not appear to be a correct HSI selection available.
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The shading is reversed. The front course in the diagram is the one with the marker beacons.
 
Thank you dmspilot. That aligns with how I'm seeing it. G or I would both be a possible HSI display for position 11.

That said, no fault of Sheppard Air. I'm still getting used to their approach and am on the "Step 1" process and just realized G may be excluded when viewing the full question. My brain has a hard time turning off the option to look at the full figure when determining a correct answer.

Regardless, thanks for clarifying for me. That all makes sense.
 
dmspilot said:
The shading is reversed. The front course in the diagram is the one with the marker beacons.
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Well, that being the case, I’d agree that since G and I are equivalent, there is no correct answer, but G would be the “most right”, since the needle is pointed the wrong way in I.

Somebody at Sheppard is an idiot, too, apparently.

If the questions are that bad, I would suggest the OP ignore localizer-based HSI questions.
 
CerroTorre said:
OK, this keeps hanging me up and I can't play around on my simulator to verify right now...so...

This references IFR exam questions regarding position correlating with an HSI on an ILS:

When flying an ILS, with the correct course selected (recognizing it has no effect on the needle movement), if you overfly the MAP and are effectively flying "up" the BC, will the needle show reverse sensing (this being the one time an HSI will show reversed relationship to the course)?

And therefore, when flying a BC approach, you should select the BC with your CDI to make sure it displays correctly?

Not sure why this one makes my head turn in circles...but it does...

Thanks all.

edit to add:
Also, recognizing that I haven't seen missed approach procedures that tell you to fly the BC initially. Although I'd guess they exist. I can think of one (KASE LOC/DME-E) that has you intercepting a BC, but that's different of course. In that case, would you select 123deg on the CDI and just fly to the tail with normal sensing?

Thanks again.
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When you say “...And therefore, when flying a BC approach, you should select the BC with your CDI to make sure it displays correctly?” keep in mind that not all CDI’s are going to have a BC selection on them. If you are flying inbound on a Back Course, reverse sensing is ‘correct.’ If you flying out bound on a Front Course, reverse sensing is ‘correct.’ Now if you have a CDI with the BC gizmo and you select it, you will get normal sensing when flying inbound on a Back Course, or outbound on a Front Course. I think
 
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MauleSkinner - to be clear, Sheppard Air's material is correct. My larger questions about proper HSI indications are what I'm working to clarify now. The way Sheppard Air's course is designed is that as you move through the questions in their "Step 1", it blocks you from seeing the incorrect answers, which prevents you from seeing the answers the FAA is not including in the answer options. If you forget that critical part, and you're me, it's easy to confuse yourself looking at the wrong information. =)

In this question, after review, "G" is not included in the FAA answers despite the fact that it is displayed in their associated figure. I hope that's clear.

Short answer is Sheppard's system is not at fault here.

But thanks all for the conversation. It's making sense.
 
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luvflyin - so I think you're saying that applies even on an HSI. Fly a BC Approach with the CDI set to the front course and expect reverse sensing.

This will likely be fully clarified as soon as I either play around on the sim or next go up with a CFI if I can get a plane with a G5 HSI. Currently training with old school Nav1 ILS, Nav 2 VOR and a 430W.
 
CerroTorre said:
MauleSkinner - to be clear, Sheppard Air's material is correct. My larger questions about proper HSI indications are what I'm working to clarify now. The way Sheppard Air's course is designed is that as you move through the questions in their "Step 1", it blocks you from seeing the incorrect answers, which prevents you from seeing the answers the FAA is not including in the answer options. If you forget that critical part, and you're me, it's easy to confuse yourself looking at the wrong information. =)

In this question, after review, "G" is not included in the FAA answers despite the fact that it is displayed in their associated figure. I hope that's clear.

Short answer is Sheppard's system is not at fault here.

But thanks all for the conversation. It's making sense.
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Either way, you’re wasting time trying to make sense of it with something that doesn’t have a correct answer.
 
MauleSkinner said:
Either way, you’re wasting time trying to make sense of it with something that doesn’t have a correct answer.
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I and G are both correct. Having two correct answers isn't the same as not having any.
 
CerroTorre said:
OK, sorry if I'm being incredibly dense...but here's the issue: In "G" the HSI is set to the front course, position 11 is past the MAP and on runway heading, and is indicating that the course is to the left. Seems like it is indicating correctly and in accordance with your description. The FAA says "I" is the correct answer where the BC is (incorrectly) selected and we are showing reverse sensing...

edit: as noted above, we're supposed to ignore the stupid mis-coloring of the FC feathers.

View attachment 98383 View attachment 98384
Click to expand...
Here's how I'd handle this: EDIT: Disregard this post. I didn't see the MM in the diagram, so this is all wrong. :oops:
  • Rule out "H" because the headings don't match.
  • Assume the drawing is accurate and there's a fan marker on the back course.
  • The correct course would be 090°, so "I" is set up correctly and "G" is set up in reverse (hint).
  • If you are at position #11 and trying to find the centerline you'd steer away from the needle, since it's set up in reverse of normal, but that would take you farther from the centerline based on the indication, so rule out "G".
  • "I", being set up correctly, is saying "Steer right" to get on the centerline, which would be correct if you were pointed the opposite way of #11. But you aren't. You're going the opposite way of the course, so you have to steer away from the needle when you do that (think back course approach), so "I" corresponds with reality and is the answer.
 
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dtuuri said:
Here's how I'd handle this:
  • Rule out "H" because the headings don't match.
  • Assume the drawing is accurate and there's a fan marker on the back course.
  • The correct course would be 090°, so "I" is set up correctly and "G" is set up in reverse (hint).
  • If you are at position #11 and trying to find the centerline you'd steer away from the needle, since it's set up in reverse of normal, but that would take you farther from the centerline based on the indication, so rule out "G".
  • "I", being set up correctly, is saying "Steer right" to get on the centerline, which would be correct if you were pointed the opposite way of #11. But you aren't. You're going the opposite way of the course, so you have to steer away from the needle when you do that (think back course approach), so "I" corresponds with reality and is the answer.
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I’m just saying that if you have to manufacture conditions that make an answer correct, it’s a negative learning scenario.
 
dtuuri said:
Here's how I'd handle this:
  • Rule out "H" because the headings don't match.
  • Assume the drawing is accurate and there's a fan marker on the back course.
  • The correct course would be 090°, so "I" is set up correctly and "G" is set up in reverse (hint).
  • If you are at position #11 and trying to find the centerline you'd steer away from the needle, since it's set up in reverse of normal, but that would take you farther from the centerline based on the indication, so rule out "G".
  • "I", being set up correctly, is saying "Steer right" to get on the centerline, which would be correct if you were pointed the opposite way of #11. But you aren't. You're going the opposite way of the course, so you have to steer away from the needle when you do that (think back course approach), so "I" corresponds with reality and is the answer.
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I and G are identical, your technique doesn't work.
 
dmspilot said:
I and G are identical, your technique doesn't work.
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MauleSkinner said:
What I’m seeing is either you have to say the shaded side is wrong, or the CDI deflections are wrong.
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I don't see either of your points, but I do now see a MM which was dwarfed by the OM and so I took it as a Fan Marker. In that case I say either the shading is wrong or the MM is wrong. My "technique is based on an ILS 9.
 
dtuuri said:
I don't see either of your points, but I do now see a MM which was dwarfed by the OM and so I took it as a Fan Marker. In that case I say either the shading is wrong or the MM is wrong. My "technique is based on an ILS 9.
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if 090 is the front course, the CDI in position 11 would be to the right with respect to the head of the needle, regardless of course setting or airplane orientation. All 3 needle deflections are to the left.
 
CerroTorre said:
luvflyin - so I think you're saying that applies even on an HSI. Fly a BC Approach with the CDI set to the front course and expect reverse sensing.

This will likely be fully clarified as soon as I either play around on the sim or next go up with a CFI if I can get a plane with a G5 HSI. Currently training with old school Nav1 ILS, Nav 2 VOR and a 430W.
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Yeah, I was replying to your CDI paragraph. I hadn’t read beyond your first post when I replied and hadn’t seen the HSI test question pictures yet. But while were here, I have a question. When you said “set to the BC” did you mean a CDI or HSI that has a BC function? A button you push so that it will give you normal ‘sensing’ when flying a Back Course Approach? Or did you mean something else?
 
dtuuri said:
I don't see either of your points, but I do now see a MM which was dwarfed by the OM and so I took it as a Fan Marker. In that case I say either the shading is wrong or the MM is wrong. My "technique is based on an ILS 9.
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My point is "I and G are identical, your technique doesn't work." I don't know how else to say it.

MauleSkinner said:
if 090 is the front course, the CDI in position 11 would be to the right with respect to the head of the needle, regardless of course setting or airplane orientation. All 3 needle deflections are to the left.
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The front course is 270 according to a previous edition of the figure.

96_figure96.gif
 
What's funny about all this is that it all revolves around what I'm coming to realize is a FAA testing system that is just hilariously bad at times. I have lost count of the times I have run across questions/answers that are just plain wrong (this is actually one of the LESS confusing/wrong ones - the feather colors/shading issue). Over and over the explanation of a question is something like (to paraphrase) "so, the ACTUAL answer to this question is X, but the FAA testing computers grade Y as correct. So you should just memorize answer X as the correct answer and forget about the real world answer."

It's beyond infuriating and at times just hilarious. And a significant source of stress as I'm prepping.
 
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MauleSkinner said:
Why? Apparently it’s acceptable to reference a diagram that’s not shown.
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Why not? I told you the source of the error and who to contact to correct it. Oh I see, it's because writing cryptic arguments against everything I write is the more productive strategy, obviously. :rolleyes:
 
dmspilot said:
Why not? I told you the source of the error and who to contact to correct it. Oh I see, it's because writing cryptic arguments against everything I write is the more productive strategy, obviously. :rolleyes:
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What’s cryptic about my arguments?
 
To rabbit trail a little, on the issue of FAA exam weirdness:

One example would be an ETA calculation question. It's a math question - so (you'd think) there should be one single precise answer (although we all know real world always includes some fudge factor). But still, none of the available answer options match that calculated, correct answer. You have to pick the one that falls closest to the actually correct ETA.

Others are holding pattern entries when entering on the precise dividing bearing between between parallel and teardrop. Hierarchy would direct you to choose teardrop over parallel ... but the FAA only grades parallel as correct. If you choose according to guidelines you get it graded wrong. :: facepalm ::

I could go on.

One note: looks like I'm unable to locate said "hierarchy" in the AIM or 8083 manuals. That comes from a written explanation. Still doesn't change the problem with determining the "correct" FAA answer... Oh well, live with it. =)
 
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MauleSkinner said:
Specific courses, needle deflections, etc.
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You have spent more time arguing over semantics about whether it's the question that's wrong or if it's the answers, when it is clear where the error originated.
 
dmspilot said:
You have spent more time arguing over semantics about whether it's the question that's wrong or if it's the answers, when it is clear where the error originated.
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No, I was arguing that one of them has to be wrong. I made no arguments about which was wrong.
 
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