HSI question

SixPapaCharlie

SixPapaCharlie

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My brain is fried... The answer is 11 but I am not sure why at this moment in time.


Seems to me you always fly to the line on an HSI.
Image 1 is form the practice test. Image 2 is me setting up the same scenario in an HSI simulator.
The simulated one is what I would expect to see. Why do they not agree?


testQ.JPG


hsi.JPG
 
It has something to do with the fact that it's a localizer and not a VOR, I think.
 
Because 12 and 4 are obviously wrong :).... also. backcourse(reverse sensing) with arrow pointing back to station(LOC)

Edit: not "reveverse course", "backcourse"... "reverse sensing"
 
See my post about how I got the Aspen HSI to show reverse sensing with the SL-30 but not the 430w.

Then your brain will be really fried.

tl:dnr 11 is better than 10
 
To my understanding you are on the back course of an ILS and will get reverse sensing. ILS doesn't act like a VOR.
 
Yup... Direction of the pointer only matters when it's a localizer. It has not bearing other than personal reference for VORs.

Think of it like this.. "always dial the pointer to the inbound of the front course", and you will never have reverse sensing.
 
Yeah, but I hated these questions, because it's an HSI.

There is no such thing as reverse sensing. Period. But the illusion that there is should also go away with an HSI, right?
 
The heading is 270...the CDI says you are on the shaded side of the localizer. That's numbers 7 & 11, and 11 is the only answer that matches, so ...apparently the HSI has not been set to an appropriate course.
 
There is several correct numbers, but when you look at the possible answers there H's only one that is off course... makes it easy.
 
But.... With all that said, I don't see how 11 is correct.
 
4, 7, and 11 are the only ones with a heading of 270°. So that narrows it down quickly, obviously it's not 4 since the needle isn't centered. 7 isn't correct because the needle is pointed away from the localizer which would put your airplane on the other side of the bar.
 
Grum.Man said:
4, 7, and 11 are the only ones with a heading of 270°. So that narrows it down quickly
Click to expand...

Yeah, i get that and the answer is very simple due to that fact but I need to understand the whole picture.
 
The top HSI is set up to fly east. The localizer is westbound. (There's a little teeny arrowhead at the bottom there in case you can't see it, where the awful printing mixes the arrow with the 9. Can you see that?)

Remember when you're flying a localizer on a traditional OBS, twisting the OBS knob does absolutely nothing. This is the critical piece of information they're testing and they do it poorly in the diagram because they "tell" you it's an ILS only by the diagram symbols. (I love the outer and middle marker being depicted when most of those have been decommissioned, right? So much for people converting what they learn to the real world, haha. Anyway...)

On an ILS, your OBSs becomes a simple left/right indicator and that's based on whether you're left or right of the desired flight path (and radio beam).

With an HSI, by setting it up backward, you're literally turning that entire OBS upside down and trying to read it that way. That HSI is set up upside down.

So for these goofy questions where FAA wants you to figure out that you've set the thing up backward, I just do this... either mentally or physically (since they give you a paper book with these figures) turn the head of the arrow on the HSI to line up with the ILS picture on the page. (Don't rotate the knob mentally, rotate the entire instrument.)

If you point that arrow head left along the 27 ILS, you'll see it's telling you to fly left.

Now process of elimination. 12 is centered on the localizer so it's not right. 4 is also. So the only remaining answer that works is 11. (And also 7 if it were an option.)

Technically process of elimination on this one makes it super easy without ANY mental gymnastics or even completely understanding the HSI at all. There's two airplanes centered on the localizer and one that isn't, and the needle isn't in the center. Question over, mark 11 and move on. Test taking skill vs understanding it will work on this particular question.

But I know you're trying to understand it better, thus the longer description for ya.
 
Notice that the shaded side of the feathered arrow is on the same side for both the front and back courses...if the needle is deflected to what we normally consider a "fly left" indication (which it is in the diagram), you are on the shaded side of the localizer...regardless of heading, HSI orientation, phase of the moon, whatever. If you think of it as "shaded or unshaded" rather than "left or right" or "normal sensing or reverse sensing", it's pretty easy.

Back in the good ol' days, CDIs had a dark bar on one side and a lighter bar on the other side to indicate that.
 
Honestly, as long as i pass, I will be happy because the test costs money and I don't want to take it twice.
But I don't like things where I cannot mentally trace a path to the right answer.

Simple example:
cloud clearance is higher above 10k feet. I can memorize that and the numbers.
But it helps if I can go "Well it makes sense because the speed limit is higher up there and thus the closure rate is faster so naturally blah blah blah...

With all of these questions, I am more concerned with the "why" vs. the right answer.
 
"Most correct answer"
 
SixPapaCharlie said:
Honestly, as long as i pass, I will be happy because the test costs money and I don't want to take it twice.
But I don't like things where I cannot mentally trace a path to the right answer.

Simple example:
cloud clearance is higher above 10k feet. I can memorize that and the numbers.
But it helps if I can go "Well it makes sense because the speed limit is higher up there and thus the closure rate is faster so naturally blah blah blah...

With all of these questions, I am more concerned with the "why" vs. the right answer.
Click to expand...

Basically, the HSI rotates a traditional CDI to the selected heading. For a VOR, that's the right thing. But for a localizer, the selected heading doesn't affect a CDI display, but the HSI rotates it anyway.

It sucks when you get this backwards when flying a backcourse. Of course, IRL, you pretty quickly realize that the needle reacts backwards from what you expect, and you can mentally note "reverse sensing" and then go on. But you'll have to disengage the autopilot, 'cause it will turn away from the selected course.
 
SixPapaCharlie said:
With all of these questions, I am more concerned with the "why" vs. the right answer.
Click to expand...

Nothing wrong with that!

The feathered arrow with shading is the indication it's a localizer. A localizer is an incredibly dumb device. It sends out a radio signal that allows the receiver to determine only whether it is on the localizer, left of the localizer or right of the localizer (and how many degrees).

In that diagram,
Everything on the grey shaded side will show left. Everything on the white shaded side will show right.
It's too dumb to show anything else.

You can spin the OBS knob on a traditional Instrument and the needle will not move on an ILS localizer. (Neither will the glideslope needle.)

You're essentially "undoing" all you've learned about an OBS from VOR work when you're learning to fly an ILS. Ironically this Instrument is one of the biggest breakers of the rule of primacy in the cockpit. You learned that rotating the OBS selects a radial of the VOR. Your brain wants to apply that information to the ILS and it doesn't apply anymore.

It's way easier to show this on a real HSI in flight. Especially a mechanical one and not an electronically depicted one.

Put someone on the localizer and then tell them to spin the OBS and observe the needle. It'll rotate angularly around but the center of the needle will stay centered in the middle of the instrument right on the center dot.

Because all they're doing is rotating the ILS Instrument around in circles inside their DG. Literally on a mechanical one.

If they were flying an ILS with glideslope, both needles just spin around.

The "plus" shape would just rotate around as they spin the OBS.

The needles that make up the plus don't care at all about the OBS being rotated when flying a localizer and a glideslope. They just "care" about showing where the aircraft is in relation to the two radio "beams".

The drawings and electronic versions make this relationship of how original HSIs were created hard to see. It's just one Instrument stuffed in the center of another Instrument.

Helpful?
 
Kritchlow said:
Don't see it... unless it's tuned to 27. If they are playing tricks with the shading than I'm guilty.
Click to expand...
If you were flying either the front course or back course, where would you set the HSI course needle?

If you turned the needle to that course, the deflection would remain the same, and it would probably unconfuse the issue.
 
MauleSkinner said:
If you were flying either the front course or back course, where would you set the HSI course needle?

If you turned the needle to that course, the deflection would remain the same, and it would probably unconfuse the issue.
Click to expand...
But 11 is on the left side of the course.
Heading should be irrelevant.
Lock your screen and rotate it 180°
 
mtuomi said:
...and what did the shaded areas in LOC symbol mean...?
Click to expand...
Well, to be honest I don't recall which side is supposed to be shaded. I also know it's a bit different for a BC. Thus my admission if that was the reasoning than I am guilty.
 
Kritchlow said:
Well, to be honest I don't recall which side is supposed to be shaded. I also know it's a bit different for a BC. Thus my admission if that was the reasoning than I am guilty.
Click to expand...

The left side is shaded, so it is backcourse.
 
mtuomi said:
The left side is shaded, so it is backcourse.
Click to expand...
And that is exactly why I made the disclaimer. I just couldn't remember which.

Thanks for clearing that up.
 
Kritchlow said:
And that is exactly why I made the disclaimer. I just couldn't remember which.

Thanks for clearing that up.
Click to expand...

Yep, that is the key to understand any question related to that diagram (and you'll likely get at least 2 or 3...)
 
mtuomi said:
Yep, that is the key to understand any question related to that diagram (and you'll likely get at least 2 or 3...)
Click to expand...
Shucks not me... I took that test about 33 years ago!!

It is a silly question IMO.. it doesn't test HSI knowledge, but rather knowledge in which side of the marking is shaded. That, IMO, is nonsense seeing as though you will have a chart in front of you specifying a ILS or BC.

But, that's the way it is.....
 
MauleSkinner said:
Notice that the shaded side of the feathered arrow is on the same side for both the front and back courses...if the needle is deflected to what we normally consider a "fly left" indication (which it is in the diagram), you are on the shaded side of the localizer...regardless of heading, HSI orientation, phase of the moon, whatever. If you think of it as "shaded or unshaded" rather than "left or right" or "normal sensing or reverse sensing", it's pretty easy.

Back in the good ol' days, CDIs had a dark bar on one side and a lighter bar on the other side to indicate that.
Click to expand...

Yes, right side of the localizer is always shaded. Some of us still remember the blue and yellow CDIs. (can't find a picture on Google now, booooo)
instrument_landing_system_afm_51-37_figure_16-2.png


Br-y-an, once you fly IFR enough and see enough ILS plates, you'll get used to the right side being shaded.

Of course it doesn't help that this FAA question is given without context (meant to confuse you). If they told you: "you're tuned into the ILS27 localizer", you'd know which way the deflection goes. Here, you gotta infer it from the shading.



mtuomi said:
The left side is shaded, so it is backcourse.
Click to expand...
Careful. What left side? He's flying west so it's the right side that's shaded.
 
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