how does hsi indicate back course sensing

Full Answer

Can you have reverse sensing on an HSI?

Taking this theory to the HSI where the currently flown heading is always on the top half and you can never have reverse sensing. It is also proper technique to set in the front course when flying a LOC/BC approach. This will negate the effects of reverse sensing for HSIs.

What information can be displayed on the HSI?

The HSI may display bearing and distance to a navigation aid, magnetic heading, track/ track deviation and course/course deviation.

Why is the HSI so hard to understand?

The HSI can admittedly be confusing at first because there is a lot of information packed into that one instrument. Not to mention there are two different input knobs on it (versus a VOR with just one).

Should you use a back-course approach when flying behind a HSI?

Right up front, it’s important to acknowledge that pilots flying behind HSIs have an advantage on back-course approaches. All the old analog HSIs and the current crop of digital, glass-panel-equipped airplanes, whether Garmin, Avidyne, Aspen, Sandel or some other manufacturer, have made BC approaches less of a problem.

What is horizontal situation indicator?

The horizontal situation indicator is a rather busy instrument, displaying lots of useful information. For our purposes, just as an RMI combines a bearing pointer with a heading indicator, let’s think of the HSI as a single instrument that combines a gyro heading indicator with a VOR/LOC navigation instrument. Let’s look at one of many reasons that depiction is meaningful.

What happens if Frank Bowlin flies without a Hsi?

Frank Bowlin is now so used to the brainless setup of the HSI, that if he flies without one he still has to go through the rules to stay away from that mountain.

How to determine inbound front course on AIS chart?

On AIS charts it still takes a little mental energy to determine exactly what the inbound front course is. But, if you remember Rule #2, it’s easy. Just orient yourself on the chart so you’re centered on the localizer and the charted feather shading is on your right. What’s your heading? That’s the inbound front course that you set in the OBS on your HSI.

What side is the CDI on a localizer?

If you’re off course on a localizer or a localizer back course approach, and you’re on the side of the localizer feather on the chart that has the shading or other differentiation, the course deviation indicator (CDI) will swing to the left. It doesn’t matter where you’re headed or what you’re doing—if you’re on the shaded side of the feather, the CDI is to the left. Period.

What is RMI on a compass?

If you were lucky—or wealthy—enough to have an RMI (remote magnetic indicator), which was really nothing more than that bearing pointer on a compass card that, instead of merely being fixed or manually adjustable, was slaved to your heading indicator, life got a whole lot easier.

What is a KR-86 bearing pointer?

The venerable and once-ubiquitous King KR-86—when it worked—provided an ADF bearing pointer on a user-adjustable compass card. The bearing pointer was useful for navigation, but that compass card was a challenge because the numbers on it never corresponded to your actual heading on the heading indicator unless you were really diligent at manually adjusting it. Consequently, most of us struggled to precisely fly an NDB approach. (I’m told it could be done, but I’ve never witnessed it myself.)

How to correct a feather on a CDI?

If you’re inbound on the back course or outbound on the front course, the shaded part of the feather is on your left, so you correct by steering away from the CDI.

What is Hsi in IFR?

The horizontal situation indicator (HSI) is a key instrument in IFR flight. It combines the functions of a heading indicator and navigational indicator into a single instrument. For HSI questions, first determine the aircraft heading shown at the top of the indicator. This may allow you to rule out some answers.

Does ILS have a back course?

In cases where an ILS is installed, a back course may be available in conjunction with the localizer. Like the localizer, the back course does not offer a glideslope, but the back course CAN project a false glideslope signal and the glideslope should be ignored.

Why is back course approach bad?

Perhaps because the back course is rarely used, airports are reluctant to spend money installing markers or compass locators . Accordingly, you can expect most localizer back-course final approach fixes to utilize intersections with a nearby VOR rather than NDBs or outer markers.

What is the minimum IFR for back course?

Switch to a localizer with the glideslope generator inop, and minimums became 408 feet and 2,400 RVR. Convert the approach to a circling, however, and minimums rose to 600 and a mile. In this case, VOR and NDB minimums were the same as the bottom numbers for the back course at Orange County.

How to avoid confusion in BC localizer?

To minimize confusion, some instructors suggest making fewer corrections, and then only after major needle deviations. Another trick is to join the BC localizer as far outside the FAF as possible (if you have the option) to help accustom your brain to reverse sensing.

What degree radial is used for Orange County?

In the case of the aforementioned Orange County approach, you’d simply set the front-course localizer heading of 193 degrees on the HSI, and fly the 013 degree radial just as if it was a front-course localizer. Corrections would all be normal, i.e. in the direction of needle deflection.

Why do pilots fly back course?

Flying a back-course approach only serves to reinforce the suggestion that pilots should fly specific headings during instrument flight rather than correct “a little to the right (left).” Rather than choose to correct five degrees left, pick a specific heading that’s five degrees from your current direction, and think that number.

Is it hard to get a back course exam?

The better news is that it ’s equally difficult for an examiner to gain access to a real, live back-course approach (unless they’re willing to conduct his examination at 6 a.m.), so most of the time, you shouldn’t have to worry about demonstrating your proficiency.

Can pilots reverse sensing?

You might think experienced pilots could easily force their brains to overcome the puzzle of reverse sensing. Not necessarily.

What is HSI in OBS?

The HSI is an improvement on the standalone CDI instrument in that it takes into consideration your actual heading. The old CDI would just have a radial set in the OBS and show your deviation (which could have reverse sensing depending on which radial you tuned) in relation to that radial. The HSI serves as a heading indicator as well as a CDI and be coupled to a VOR or a GPS.

What are the inputs of the HSI?

The two inputs of the HSI are the radial or course you want to fly off of a navigational aid (controlled by the OBS – note this doesn’t move the outer ring like a CDI but instead moves the course needle within the HSI to the heading you select) as well as the heading bug (this doesn’t move the heading or the outer ring, but rather just your heading “target” that you can select).

What is CDI in navigation?

A CDI can be its own standalone instrument used for VOR navigation, or it can be part of an HSI which also integrates a heading indicator. When part of an HSI, the CDI is more just the actual course deviation needle on the instrument rather than the entire instrument itself.

Why is CDI confusing?

The reason the CDI can be a little confusing is because it can either be its own standalone instrument (used for VOR navigation) or it can be a component within an HSI (Horizontal Situation Indicator).

What does "to" mean on a CDI?

But if the CDI shows a “TO” indication, you have reverse sensing (meaning that if the needle is deflected to the right, you are actually right of course and must correct to the left). It isn’t a malfunction of the instrument, just something you have to be keenly aware of particularly when flying IFR.

What is HSI in cockpit?

That’s where the HSI (Horizontal Situation Indicator) comes in – a simple but significant improvement to the standalone CDI.

Can you reverse sensing a CDI needle?

Because of this there is a real downside to the standalone CDI instrument and that is you can have reverse sensing.

What is the back course button on a LOC?

When you fly an autopilot-coupled LOC BC approach, ALWAYS push the "back course button" if there's one installed for your autopilot system. By pushing this button, you're telling the autopilot to turn inbound on the back course instead of outbound. Here's the scenario...

What Is A "Back Course" Approach?

When you fly a localizer back course approach (LOC BC), you're navigating to the runway using horizontal guidance off of a localizer system, but in the opposite direction that you'd normally use the localizer. Navigation is very similar to a localizer-only approach, but with a few key differences.

What is the FAA warning about flying back course approaches?

The FAA offers a warning about flying back course approaches: "False glide slope signals may exist in the area of the localizer back course approach which can cause the glide slope flag alarm to disappear and present unreliable glide slope information. Disregard all glide slope signal indications when making a localizer back course approach unless a glide slope is specified on the approach and landing chart."

What degree is the front course of a LOC BC?

For example, if you were flying the LOC BC to runway 17R in Grand Forks, instead of dialing the back course of 174 degrees, you'd dial the front course of 354 degrees, and fly to the needle to navigate the approach.

How accurate is a localizer signal?

Just like a standard LOC approach, the localizer back course signal is only guaranteed to be accurate up to 10 degrees on either side of the runway to 18NM. At an angle of 35 degrees on either side of runway centerline, the useful volume is limited to 10NM. You might receive localizer signals outside of the service volume, but you can't rely on them for navigation.

What is the OBS for LOC BC?

For pilots flying a LOC BC approach using a course deviation indicator (CDI) with an omni bearing selector (OBS), you must pay close attention to "reverse sensing" associated with the back course. According to the AIM, "when flying inbound on the back course it is necessary to steer the aircraft in the direction opposite the needle deflection when making corrections from off-course to on-course. This 'flying away from the needle' is also required when flying outbound on the front course of the localizer."

Where is the LOC BC approach in Grand Forks?

In Grand Forks, ND (KGFK), winds are predominantly out of the northwest. The ILS for KGFK's north-facing Runway 35L is also used to create a LOC BC approach to Runway 17R. Winds out of the south aren't common in Grand Forks, so it saves money to install just one ILS system.

How does the needle move on a HSI?

On the HSI, the needle still moves right when it senses more of the right relative to the arrowwhen it senses more of the right signal. However, the needle points in the selected heading and is rotated with compass. So when you fly a back-course, you dial the normal course of the ILS and since you actually fly opposite direction, the arrow points down and right relative to it is left. And you get normal sensing.

When does positive sensing occur?

For conventional VORs, Positive sensing occurs when the headng currently being flown is on the top half of the VOR. Reverse sensing occurs when the current heading is on the bottom half of the VOR.

How does a VOR needle move?

In VOR, the needle moves normally if you are flying the heading selected and it moves in reverse if you are flying the opposite heading. And when you are flying the opposite heading, the HSI arrow points down, reverting the sensing back to normal.

What is it called when you want an instrument that tells you how to fly to intercept the course?

If you want an instrument which tells you how to fly to intercept the course, it is called a Flight Director.

What is it called when you fly 180 degrees off?

It is worth noting that the autopilots have an "reverse course tracking" switch: If you want an instrument which tells you how to fly to intercept the course, it is called a Flight Director .

Can you reverse sensing a HSI?

Taking this theory to the HSI where the currently flown heading is always on the top half and you can never have reverse sensing.

Can you flip an OBS 180 degrees?

You can always flip the OBS 180 degrees to make that change. I like to think of the HSI as always sensing "positively". You're just tracking the wrong side.

The Rules

• Rule #1
  Always (always!) put the localizer inbound front courseunder the omni-bearing selector (OBS). The OBS setting doesn’t matter to the electronics on a localizer, but this is a good rule as we’ll see a bit further down.
• Rule #2
  If you’re off course on a localizer or a localizer back course approach, and you’re on the side of the localizer feather on the chart that has the shading or other differentiation, the course deviation indicator (CDI) will swing to the left. It doesn’t matter where you’re headed or what you’re doing—…

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Pretty Simple, Eh?