Flying a Backcourse - CDI

labbadabba

labbadabba

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labbadabba
If you're flying a backcourse approach, wouldn't it make sense to just set the CDI to reciprocal heading (i.e., the inbound course on the ILS)? That way you eliminate the reverse sensing stuff, right?
 
Doesn't work that way unless you have an HSI I'm pretty sure


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Traditional CDIs don't respond to the OBS at all when displaying a localizer.

HSIs do, but the trick has limitations. If you want to couple it, you can't turn it backwards. And G1000s really don't like it if you turn the course backwards. You get an alert.

The "right" way is just to learn how to read the reverse sensing. It's not hard at all. When coupling, make sure you push the BC button.
 
Exactly, the trick works on the hsi basically because you're essentially turning the cdi upside down....

But the BC setting knows how to fly it "backwards"


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gsengle said:
Doesn't work that way unless you have an HSI I'm pretty sure
Click to expand...

That should be correct.

The "mental trick" I learned and then taught was this...

Normally, you imagine you're the "donut" and the CDI represents the course. Simple enough, needle right means fly right and so on.

If reverse sensing is unavoidable, the trick is to place the plane on the needle, so that the donut represents the course. So, if the needle is right you would fly left towards the donut.

May seems silly, but it works!
 
VORs work by transmitting two signals from which the receiver can determine which radial it is on. Localizers work by transmitting two signals from which the receiver can determine whether it is on the blue or yellow side of the course. The OBS knob is used to set the desired radial, which works for VOR signals but not localizer signals. The receiver knows whether to show a localizer deviation or a VOR radial deviation based on the frequency that you have selected, since a handful of frequencies are set aside for localizers.
 
iamtheari said:
VORs work by transmitting two signals from which the receiver can determine which radial it is on. Localizers work by transmitting two signals from which the receiver can determine whether it is on the blue or yellow side of the course. The OBS knob is used to set the desired radial, which works for VOR signals but not localizer signals. The receiver knows whether to show a localizer deviation or a VOR radial deviation based on the frequency that you have selected, since a handful of frequencies are set aside for localizers.
Click to expand...

yeah, I had a 'duh' moment... Thanks
 
labbadabba said:
yeah, I had a 'duh' moment... Thanks
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Those happen to me all the time, so I try to take advantage of them by learning way more than I should on the topic.
 
I've never flown a back course for real. And if you have an approach GPS you'll never need to for sure.


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gsengle said:
I've never flown a back course for real. And if you have an approach GPS you'll never need to for sure.
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Click to expand...

I've done quite a few in training. We have 3 of them within a 50 mile radius of KC.
 
Yes, in training. Not for real.


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gsengle said:
I've never flown a back course for real. And if you have an approach GPS you'll never need to for sure.
Click to expand...

I've done a backcourse SID for real. KSPB CREPE THREE. Never an approach -- there aren't that many (though there is one at KSMX -- haven't flown there IFR, though).
 
Do you have an approach cert GPS?


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Heh ok masochism excepted ;)


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MAKG1 said:
HSIs do, but the trick has limitations.
Click to expand...
The CDI is still unaffected, it's just that it's rotated "upside down" if you've set the course arrow right. That's why the autopilot needs the BC button.
 
gsengle said:
I've never flown a back course for real. And if you have an approach GPS you'll never need to for sure.


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Click to expand...

That's now it worked for me. Not long after finishing IR, I headed down to visit the inlaws at KFAY, Approach vectored down between some cumulus so I didn't get any actual . . . yet. Then they told me to expect the ILS BC for the runway, which I had never even had the opportunity to practice in training. I told them (I'm sure I sounded less-than-thrilled) that I was expecting ILS BC whatever, but I would prefer GPS whatever. They immediately cleared me for the GPS approach and life was good. THEN I logged some actual getting down through the deck, a simple task on a GPS approach. Six years later, that's still the only Back Course I've ever been offered.
 
One of the first things they did creating GPS approaches was to create overlay or approaches based on existing ones where the TERPS (terrain clearance) was already worked out... I bet there is always a GPS option for these odd approaches....


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bobmrg said:
There are only 34 of them left. Soon it will not be a problem.

Bob
Click to expand...

Is there a list of them somewhere? There are a few of them around my area, I didn't realize they were so rare.
 
Always set the inbound of the front course. You will never be wrong.

The most deceiving is the missed at ASE.
Set the inbound front course...
 
Kritchlow said:
Always set the inbound of the front course. You will never be wrong.

The most deceiving is the missed at ASE.
Set the inbound front course...
Click to expand...
Always?

G1000 will alert and the FD will indicate turns away from the BC. Set the course you intend to fly on that platform. Which it will do for you if you don't override it.

It's a lot more general to learn the reverse sensing. That even works on CDIs.
 
MAKG1 said:
Always?

G1000 will alert and the FD will indicate turns away from the BC. Set the course you intend to fly on that platform. Which it will do for you if you don't override it.

It's a lot more general to learn the reverse sensing. That even works on CDIs.
Click to expand...
With a regular HSI?? Yes.
Not sure about some synthetic software changinging the rules.
 
gsengle said:
One of the first things they did creating GPS approaches was to create overlay or approaches based on existing ones where the TERPS (terrain clearance) was already worked out... I bet there is always a GPS option for these odd approaches....
Click to expand...
Yep... but of course the overlay approaches were only temporary stopgaps until actual RNAV/GPS approaches were in place. In most cases they have been retired by now.

And I know of at least one GPS overlay that wasn't replaced with an actual approach - the VOR-A at KVLL no longer has an overlay, and there was no GPS-A to replace it. That might be because there is now (and has been for quite a while) a RNAV/GPS to rwy 9 that is far preferable to the old overlay anyway. But the fact remains that at one time you could fly the VOR-A even when the PSI VOR was OTS, and now you can't.

(Come to think of it, I have no idea what the status of that VOR is at the moment. I heard it was back in service, but there was a notice quite a while ago that they intended to shut PSI down. Anyone know what happened to it?)
 
azure said:
And I know of at least one GPS overlay that wasn't replaced with an actual approach ... VLL
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Correct, the plan was to provide some RNAV approach at each field, not to necessarily overlay an RNAV over each existing approach.
The RNAV 9 suffices (and it has circling minima). It's not clear what you've lost. You can even start that approach at ZARIM (the IAF of the VOR-A) or even the PSI VOR as both are within the TAA.
 
PPC1052 said:
How many missed procedures have you fly a back course? I know of at least two.
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Flying outbound on the back course requires no changes. The needle sensing is correct. Now if your missed approach procedure required you to fly outbound on the front course, then you'd have the same issues you have flying inbound on the BC.
 
flyingron said:
Flying outbound on the back course requires no changes. The needle sensing is correct. Now if your missed approach procedure required you to fly outbound on the front course, then you'd have the same issues you have flying inbound on the BC.
Click to expand...

That's what I mean. (For example, KTYQ ILS or LOC 36), and I suspect that there are many others. Thanks for the clarification.
 
Watch out if your are flying with an Aspen. You have to set the course as published or it won't recognize that it's a B/C. I found that out when training my last IR guy. I always had him set the plane up like an HSI till that gem popped up.
 
Plano Pilot said:
ASE is the only one I know of.
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The LOC-DME approach at ASE flies outbound on a back course (albeit a different one than the LOC the approach is based on). Flying outbound on a BC does not yield reverse sensing. The TYQ approach mentioned earlier flies outbound on the front course and that indeed has reverse sensing.
 
ARFlyer said:
Watch out if your are flying with an Aspen. You have to set the course as published or it won't recognize that it's a B/C. I found that out when training my last IR guy. I always had him set the plane up like an HSI till that gem popped up.
Click to expand...
You've lost me. The ASPEN manual says "set the CRS to the front course localizer or ILS approach value." This is exactly how you set an HSI. What are you saying is different?
 
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