Question - C-101CC NAV, APR and APR VOR FD Modes

[Charly_Owl]

Hi everyone,

 

I'm almost on the verge of completing the C-101CC guide but I'm still missing some information... mainly about the FD B/C (Back Course), APR, APR VOR and NAV modes.

 

https://imgur.com/JrgILE3

 

What exactly are the NAV, VOR APR and APR flight director modes, what do they do? What's the difference between VOR APR and APR?

 

My (very basic) understanding is that the NAV is associated with a navigation aid like a VOR (however I have no idea of the detection range), while the APR works a bit like a localizer/glide slope tracking for an ILS frequency.

 

Pressing the VOR APR arms the NAV and APR modes. However, I'm not sure what the difference between NAV, APR and APR VOR is. Is APR VOR localizer only?

 

If anyone had a very short tutorial or list of FD descriptions it would be very much appreciated. I have tested some of them, I know they work, but I want to make sure I know what I'm talking about before writing a guide on it.

 

***

 

Also, another question: during an ILS approach, can we use the FD bars or should we only be using the localizer and glide slope deviation indicators on the sides of the ADI?

 

Thanks in advance,

 

Chuck

[Jester986]

I know the FD bars on the ADI work great on an ILS, not sure about the rest of your question.

[Charly_Owl]

I'm asking what's the logic driving the FD bars for NAV, B/C, APR and APR VOR modes.

 

My understanding is that the NAV mode FD bars show corrective commands to steer the aircraft to the selected VOR's radial (a bit like the LOC mode on the 737). There's an ARM light when course isn't captured and a CAP light when course is captured.

 

However, the APR and APR VOR modes confuse me since the APR looks like it sets APR VOR and NAV ON.

[kontiuka]

Ya, some good questions. I'd like to know too. In the EB, the flight director seems a little more straightforward. You just have V/L mode for VOR, TACAN, and ILS localizer steering. And you have the approach arm button which seems bugged at the moment as it doesn't automatically detect glideslope.

[Vibora]

The NAV mode is used to intercept and follow a VOR radial (navigate towards or from a VOR station). This can be also called VOR mode. It can also be used to make a LOC (localizer) approach, when the GS (glide slope) signal has failed or is simply missing. BTW, you can practice this with our module, failing the GS signal in the ME failures section.

 

The VOR APR mode is used to perform a VOR approach. A VOR approach is a type of non-precision approach that can be used in IFR conditions at certain airports when, for example, there is no ILS available. The mode operates in an identical way to the VOR mode (NAV mode) but with optimized gain, which provides more precision for the VOR approach.

 

The BC (Back Course) mode is used when making a BC approach. A BC approach is a type of non-precision approach that uses the back beam of the ILS localizer signal. For example, when there is no ILS for one of the runway directions you can use this type of approach, since all ILS localizer antenna array radiate not only the frontal beam, but a back beam also, of course with lower intensity and lower precision probably. Obviously, to make such a type of approach the corresponding IAL chart has to be published by the country’s civil aviation authority.

 

APR mode is used to make an ILS approach, that is, full ILS with both LOC and GS signals operative. If the GS signal is inexistent or inoperative, you can make a LOC approach and use then the NAV mode of the FD, as described in first paragraph.

 

See the attached pdf for further explanation.

Explanation of some of the C-101CC FD modes.pdf

[Vibora]

And you have the approach arm button which seems bugged at the moment as it doesn't automatically detect glideslope.

I don't know of any bug in glide slope, AFAIK all works perfectly, see the previous post, the glide slope capture mode activates when close to the glide slope. Before the GS is captured, the horizontal bar of the FD continues in ALT mode if it was previously activated (I recommend to do it that way, and of course, intercept the glide slope from below the glide). If you still see some issue please provide detailed info. Though I'm pretty much sure there's none with glide slope.

Edited March 15, 2019 by Vibora

[Charly_Owl]

Thanks! That is a superb explanation, Vibora. I really appreciate it. :)

Edited March 15, 2019 by Charly_Owl

[Rudel_chw]

Me too, :) .. I will test, learn it and then add it to my kneeboard.

[enigma6584]

That is indeed one great explanation. I am off to the course to practice now.

[kontiuka]

I don't know of any bug in glide slope, AFAIK all works perfectly, see the previous post, the glide slope capture mode activates when close to the glide slope. Before the GS is captured, the horizontal bar of the FD continues in ALT mode if it was previously activated (I recommend to do it that way, and of course, intercept the glide slope from below the glide). If you still see some issue please provide detailed info. Though I'm pretty much sure there's none with glide slope.

Ya, tested it and it seems to work but you do have to be pretty close to the centre of the glideslope which is fine. It's just the way the FD used to work, it seemed easier to catch the glideslope. I guess you guess tweaked the logic at some point. Or am I imagining things?

[Vibora]

It was wrong before. The glide slope was captured too early and the FD was commanding to climb instead of keeping the altitude hold mode on.