Glide Slope/LOC and Magenta Diamond - Question

[ck777 2]

Okay...I'm trying to figure out what I did wrong on an approach yesterday.  I was flying into Indianapolis, KIND, rwy 5R.  It was pretty much straight in, since I was coming from the SW.  I cross KELLY around 5000 ft (I think).  I selected that runway in the FMS.

 

I can't remember when I picked up the LOC but it was a white diamond.  I looked up in the FCOM v 2., 10.10.14, and it is the Anticipation Cue.  I also got the white diamond  for the glide slope.  So, I'm making my merry way into 5R and noticed the white diamonds never turned to the magenta diamond.  So i look on pg 10.10.16 and says "fills in solid when within 2 1/2 dots from the center".  I never saw this happen.  Any ideas on what I did incorrectly or where I can find this in the manuals?  I promise, I've tried looking through them.  Maybe I spaced out and selected the wrong runway (05L)...

 

Cheers

 

 

[scandinavian13 5,192]

 

 

Maybe I spaced out and selected the wrong runway (05L)...

 

Could've been it.

 

Also, remember that the nav data in FSX itself is over a decade old now, so the nav data that you get from Navigraph (or others - which is current) is out of sync due to magnetic variation. That being said, your LNAV track could have been ever so slightly off of the LOC course, and never actually captured.

 

In the States, we'd never really LNAV onto a final approach course, unless you'd flown a transition for that approach (example - the IAD Runway 1R transition off of BRV). Even though the transition exists, it's rarely ever flown in favor of vectors to final, which helps optimize the flow of aircraft to the runway.

 

Being on vectors would essentially sidestep the issue of the LNAV track being out of sync with the old FSX data because, instead of being only a degree or two off (enough to throw intercepts off), vectors are usually on a 30 degree intercept.

 

This is actually partially discussed at the end of tutorial one as well.

[ck777 2]

Thanks, Kyle

 

I decided to uninstall FSX, OS, and re-do everything....wait for it....wait for it.  Just kidding

 

Good point about FSX; I had forgotten about that.  I don't think I was on LNAV but I really don't remember.  I may go fly a circuit to see what happened but doesn't seem like a big deal.

 

Yeah...I've landed 1R quite a few times with ATC and never done the BRV transition (VATSIM).

 

So, help out my sleep deprived brain (I have a newborn in the house).  Why does a 30 degree intercept not throw off FSX data but 1 or 2 degrees does?

[scandinavian13 5,192]

 

 

Good point about FSX; I had forgotten about that.  I don't think I was on LNAV but I really don't remember.  I may go fly a circuit to see what happened but doesn't seem like a big deal.

 

If you weren't on LNAV, what were you? HDG SEL? If HDG SEL, then I think it wouldn't have been white. The white diamond is there because the magenta cue is being used for LNAV until the point the LOC cue becomes active (this automatically happens if you have LOC or APP armed). I believe that if you're on HDG SEL, with LOC armed, the primary cue would've been the LOC (and it wouldn't have been white).

 

 

 

So, help out my sleep deprived brain (I have a newborn in the house).  Why does a 30 degree intercept not throw off FSX data but 1 or 2 degrees does?

 

Think about it:

One or two degrees off between two courses means that it will take a very long time for them to converge. Thirty degrees means that they will converge more quickly.

 

Mathematically, for two lines only 1 nm apart (assuming the intercept angle is how you're traversing between the two):

An angle of 30 degrees will have you intercepting the new course at only 2 nm.

An angle of 1 degree will have you intercepting the new course at 57.3 nm.

 

In other words, the relatively more extreme intercept angle of a vectored intercept forces you onto the LOC course (in addition to the fact that ATC must have you intercept no later than 3 nm from the FAF, at least when using a 30 degree intercept), while the 1 degree difference (with a convergence on the runway threshold in this case) never really places you on the new line.

[ck777 2]

Makes total sense, thanks for the info.  I'm sure I was on LNAV, hence the white diamond

[777simmer 117]

Hi there.

 

yes, the confusing ghost pointers...."anticipation cue" actually.

First, Yes you were on Lnav.....otherwise you would not have had the white ghost pointers.

In HDG sel mode, as soon as the Loc is received, it will show an open magenta diamond (not white)......just like it allways looked like before we had Lnav and Vnav aircraft.

But why do we have ghost pointers?

 

The ghost pointers were invented when Rnav approaches were introduced.

Before Rnav approaches, those LOC/GS diamonds were only used for Loc and GS deviation.

And on the left top of the PFD, you would see what theses diamonds refered to......(to the ILS frequency displayed there).

 

But now that we also use Lnav and Vnav for approaches, with the same diamonds, you need a way to identify what the diamonds are linked to.

Are they displaying a Loc deviation or an Lnav deviation?

 

So on top/left of the PDF we now not only have the ILS frequency displayed, but also Lnav/Vnav.

This is important because:

- with Ils frequency top/left: the diamonds give Loc and GS deviation

- with Lnav/Vnav top/left: the diamonds give Lnav and Vnav deviation from your programmed FMC path.

 

Do not mix this up with the FMA (flight mode Anunciation) indications on the very top of the PFD (HDG Sel/FLCH SPD/ Lnav/VS etc) as they indicate what mode the AP or FD is in.

Not what the diamonds refer to!

 

When you are in Lnav then the diamonds will automatically show Lnav and Vnav deviation.

So how do I see when the LOC/GS become alive if I want to fly an ILS?

That is where the white ghost pointers come in :-)

 

But dont forget to arm APP mode!

Because them pointers will just stay white as long as your AP/FD are in Lnav/ Vnav mode.

Without APP armed (or if Loc never captures for other reasons, like parallelling) the FMA will stay in Lnav/Vnav, on the top/left of the PFD it will say Lnav/Vnav and the diamonds give Lnav/Vnav deviation.

The whole system would never switch to Loc and GS on the FMA, nor ILS frequency on the top left of the PFD and the ghost pointers stay white to indicate you are receiving the ILS, but you have not told the AP/FD to actually follow it.

 

The FCOM SOPs actually advices you to not intercept an ILS from Lnav but use HDG Sel instead.

It is possible and we do Lnav to loc intercepts in real life as well.....but allways with the back of our mind thinking.......hope it captures!

Because as Kyle said, Lnav may parallel the Loc all the way untill short short final. Even if this is only paralleld by a little, it is possible for the LOC to never capture.

If that happens (parallelling) then just engage HDG sel for a second, steer to the left/right to intercept the loc and arm APP again.

[ck777 2]

Rob,

 

Thanks so much for taking the time to explain in depth; it's really helpful!

 

C.