Jump to content

Localizer Autotuning


dlrk
 Share

Recommended Posts

There’s a whole complex dance that the FMSs have to execute, but in normal ops the conditions are:

  • There is a suitable (read: LOC or ILS) approach procedure linked in the flight plan that the plane is in, or that is coming up down track in your FPL;
  • The plane is within 31nm of the approach airport
  • Upvote 3
Link to comment
Share on other sites

Should it do anything else than just tune the frequency alone? I'm not sure if I'm doing something wrong (or if I'm just too impatient) but every time I've tried to fly an ILS approach on LNAV so far, the ILS did not seem to activate by itself although approach mode was armed. The frequency gets auto-tuned but I appear to need to manually switch the Nav Source. The course also always remains pre-selected at 0°, even after the ILS has already been auto-tuned.

What I would have expected to happen from similar auto-tune functionality on other aircraft systems if I remember correctly:

  • localizer course for the selected approach gets automatically entered into the localizer pre-selection window
  • ILS identification is being displayed while still on LNAV (maybe I just did not find it on the displays?)
  • localizer & glideslope indicators become visible when in range
    • that sort of appears to happen if I change from LNAV to heading mode (blue bars?)
  • if approach mode is armed, AP should switch automatically from LNAV to LOC & GS

Maybe the Challenger's systems just work differently and don't do that? But I think it's more likely that I'm still doing something wrong or maybe I'm just still a bit lost on the displays. Would be good to have a confirmation if any of the points listed above are actually being performed by the Challenger and when/how that happens. :) 

Edited by EnQ
Link to comment
Share on other sites

The course will never appear in preset nav, that’s one of the oddities of nav-to-nav transfer (the name for FMS to ILS auto-transition), and why I recommend setting it manually if radar vectors are expected. I found this weird too, and not how I would have designed it, but it’s just how the Challenger is.

When nav-to-nav transfer is able to work, you’ll see blue indications of localiser and glideslope deviation, both as blue diamonds on the deviation scales in the attitude/svs part of the PFD, as well as the CDI at the bottom with blue dashed “ghost” needles.

You should have FMS1 as the nav source on the left side, and FMS2 on the right side. Make sure baro settings are sync’d too.

Press the approach mode on the autopilot and you should see white LOC1 and GS indications on the FMA strip at the top of the PFD. Even then, it will hang onto FMS nav for as long as it can, until nearly established on the final approach track, then it will swap to LOC navigation. If you’re not on the glideslope, you may need to adjust VS or pitch to capture the glide properly.

Normal pilots rules apply : if it’s not doing what you expect, don’t just sit there, make it do it! Change nav source manually and fly the ILS. This is why, personally, I always set the course on preset nav as part of approach preparation.

Hope that makes sense. 

Edited by Graeme_77
  • Like 1
  • Upvote 2
Link to comment
Share on other sites

I was having the same issue. 
From the Bombardier docs, looks like 30 nautical miles and less than 105 degree intercept (section 04-10-50 page 201 of volume 2 of the flight crew operations and section 04-10-30 page 181).

You need CDU1 and CDU2 to have the same flight plan active (I just copy CDU1 from CDU2 and for good measure put a copy in CDU3 as well).  It took me a while to realize the copy of approach (localizer) data between the flight computers wasn't automatic on this aircraft (there apparently isn't a primary FMS that can be selected), and importantly there is no message that localizer/glideslopw capture is disabled such as "LOC UNABLE" via a message on the CDU when the avionics don't have at least two independent systems to track from.  This had me plow the internets and landed me in Smartcockpit's documentation on the Challenger 605 which also uses the Collins Pro 21 avionics.  The 605 is similar to the 650 except for engines and range looks like but it looks pretty much the same in terms of operations.

Edited by Muchimi
  • Like 1
Link to comment
Share on other sites

  • 9 months later...
On 1/16/2022 at 2:48 AM, Graeme_77 said:

The course will never appear in preset nav, that’s one of the oddities of nav-to-nav transfer (the name for FMS to ILS auto-transition), and why I recommend setting it manually if radar vectors are expected. I found this weird too, and not how I would have designed it, but it’s just how the Challenger is.

When nav-to-nav transfer is able to work, you’ll see blue indications of localiser and glideslope deviation, both as blue diamonds on the deviation scales in the attitude/svs part of the PFD, as well as the CDI at the bottom with blue dashed “ghost” needles.

You should have FMS1 as the nav source on the left side, and FMS2 on the right side. Make sure baro settings are sync’d too.

Press the approach mode on the autopilot and you should see white LOC1 and GS indications on the FMA strip at the top of the PFD. Even then, it will hang onto FMS nav for as long as it can, until nearly established on the final approach track, then it will swap to LOC navigation. If you’re not on the glideslope, you may need to adjust VS or pitch to capture the glide properly.

Normal pilots rules apply : if it’s not doing what you expect, don’t just sit there, make it do it! Change nav source manually and fly the ILS. This is why, personally, I always set the course on preset nav as part of approach preparation.

Hope that makes sense. 

One of THE most important posts on this forum! 

Thanks Graeme

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...