GTN 750 skipping fixes on approach

[ckelly14 7]

Dropped in the GTN 750 in the King Air 350 and had an issue.  Loading up an approach and activating it, the GTN always points me to the second approach point, instead of the first like the G1000 and GNS 530.  For example, activating vectors to the ILS 8 approach into EGHH, the GTN shows the active waypoint as FF08 instead of CF08.  Also, the course to that fix is incorrect.  It shows the desired course to be to be 76, which is actually the course from CF08 to FF08, not the course from my current position to FF08.  

 

Not sure but it seems that when I activate an approach and vector for finals, the GTN thinks I am at CF08 heading to FF08.

 

I hope that makes sense...

 

[richjb2 195]

ckelly,

That appears to be correct.  Activating the vectors to final function extends the published final approach course out from the final approach fix to permit ATC radar vectoring to join the extended final approach course.  The final approach fix for the ILS DME or LOC DME Rwy 08 at EGHH is the I-BHM 4.4 DME, which has a charted computer navigation fix (CNF) of [FL08].  That might be coded as "FF08" depending on which navigation data source you're using (Garmin's, Navigraph, or Aerosoft). Vectors to final will extend the published final approach course (076) out from FL08 to allow the aircraft to join the extended final approach course. 

The CF08 is a fix that is often inserted into approach coding as per the ARINC 424 coding specification.  This fix is called a Final Approach Course Fix (FCAF) and is set at the nominal limit of the localizer service volume. In the US, we name these fixes using a CNF. 

I appears that the GTN 750 is working correctly.

Rich Boll

[ckelly14 7]

Great explanation, thanks.  I guess the GNS 530 isn’t working correctly.  So I would need to fly to somewhere along the final approach course before activating the approach?  What does “vectors to final” really mean, guess I have been doing it incorrectly the whole time??

[richjb2 195]

The pilot activates "vectors to final" when ATC is radar vectoring the aircraft on to the final approach course.  In the US, ATC will provide headings (i.e., "vectors") that bring the aircraft to a position to intercept the final approach course extended out from the final approach fix (FAF) at a distance of 3 NMs, which is one mile outside of the approach gate (an imaginary position 2 NM from the FAF).  The intercept angle or final heading will be no more than 30 degrees from the final approach course.  

what I do in the simulator is to activate vectors to final and then monitor my position on the moving map.  I try to provide myself with ATC vectors that will bring me perpendicular to the final approach course about 5 miles out from the FAF, followed by an intercept vector of 30 degrees when I am about 2 to 2.5 NM from crossing the final approach course extended out from the FAF. 

I'm not sure how well P3D or FSX's ATC would do it, but I imagine it would react in a similar manner.

Rich 

[Bert Pieke 7,584]

The alternative is to select a specific approach point instead of vectors.

Via: xxxx

Then the autopilot will fly you onto the final approach, using NAV mode..

Edited October 20, 2019 by Bert Pieke