When flying the Longitude I usually import or create flight plans without the approach - I prefer to add these during cruise in case the weather at the destination has changed.  I've had no issue when importing a flight plan which included the approach.  The TODs were correct and VNAV worked well.

However, when I added the approach afterwards, VNAV brought me in way too high... once over 10,000' high and over 20,000' too high on another occasion!  Apparently, if the arrival/approach is added in flight, the destination airport waypoint is not removed from the enroute list.  The G5000 seems to set the TOD way too late and doesn't consider the altitude constraints in the arrival/approach sequences until passing over the airport (which is why I found myself at 20,000').

I found that if, after adding a procedure, I then delete the original airport from the enroute list, I get a proper TOD and the VNAV descent is accurate.  I would think that the real Garmin wouldn't do this, and should automatically remove the airport as an enroute WP if an approach procedure is added to the plan?

1 hour ago, RandallR said:

When flying the Longitude I usually import or create flight plans without the approach - I prefer to add these during cruise in case the weather at the destination has changed.  I've had no issue when importing a flight plan which included the approach.  The TODs were correct and VNAV worked well.

However, when I added the approach afterwards, VNAV brought me in way too high... once over 10,000' high and over 20,000' too high on another occasion!  Apparently, if the arrival/approach is added in flight, the destination airport waypoint is not removed from the enroute list.  The G5000 seems to set the TOD way too late and doesn't consider the altitude constraints in the arrival/approach sequences until passing over the airport (which is why I found myself at 20,000').

I found that if, after adding a procedure, I then delete the original airport from the enroute list, I get a proper TOD and the VNAV descent is accurate.  I would think that the real Garmin wouldn't do this, and should automatically remove the airport as an enroute WP if an approach procedure is added to the plan?

I have shared that experience, in my case with the G3000.  I have edited two pages of my interactive Hjet checklist to remind me to review the plan for just that issue.  First checklist page is the "Before Engines-Start" page which is where entering the flight plan falls in sequence (I load plans from Navigraph/Simbrief).  My Hjet "Cruise" checklist page also contains a check-off reminder to delete the airport if needed after adding the approach during flight if it is listed before the approach.  That in case I load the approach during flight.

I also keep a sharp eye out for manseq's during departure and arrival and forward-manage them as well.

Great to know that I'm not going crazy...

WT has done a wonderful job with all of the Garmin units, but I don't think Garmin would actually leave those WPs intact under those circumstances.

I also attempt to correct/set manseqs as well.

33 minutes ago, RandallR said:

I don't think Garmin would actually leave those WPs intact under those circumstances

Fully agree. Having spent time with actual Garmin GNS and GTN units, as well as with the RXP Garmin-Trainer based simulator GPS models for FSX and P3D, the level of safeguards Garmin builds into its avionics is very significant.

I've mentioned this issue before. Got ignored lol. It might be same issue. Your vnav is way out PROBABLY because the wt unit cannot calculate flight plan route leg /total distances properly. I have video of it seeing 100 miles as 5 miles (shows descent is free fall) then magically passing way point and the 100 miles kicks in. I wave my mouse enthusiastically over the issue in the video! 

This behavior is 100% accurate to the real unit, and will happen on pretty much all Garmin units from the 430 on up.

It is actually a safety feature; in FMC based units, when you add a procedure in this fashion the unit generates a discontinuity and preserves your current leg, so that if you're in LNAV the plane doesn't unsafely swing your guidance in a different direction. It is up to the pilot to then clear the discontinuity and "clean up the box" as pilots say.

Garmin units have no concept of discontinuities, so the way they preserve the leg to avoid sudden guidance changes when you add a procedure is to keep the airport in the same position in the plan; once again it is the pilot's responsibility to clean up the box by either going direct to the desired next fix or deleting the airport leg.

-Matt

3 hours ago, sloppysmusic said:

Your vnav is way out PROBABLY because the wt unit cannot calculate flight plan route leg /total distances properly.

Ever since I began deleting the airport WP after adding approaches the VNAV has been spot-on - no errors at all.

In fact, it's not uncommon for the default ATC to request a descent quite early.  I've found that if I begin a mild descent (to get ATC to shut up) that I eventually intersect the Garmin TOD and VNAV take over smoothly, cancels VS mode and descents exactly on the remaining profile.

42 minutes ago, MattNischan said:

It is actually a safety feature; in FMC based units, when you add a procedure in this fashion the unit generates a discontinuity and preserves your current leg, so that if you're in LNAV the plane doesn't unsafely swing your guidance in a different direction

Interesting.  I guess I can understand this, especially with manseq's.  However, if the Arrival/Approach procedures are added when there are still 5 WPs btwn your current location and the IAF there should be no danger of going off of the planned course.

Does the Garmin unit give some type of warning when this takes place?  Manseq's are noted in the FP, but I don't recall that I ever received any warnings of a discontinuity from the unit after an approach addition.  After the "Load" command the procedures were simply added to the FP (and it took several flights before I figured out that the original airport WP was still in place).

1 hour ago, RandallR said:

Does the Garmin unit give some type of warning when this takes place?  Manseq's are noted in the FP, but I don't recall that I ever received any warnings of a discontinuity from the unit after an approach addition.

Well, it isn't a discontinuity, as Garmin doesn't have dedicated discontinuity legs like other avionics. There isn't a warning, no, as the pilot is expected to review the box after any flight plan changes anyhow to confirm the sequencing is as expected.

Every particular avionics system has its quirks and this just happens to be a Garmin one that throws folks from time to time (along with Activate Approach, which has nothing to do with activating the autopilot approach mode, and confuses pilots and sim users all the time).

-Matt

Edited October 22, 20241 yr by MattNischan

 

Once you get used to reviewing your flight plan it isn't so much of an issue. The one I really have to watch out for is the fact it seems to plan every turn at your current ground speed so if you have tight turns (inc a procedure turn) on the approach then it'll plan a turn the size of Wales until you lose altitude & GS. Which REALLY throws out VNAV & all your distances - same in the CJ4.. ..

G

I establish recommended pattern speeds before approach legs and PTs to prevent this and it seems to work well.  I use 160 KTs for the CJ4 - I haven't been able to find recommended pattern speed for the C700 yet, so I've been using 180 KTs.

7 hours ago, sloppysmusic said:

I've mentioned this issue before. Got ignored lol. It might be same issue. Your vnav is way out PROBABLY because the wt unit cannot calculate flight plan route leg /total distances properly.

That didn't age well. After 3hrs it was obsolete/proven wrong.

I sometimes wonder how people think, that they know how it should be when the only thing wrong is their expectation.

25 minutes ago, fsiscool said:

After 3hrs it was obsolete/proven wrong

Nope