So tonight while doing my (now nightly) flight - CYEG YEG V21 EPLUR CYYC, I had everything programming into the FMC nicely, including my VNAV, and had just hit 2 minutes from TOD when my flight plan went all screwy. (I'm sure 'screwy' is the proper terminology.)

 

For this flight I had selected the DUVNO2 star with a RW16 transition, and then also selected the ILS approach into RW16.  I'm sure I cleaned up the waypoints properly, it looked like it all made sense and gave me a complete route all the way to RW16.

 

However, when I reached DUVNO on the way to ELERO, my route line changed to show a straight line extending to heading 163, and instead of my from/to on the FMC nav page reading FR DUNVO / TO ELERO , it read FR ELERO and to the course heading for runway 16.  Even though I hadn't reached ELERO yet!  VNAV disconnected with a message, and the AP banked in the direction of that line heading off of my screen. 

 

So, now I'm sure that I did something wrong, and that somewhere someone is chuckling at my puzzlement, but I'd sure like to figure this out!

 

I had saved my flight at 4 minutes prior to TOD since I wanted to make sure I had the chance to retry VNAV if I had messed that up, so I have plenty of opportunity to retry this.  I actually did reload the flight a few times and mess with my flightplan a bit to see if I had maybe deleted a waypoint I shouldn't of, but it still does the same thing.  I did end up finishing the flight by using DTO to ELERO (which is where my route should of been taking me) and resetting VNAV (which I got perfect).

 

But still, does anyone have any suggestions for what I did wrong?

I really shouldn't ask questions like the above late at night; due to a lack of sleep they end up rambling and confused.

 

I really just need to check to see if the issue I had last night was due to my own fault in incorrectly entering a route, or whether it was a bug in the FMC.  I have read elsewhere that people have discovered some issues with various waypoints and such.

 

If anyone cares to speculate, that would be great.

Hi Jim,

 

I think I know what the deal was. Looking at the chart, ELERO is directly in line with your final approach course. When you approach that course and waypoint, your FMS will switch into approach mode. When it does that, it draws an extended line on the approach course. What your AP will then do is intercept that line and allow you to switch over to LOC capture.

 

Try it on a similar airport or approach, I'll bet you'll see the same thing. One that comes to mind is the ILS 23 into Buffalo from the waypoint EHMAN. Around or just when passing EHMAN the approach mode may activate and give you that extended approach line.

 

 

When you approach that course and waypoint, your FMS will switch into approach mode. When it does that, it draws an extended line on the approach course. What your AP will then do is intercept that line and allow you to switch over to LOC capture.

 

I appreciate the help!  That makes sense - it seemed to do exactly as you describe.  Is that intended, or a mistake on my part?

 

What seemed to complicate it more was that I was trying to do a VNAV descent at the time to 5200' at ELERO.  When, as you say, the approach activated, the VNAV I had setup cancelled itself.  I also lost the option to arm / tune / activate the approach on the NAV page.

 

I'm assuming that I set this up in a manner that was bound to cause an issue for me - was there a proper way to have set this route, utilizing the DUVNO2 star and the ILS approach?

I appreciate the help!  That makes sense - it seemed to do exactly as you describe.  Is that intended, or a mistake on my part?

 

What seemed to complicate it more was that I was trying to do a VNAV descent at the time to 5200' at ELERO.  When, as you say, the approach activated, the VNAV I had setup cancelled itself.  I also lost the option to arm / tune / activate the approach on the NAV page.

 

I'm assuming that I set this up in a manner that was bound to cause an issue for me - was there a proper way to have set this route, utilizing the DUVNO2 star and the ILS approach?

 

As I've never flown the Dash 8 IRL, I can't answer with anything other than my experience so far with the addon. What I usually do is tune the approach through the NAV page before I reach that point, then, when it switches over, I'll switch the source and track the LOC. As for the VNAV, you will see it will switch to Pitch Hold. You can stick with that, switch it to an IAS descent, or you can switch to using vertical speed.

 

Different modes will switch the VNAV off, and it also will only work to the reference waypoint. After that you're on your own. Keep that in mind if you only send VNAV to the first constraint of many on a complicated STAR. If there is a way to continue it after I've not yet found how.

 

Just my observations from the flights I've done so far. Whether they are correctly implemented, I couldn't tell you minus what I've read and seen. Obviously I trust they are correct, as Majestic eats and breathes Dash.

 

 

Just my observations from the flights I've done so far. Whether they are correctly implemented, I couldn't tell you minus what I've read and seen. Obviously I trust they are correct, as Majestic eats and breathes Dash.

 

Thanks for your help Kyle.  I appreciate your observations - this is probably the most complex add-on I've yet purchased; when an outcome isn't what was expected it can be hard to tell what was due to simple user inexperience and what is normal!

Thanks for your help Kyle.  I appreciate your observations - this is probably the most complex add-on I've yet purchased; when an outcome isn't what was expected it can be hard to tell what was due to simple user inexperience and what is normal!

 

No problem. I'm learning quite a bit myself going along, which is one of the best parts of complex addons.

Saw this remark about a youtube 400 FMS tutorial, wondered if it could be pertinent to your problem, auto switching to approach mode:

 

"The No LINK prior to the ARRIVAL should not be deleted. This is designed this way so that the aircraft does not commence the approach with being given the clearance from ATC. Provided you have ARMED and TUNED the APPROACH, upon ATC clearance ACTIVATE the APP and the aircraft will do the rest."

 

I was in the habit of deleting "No Link" sections of the plan, I'll look a bit more carefully now.

Eugene

So tonight while doing my (now nightly) flight - CYEG YEG V21 EPLUR CYYC, I had everything programming into the FMC nicely, including my VNAV, and had just hit 2 minutes from TOD when my flight plan went all screwy. (I'm sure 'screwy' is the proper terminology.)

 

For this flight I had selected the DUVNO2 star with a RW16 transition, and then also selected the ILS approach into RW16.  I'm sure I cleaned up the waypoints properly, it looked like it all made sense and gave me a complete route all the way to RW16.

 

However, when I reached DUVNO on the way to ELERO, my route line changed to show a straight line extending to heading 163, and instead of my from/to on the FMC nav page reading FR DUNVO / TO ELERO , it read FR ELERO and to the course heading for runway 16.  Even though I hadn't reached ELERO yet!  VNAV disconnected with a message, and the AP banked in the direction of that line heading off of my screen. 

 

So, now I'm sure that I did something wrong, and that somewhere someone is chuckling at my puzzlement, but I'd sure like to figure this out!

 

I had saved my flight at 4 minutes prior to TOD since I wanted to make sure I had the chance to retry VNAV if I had messed that up, so I have plenty of opportunity to retry this.  I actually did reload the flight a few times and mess with my flightplan a bit to see if I had maybe deleted a waypoint I shouldn't of, but it still does the same thing.  I did end up finishing the flight by using DTO to ELERO (which is where my route should of been taking me) and resetting VNAV (which I got perfect).

 

But still, does anyone have any suggestions for what I did wrong?

I will have a look at this route, hopefully in the next few days, and see what the problem may be

 

 

Saw this remark about a youtube 400 FMS tutorial, wondered if it could be pertinent to your problem, auto switching to approach mode:

"The No LINK prior to the ARRIVAL should not be deleted. This is designed this way so that the aircraft does not commence the approach with being given the clearance from ATC. Provided you have ARMED and TUNED the APPROACH, upon ATC clearance ACTIVATE the APP and the aircraft will do the rest."

 

That might be exactly it... Yes, I was deleting the 'No Link' prior to the arrival.  I'll have to try doing it this way!

 

 

 

I will have a look at this route, hopefully in the next few days, and see what the problem may be

 

I appreciate you taking a look at it Simeon!  I do have a save for this flight approx. 4 min before TOD, if it would help.  I also had this happen last night flying the RNAV 16 approach into CYYC as well.  From the previous behavior, I was expecting it when it happened though.  Perhaps it could be as Eugene had said above, where I was deleting the No Link that gets inserted before the approach?

 

The behavior that occurs (and it was the same each time) was that the approach activates automatically, and it does so when passing the waypoint before the last waypoint prior to the approach. And then the Nav display reads (FR) 'waypoint prior to approach' (TO) 'first waypoint on the approach', even though you hadn't passed the waypoint that it claims you're coming from.  It's like it's automatically activating, but one waypoint too early.

 

For example, on the situation that I first described, my flightplan read:  URPON, DUVNO, ELERO for the star, and then ELERO, CRS 163, RWY 16 for the approach.  I deleted the last waypoint on the star, so that it was simply URPON, DUVNO, ELERO, CRS 163, RWY 16 .  But when passing DUVNO, the approach automatically activated, showing a (FR) of ELERO, and a (TO) of CRS 163, even though in reality I was still 24 nm from ELERO.  ( I may of forgotten one of the approach waypoints that shows in the FMC in my description here, I'm trying to recall this from memory.)

 

And last night, I had the same thing happen on the RNAV approach: While passing DUVNO as part of the star, heading to ELERO, the approach activated, leaving it showing as (FR) ELERO and (TO) PERNA, which is the next waypoint on the approach.

Just thinking off the top...is it possible that you have a duplicate waypoint, for instance, you built a route to a VOR/intersection, but the transition commences at that given waypoint and so it inserts it a second time.  Not very common but I have seen it, very easy to overlook.  Feel free to send me a copy of the saved situation.  I would also recommend that you post this in the MJC forum.

Thanks

I just saw this sort of thing happen tonight too - CYYC-CYVR, route SPRAE2.BOOTH.CANUC2  (departed runway 34, landing runway 08L, FL260 cruise)

As soon as I sequenced the SPRAE waypoint, the route line disappeared completely and my TO waypoint changed to EMKAM, the first waypoint of the ILS08L approach (it should be BOOTH, the next SID waypoint) and the plane started a wide right turn to the north. I was still 300+ miles away from Vancouver when this happened and I'm positive I didn't hit anything to cause it. I have a feeling something's erroneously engaging that approach mode or something like that when it shouldn't be. This has happened on a couple other flights I've done too but I wasn't paying close attention to see how it happened, this time I saw the whole thing.

This is good...thanks for the input.  Ryan I have tried the KPHX dep. and found that is too is not being executed correctly.  Looks like we have to dig a bit deeper into the FMS logic to see what is wrong.  I have already re-cued this to the major bug list.

Yep, I don't think any departure with those kind of psuedowaypoints works in LNAV - I've been flying them all with HDG SEL.