A question on initiating the descent phase...never had this situation before and have done quite a few flights.  As the A/C was approaching the TOD, I changed the ALT from 34000' to 10000' and as always pushed the ALT button to initiate the descent.  The A/C started descending with mode OP DES (per the FMA) but the flight's phase did not change from CRZ to DES (PERF page), the VS window displayed a descent rate of -1700, Thrust Mode was THR/IDLE and in the scratchpad message "NEW CRZ ALT 10000" displayed in white font.  It appeared as if the A/C was adhering to the planned Roll Mode (NAV in the FMA) but was ignoring the planned descent profile.  Can anyone shed any light on what might cause this problem ?  No other exceptions during the flight.

What speed mode were you in?

How far were you from TOD, and ahead or behind it when you pushed the ALT button?

You need to be in managed descent, rather than open descent to follow the profile.

 

It maybe you inadvertently selected OP DES rather than the managed descent mode? Open descent will ignore any profiles or restrictions on the way down to your chosen altitude.  It is a bit of a simplification, but think of open descent just directly descending to your chosen altitude at the chosen speed with the engines near idle. Altitude restrictions and the VNAV profile are completely ignored in open descent.

19 minutes ago, JaneRachel said:

You need to be in managed descent, rather than open descent to follow the profile.

 

It maybe you inadvertently selected OP DES rather than the managed descent mode? Open descent will ignore any profiles or restrictions on the way down to your chosen altitude.  It is a bit of a simplification, but think of open descent just directly descending to your chosen altitude at the chosen speed with the engines near idle. Altitude restrictions and the VNAV profile are completely ignored in open descent.

@JaneRachel I thought that to, but he said he had "pushed", not "pulled" the ALT knob :-/

This is a bug in the Fenix. If this happens again, go to the init page and re enter your original cruise alt and it should recalculate the vpath.

5 hours ago, jcomm said:

What speed mode were you in?

How far were you from TOD, and ahead or behind it when you pushed the ALT button?

As indicated in the OP, speed mode correctly changed from MACH to THR/IDLE.  I pushed, not pulled, the ALT button approximately 15 NM prior to the TOD.

4 hours ago, JaneRachel said:

You need to be in managed descent, rather than open descent to follow the profile.

 

It maybe you inadvertently selected OP DES rather than the managed descent mode? Open descent will ignore any profiles or restrictions on the way down to your chosen altitude.  It is a bit of a simplification, but think of open descent just directly descending to your chosen altitude at the chosen speed with the engines near idle. Altitude restrictions and the VNAV profile are completely ignored in open descent.

Quote

Negative.  I pushed the ALT button and the OP DES display in the FMA was the initial indicator that something was wrong.

 

3 hours ago, chapstick said:

This is a bug in the Fenix. If this happens again, go to the init page and re enter your original cruise alt and it should recalculate the vpath.

Thanks, will do.  I just wonder what is it about this flight/flight plan that triggered this erratic behavior.  I have done quite a few flights in all (3) Fenix variants and have never seen this behavior before.  This flight was with the A321 IAE.

Edited March 13, 20251 yr by zachlog

13 minutes ago, zachlog said:

Thanks, will do.  I just wonder what is it about this flight/flight plan that triggered this erratic behavior.  I have done quite a few flights in all (3) Fenix variants and have never seen this behavior before.  This flight was with the A321 IAE.

Anyway, @zachlog, in your OP you wrote: "pushed the ALT button", and not "pulled"... 

If you PUSH the mode should be "Managed" and not "Open". "Open descent" takes place when you pull the ALT knob. Either you missplelled it or that's another bug in the Fenix (???)

6 minutes ago, jcomm said:

Anyway, @zachlog, in your OP you wrote: "pushed the ALT button", and not "pulled"... 

If you PUSH the mode should be "Managed" and not "Open". "Open descent" takes place when you pull the ALT knob. Either you missplelled it or that's another bug in the Fenix (???)

No misspellings !  The button was pushed, not pulled.  After pushing the button, I checked the pitch mode in the FMA to ensure the descent was managed but it was OP DES and this was the first indicator that something was wrong.  Subsequently, I attempted a second time to have a managed descent.  At approximately the FL325 point, I changed the ALT from 10000' to FL300.  The A/C leveled-off at FL300, I then again pushed the ALT button to start a managed descent, OP DES again.  I managed the rest of the descent and altitude constraints manually, and was able to land....with some extra effort 😀

6 minutes ago, zachlog said:

No misspellings !  The button was pushed, not pulled.  After pushing the button, I checked the pitch mode in the FMA to ensure the descent was managed but it was OP DES and this was the first indicator that something was wrong.  Subsequently, I attempted a second time to have a managed descent.  At approximately the FL325 point, I changed the ALT from 10000' to FL300.  The A/C leveled-off at FL300, I then again pushed the ALT button to start a managed descent, OP DES again.  I managed the rest of the descent and altitude constraints manually, and was able to land....with some extra effort 😀

It's more than evident it's a - rather crude - bug! If the Fenix goes into "Open" instead of "Managed" mode after PUSHING the ALT knob... something is really messed up in it's logic...

I’ve had this experience with the Fenix as well, although not recently. When I posted about the Fenix not descending in managed descent mode, there were comments suggesting that this can result if you enter the target altitude for your descent too soon prior to your destination, or if you try to begin descent too soon prior to the TOD. I noticed that you pushed the altitude knob to commence descent when 15 nm from TOD. Try commencing descent at 5nm prior and see if results change. Also, check on PFD that the aircraft has in fact reached TOC before you dial down the target altitude for your descent. Hope this helps!

Rich

6 minutes ago, rlashier said:

I’ve had this experience with the Fenix as well, although not recently. When I posted about the Fenix not descending in managed descent mode, there were comments suggesting that this can result if you enter the target altitude for your descent too soon prior to your destination, or if you try to begin descent too soon prior to the TOD. I noticed that you pushed the altitude knob to commence descent when 15 nm from TOD. Try commencing descent at 5nm prior and see if results change. Also, check on PFD that the aircraft has in fact reached TOC before you dial down the target altitude for your descent. Hope this helps!

Rich

Since I have been flying the Fenix variants, I always initiate the descent between 5-20 NM prior to the TOD.  I prefer the 10-15 NM range because capturing the angle of descent at the TOD point is much smoother with this range.  I never had a problem in the past with this approach.  This range seems to give the A/C ample time to plan for capturing the descent angle smoothly.  At 5 NM and with the speed at M0.70+, the A/C has to react very quickly to initiate descent, and it does it successfully, but with the downside of a jerkier descent initiation.  However, I will certainly keep the 5 NM recommendation in mind.

Thanks 

Yep, I've had this happen to me on the Fenix.  It is either a bug or I am too early pushing the button for a descent before the descent marker, like zachlog said.  I use FSHUD ATC to initiate the descent when I get the call from "When Ready" which is sometimes 25-30 NM out.  So maybe it is my mistake.   I will keep an eye next time.  

Didn't see an update for some time now...