Autopilot Altitude Hold

[dresoccer4]

Hello. I'm having an issue with the AP holding an altitude. I've taken a video to show. The autopilot worked fine during climb phase of flight using the 'speed' setting. However the AP then blew past my altitude preset (FL250). I then manually flew back to the altitude and enabled altitude hold. However the AP then keeps forcing me into a dive. Can someone tell me why it's behaving this way based on the video?

 

https://streamable.com/vsm4jq

[LesOReilly]

All that video shows is that you enabled the AP at 22300 feet with it in ALT HOLD mode...  You gave it no instruction on how to climb back up to your Preselected Altitude of 25000.

[dresoccer4]

13 hours ago, LesOReilly said:

All that video shows is that you enabled the AP at 22300 feet with it in ALT HOLD mode...  You gave it no instruction on how to climb back up to your Preselected Altitude of 25000.

 

and it should have held the current altitude, right?

[molleh]

1 hour ago, dresoccer4 said:

 

and it should have held the current altitude, right?

No, because the altitude is still set for 25,000 in your clip. The autopilot won't do anything in pitch control until you choose VS or speed.

[dresoccer4]

1 minute ago, molleh said:

No, because the altitude is still set for 25,000 in your clip. The autopilot won't do anything in pitch control until you choose VS or speed.

 

ah well i should have taken a longer video because I tried VS and it didn't respond either. also, it was originally in speed mode on ascent and it blew by FL250 until I manually took over. 

[KuntaKinte]

4 hours ago, dresoccer4 said:

and it should have held the current altitude, right?

 

Correct, because the active mode is ALT (which means altitude hold). However, your airspeed could be a factor here, because at this altitude 220 kts is a bit low. And at low speeds the AS CRJ tends to descend by itself.

 

BTW, your video shows another bug of the addon: Since your current altitude differs from the selected one, ALTS should be displayed as armed mode.

[jstnj]

45 minutes ago, KuntaKinte said:

 

Correct, because the active mode is ALT (which means altitude hold). However, your airspeed could be a factor here, because at this altitude 220 kts is a bit low. And at low speeds the AS CRJ tends to descend by itself.

 

BTW, your video shows another bug of the addon: Since your current altitude differs from the selected one, ALTS should be displayed as armed mode.

Yeah there's a few things going on here, and dismissing it all as "user error" would be incorrect.

[Secondator]

Are you able to recreate this issue? If so, what are the exact steps to recreate?

[LesOReilly]

On 5/17/2022 at 5:29 PM, jstnj said:

Yeah there's a few things going on here, and dismissing it all as "user error" would be incorrect.

Ugh ... No it is not incorrect.

 

AP was disabled ... the only modes enabled were ALT HOLD and FMS1 (NAV MODE).  Re-engage AP .. it is not going to climb up to 25,000 Feet just because that is in the ALT Pre-Select.  and the ALTS is not going to show in this case as they have not turned the ALTS since getting into this state... (which we did not see in the video...)

 

Climb profile is 250 to 10K, 290 to Mach Change over (around 27K to 28.5K) when you switch to .74 but some have found better to switch to .76/.77 

 

So yes at 220 knots it is a good chance that they were behind the power/drag curve and thus not able to climb..  

 

Much longer video with how the situation was entered and how it progress is needed.  

[KuntaKinte]

9 hours ago, LesOReilly said:

and the ALTS is not going to show in this case as they have not turned the ALTS since getting into this state...

 

With at least FD active: When the preselected altitude does not match the current altitude, ALTS will always appear as armed mode - the only (normal OPS) exceptions to this are GS capture and go-around mode. You then have two choices:

• re-select the preselected altitude to your current altitude => PFD: ALTS armed mode disappears while ALTSCAP becomes active mode, then ALTS becomes active mode
• climb to preselected altitude => vertical mode necessary (either SPEED, IAS, V/S, PITCH) to leave the current altitude.

[dresoccer4]

On 5/17/2022 at 6:34 PM, Secondator said:

Are you able to recreate this issue? If so, what are the exact steps to recreate?

i haven't flown since this but when i try again i'll report back