Unable to shut off VNAV v1.1

[Tim013]

Just did a quick flight from KSDF to KMDW.  I programmed an RNAV approach, and this may be the first time I've tried an RNAV approach with the 733.  Anyhow, I don't care for VNAV much, so I always fly with LNAV activated, and I control altitude and speed with the MCP.  However, during this flight, everytime I crossed a waypoint, the VNAV would turn on, and try to take control.  I would then turn it off, and resume MCP control, but at the next waypoint, the VNAV would come on again.  I eventually just turned LNAV off, and that stopped VNAV from coming on by itself.

Question:  If a RNAV approach is selected, does this then force the use of VNAV during the flight?

Tim

[Litjan]

Hi Tim,

that is really weird. VNAV can not turn itself on, really, and it can´t be "armed" either (unlike in the NG). So I have really no idea what went wrong there.

We have the whole VNAV code slated for a complete makeover in the next few months, and this will likely cure whatever brought this phenomenon about. But for now rest assured that you did nothing wrong and probably just hit a weird quirk in our code.

Cheers, Jan

Edit: If you see the FMA column (on the very left) cycle during VNAV use (i.e. RETARD, IDLE, FMC SPD,...) this is normal behaviour during VNAV usage.

Edited July 9, 2017 by Litjan

[Tim013]

That's good to know. 

Thanks for the response.

Tim

[blocks_off]

Maybe cycling the AP and FDs off might disengage it?

[Tim013]

Cycling the AP and FDs did not help.  I actually did a second flight, and had the same thing happen.  The VNAV came on with A/T on, but everything else off.  I even tried to bind a button to the VNAV toggle, in an effort to stop it, but no joy.

The only thing I've done recently is update the FlyJSim 727, but that is an SASL aircraft I think, and doesn't use Gizmo at all.

Quite the mystery at the moment.

Tim

[tkyler]

indeed that is one we have never seen.....if its a quirk in our code, then I'm thinking maybe our code is self-aware and writing itself    As Jan said, we're going to do a revamp here in the near future.

-tkler

[Litjan]

If you could capture a video of that I would be really interested to see it!

Thanks, Jan

 

[Tim013]

12 hours ago, tkyler said:

indeed that is one we have never seen.....if its a quirk in our code, then I'm thinking maybe our code is self-aware and writing itself  

-tkler

That's why the creator has to be careful what he creates.  One day, you may be enslaved by your creation....lol

Here's a clip. 

https://clips.twitch.tv/ResourcefulBovineAntelopeDBstyle

 

Tim

[Litjan]

Hi Tim,

I think this is what is happening:

When I look at the very first second of your video, I can see that you are in a peculiar protection situation - the barber pole (max speed) is still at 230 kts, which indicates that you JUST retracted the flaps, and most likely got into an overspeed situation where the autothrottle reversion mode is trying to prevent a flap placard bust. Hence the MCP SPD both in the autothrottle and pitch channel FMA.

Once the flaps fully retract, the overspeed situation is rectified and the plane reverts to VNAV SPD climb. Why it does that I don´t know, it should actually go back to FL CHG climb.

I would dare to say that the protection situation (reversion modes) is a bit of a black hole, and the flight manual isn´t very clear about those either. I don´t have much (any) experience with those in the real plane or simulator (I am proud to say). We have coded it to act like described in the flight manual, but it isn´t very clear on what happens when you exit the overspeed situation. I see that the plane goes back to MCP SPD and CWS P when you push the VNAV button, as expected.

Try to fly the departure again and make sure that you don´t bust the placard speeds and see if it still happens.

Cheers, Jan

 

[mfor]

Well he said: "However, during this flight, everytime I crossed a waypoint, the VNAV would turn on, and try to take control. "

This sounds more like an addon that automatically engages VNAV when crossing a waypoint - unless he overspeeds on every turn. So I'd recommend disabling everything except for ixeg (and gizmo) and see if it is still happening.

 

[Tim013]

 

29 minutes ago, Litjan said:

Hi Tim,

I think this is what is happening:

When I look at the very first second of your video, I can see that you are in a peculiar protection situation - the barber pole (max speed) is still at 230 kts, which indicates that you JUST retracted the flaps, and most likely got into an overspeed situation where the autothrottle reversion mode is trying to prevent a flap placard bust. Hence the MCP SPD both in the autothrottle and pitch channel FMA.

Once the flaps fully retract, the overspeed situation is rectified and the plane reverts to VNAV SPD climb. Why it does that I don´t know, it should actually go back to FL CHG climb.

I would dare to say that the protection situation (reversion modes) is a bit of a black hole, and the flight manual isn´t very clear about those either. I don´t have much (any) experience with those in the real plane or simulator (I am proud to say). We have coded it to act like described in the flight manual, but it isn´t very clear on what happens when you exit the overspeed situation. I see that the plane goes back to MCP SPD and CWS P when you push the VNAV button, as expected.

Try to fly the departure again and make sure that you don´t bust the placard speeds and see if it still happens.

Cheers, Jan

 

How dare you impune my flying skills sir! 

I will continue to try and sort it out.  I've just removed all VNAV button commands from my controller viat the .prf files, and will see if that works.  If it doesn't, I'll dig deeper.

Thanks,

 

Tim

[Litjan]

Thanks for helping me check this out!

Cheers, Jan

 

[Tim013]

I'm not claiming victory, but I just made the KSDF to KMDW flight again, and this time VNAV behaved, and stayed in it's cave.

Prior to starting X-Plane, I deleted any HOTAS buttons assigned to VNAV.  There were two of them in my .prf files.  This is really, really, really strange, because other than A/P on and off, I've never, and I mean NEVER assigned any advanced A/P functions to my controller.  I have no idea how these became programmed to my HOTAS.  While I'd like to suspect those darn Russian hackers, I'm at a loss to explain it.

The bottom line is I think the HOTAS button that got assigned to toggle VNAV on and off was noisy, and would randomly turn on the VNAV.  That's the best I can come up with.

Unless it happens again, I'll consider the issue resolved.  If it does rear it's ugly head again, I'll report back.

Tim

[Litjan]

Hi Tim,

crossing my fingers that that was the problem... keep me informed if it happens again!

Thanks, Jan