[Solved]Cannot engage VNAV, 737-300 v1.1 in XP11

[stolowski]

Ok, I need an advice, this is driving me crazy... For some reason I cannot engage VNAV mode. There must be something I'm doing wrong (hopefully)...

I'm taking off from LOWI, destination is LSZH. Flightplan created in PFPX. I'm using latest AIRNAC from Navigraph. The route, departure and arrival are all entered, discontinuity removed. I've set speed/alt restrictions for a few waypoints that missed them. TAKEOFF speeds set. TRANSITION alt in the FMC set to 10000. Fuel, gross weight set. MCP alt set to either the alt of the first waypoint (e.g. 3600) or higher (up to CRZ alt - I tried different ones in all my attempts). Shortly after takeoff, a few hundreds ft AGL I engage LNAV and turn autopilot ON. I continue climbing and after a minute or two (definately above the minimums required to engage VNAV) I start trying to press VNAV button, but cannot engage it. Sometimes when I'm really high (e.g. above FL110) suddenly I can engage it...

I'm confused and not sure what am I missing that prevents VNAV from engaging after takeoff and above 1500ft AGL... Certainly something is different than in 757, 767 or 737-800 that I occasionally fly too. Any suggestions? Is this some kind of incompatibility with XP11?

Edited June 1, 2017 by Morten

[Morten]

Try to do this flight, step by step and see what happens..

 

[WR269]

I had this exact problem which forced me to remove the aircraft and not fly it for over 6 months.

I did a fresh clean install of XP11 due to something unrelated and when i installed 1.1 the problen appears to have gone away.

Sent from my SM-G935F using Tapatalk

[mmerelles]

15 minutes ago, WR269 said:

 

I had this exact problem which forced me to remove the aircraft and not fly it for over 6 months.

 

I did a fresh clean install of XP11 due to something unrelated and when i installed 1.1 the problen appears to have gone away.

 

Sent from my SM-G935F using Tapatalk

 

if this happens to you again is quite important:

a. You do some screen captures while the problem is going on to see what all the displays and annunciators says

b. Also please share your flight details. origin/destination airport, sid, star, init perf page, etc. everything to reproduce the problem

 

i do understand the frustration, in the other hand it is simply not possible to test unlimited scenarios under development & beta. User input is also necessary for the devs. The same that happens on the real thing with fmc issues reported by pilots and fixed by manufacturers over firmware updates.

[WR269]

2 hours ago, mmerelles said:

 

if this happens to you again is quite important:

a. You do some screen captures while the problem is going on to see what all the displays and annunciators says

b. Also please share your flight details. origin/destination airport, sid, star, init perf page, etc. everything to reproduce the problem

 

i do understand the frustration, in the other hand it is simply not possible to test unlimited scenarios under development & beta. User input is also necessary for the devs. The same that happens on the real thing with fmc issues reported by pilots and fixed by manufacturers over firmware updates.

Understood, but it was very much a wide issue....no matter what flight, what route.

I never loaded a flight plan, always entered it manually.

Always entered SID and STAR before departure.

Always started Cold and Dark. No Disco items in FMC, no issues whatsoever.

When the issue started, I was unable to engage VNAV until about 20,000ft....later flights i could not engage at all.

Funnily enough, LNAV engaged without a problem, but VNAV refused....nothing in vertical navegation worked, Altitude Hold, Alt Select, Vertical Speed of FL CHG, not one of them worked....if I had autopilot on and flying on LNAV...if I pressed any of the vertical modes above, autopilot would disconnect. Very strange. I removed all plug ins, reintalled countless times....nothing worked.

When I installed the new 1.1 on a brand new version of XP11, the very first flight I did had VNAV disconnect 3 times in flight, but the autopilot did not disconnect....I was able to re-engage VNAV and flight continued. I reinstalled the IXEG once again and have done 2 more flights repeating the original, and the issue has not happened again so fingers crossed I have it behind me.

 

[mmerelles]

36 minutes ago, WR269 said:

Funnily enough, LNAV engaged without a problem, but VNAV refused....nothing in vertical navegation worked, Altitude Hold, Alt Select, Vertical Speed of FL CHG, not one of them worked...

This behavior is a pretty solid evidence that you use a yoke/joystick which is sending noise spikes from the pitch potentiometer (thus affecting all vertical modes), when you try to engage any vertical mode plane refuses because it is receiving pitch input from the controller and the aircraft "thinks" you are manipulating the yoke to override and regain control.

This can be confirmed having a screen capture of the displays and annunciators, but being blind it is just an assumption. I am 99% sure this is the problem but please share a screen capture if this happens again and i can help you quite easy on  this.

 

Please don't get me wrong, I am not saying VNAV has no issues. It actually has and the devs have confirmed they will rework vnav, but sometimes having screen captures helps to understand other problems that we assume are all vnav or if it is vnan we can document them properly so when vnav testing comes we make sure they work.

[WR269]

15 minutes ago, mmerelles said:

This behavior is a pretty solid evidence that you use a yoke/joystick which is sending noise spikes from the pitch potentiometer (thus affecting all vertical modes), when you try to engage any vertical mode plane refuses because it is receiving pitch input from the controller and the aircraft "thinks" you are manipulating the yoke to override and regain control.

This can be confirmed having a screen capture of the displays and annunciators, but being blind it is just an assumption. I am 99% sure this is the problem but please share a screen capture if this happens again and i can help you quite easy on  this.

 

Please don't get me wrong, I am not saying VNAV has no issues. It actually has and the devs have confirmed they will rework vnav, but sometimes having screen captures helps to understand other problems that we assume are all vnav or if it is vnan we can document them properly so when vnav testing comes we make sure they work.

I thought it was too.....but why would it only engage above F210 in the first place?  I still have the same hardware and the last 2 flights since 1.1 have been perfect. 

Anyway, hope it works....also, some people reported that the JAR Ground Handling plug in is still giving issues with the IXEG 1.1 so it is something to keep in mind.

 

[stolowski]

Ok, some facts from my side: when I'm saying I cannot engage VNAV, I mean VNAV button - it doesn't go green for even a fraction of a second. I can use LVL CHG and other vertical modes just fine, so I don't think my joystick is producing any unexpected inputs. And as I said, after several attempts at some point very high VNAV button finally goes green.

Now, I watched the beginning part of Jan's video about full FMS Flight up to the point when he engages VNAV... I couldn't spot anything critical that I could have missed. Then I wanted to create some screenshots showing the problem and this time I chose a completely different route, with flat terrain all the way down (EPWA - EPGD in Poland) - and guess what, VNAV engaged just fine on first attempt at around 2000 AGL!

So the route that has problem with engaging VNAV for me is LOWI MOGTI P66 KPT L856 ETOXU LSZH, taking off from RWY 26. SID is MOGTI2H, STAR is NEGRA1A with AMIKI transition. I tried this exact flight 5-6 times already with same effect every single time. I made yet another flight on this route, here are some screenshots - at 8660 ft, high above the ground. I keep pushing VNAV button, no effect.

Now, that yellow CWS P makes me curious, any idea what that means and if this is a sign of an issue?

 

 

Edited June 1, 2017 by stolowski

[Morten]

Stolowski, look at the PFD horizon.  To the right you see in yellow "CWS P".  Control Wheel Steering Pitch.  The aircraft is in CWS mode now, so you will not be able to activate other vertical modes. As mmerelles suggested. There are two ways you could have entered this mode

1. Accidentally bumped into your yoke while the AP was on

2. You hardware is sending signals "spiking" it should not.  Try increasing the NULL zone in the joystick settings in XP to prevent this from happening.

M

 

Edited June 1, 2017 by Morten

[mmerelles]

21 minutes ago, stolowski said:

Now, that yellow CWS P makes me curious, any idea what that means and if this is a sign of an issue?

 

That yellow CWS P mode on the annunciator means what i was speaking to @WR269, the aircraft entered Control Whel Steering Pitch mode becuase the pilot is manipulating pitch and overriding the systems. Off course you are probably not manipulating anything, this is your yoke/joystick potentiometer sending noise and the aircraft "thinks" you are trying to regain control. 

 

EDIT: @Morten was faster

 

Edited June 1, 2017 by mmerelles

[stolowski]

Thanks for the suggestions, but I'm not sure if this is explains the problem... I've verified with joystick setup utility that indeed it's indicating very tiny input from time to time when not moved, but I also made sure that CWS deadzone is large enough to accomodate that (a little input results in just a very tiny red bar in the CWS deadzone). I've also set pitch, roll and heading nullzones to 0.05 via datarefs.

Below is a screenshot from yet another attempt (also showing my CWS deadzone setup). I got CWS P on the annunciator again, but managed to "get rid of it" by disconnecting and then re-activating AP but still couldn't engage VNAV afterwards.

Edited June 1, 2017 by stolowski

[mmerelles]

If you are still going CWS mode time to time, please move the CWS nullzone slider all the way to the right (that is what i did on my saitek times and problem completely solved).

I am unsure if monitoring the red bar is an accurate measure, i doubt potentiometer spikes will be reflected there for being so minimal in time.

 

For the VNAV thing, there may be issues certainly. If you share all the details, origin/destination airport, route, sid, star, transitions, all perf init data, etc. to replicate your exact flight i can try it

[mfor]

Make sure that the altitude fields in the legs page are set.

I flew from SLLP to SPJC via  ELAKO6 ELAKO UA304 JUL UM415 REMUS DCT CEDRO CEDRO5 and the hight setting for ELAKO was blank and VNAV wouldn't engage. After setting the altitude for ELAKO it worked just fine.

[Litjan]

...and if all of that fails - just use FLCHG to climb! It doesn´t do anything different from VNAV, except that the pilot needs to set the MCP speed window to the speed specified on the CLB page (if you want to climb at that speed).

VNAV will get an overhaul in upcoming fixes, and it is likely that you are not doing anything wrong, but that there is a problem with the VNAV calculation (especially if you have altitude restrictions on your departure).

Jan

 

[BenAugust]

sometimes i also cannot engage the V/S mode...

[stolowski]

On 6/2/2017 at 1:54 PM, Litjan said:

...and if all of that fails - just use FLCHG to climb! It doesn´t do anything different from VNAV, except that the pilot needs to set the MCP speed window to the speed specified on the CLB page (if you want to climb at that speed).

VNAV will get an overhaul in upcoming fixes, and it is likely that you are not doing anything wrong, but that there is a problem with the VNAV calculation (especially if you have altitude restrictions on your departure).

Jan

 

Thank you Jan, that sounds reasonable.

Looking forward for VNAV revamp!

[WR269]

Found something interesting last night...sometimes the FMC dies not assign altitudes to waypoints, particularly the SIDs...if this is the case, VNAV will not engage until you either manually enter an altitude or select direct to a waypoint that is showing an altitude

Sent from my SM-G935F using Tapatalk

[mmerelles]

VNAV will not work without a valid vertical profile.

 

it is always quite important you review the entire legs page during preflight to make sure you have everything right.

 

Sometimes complex SIDs including multiple/combined altitude constrains, or even bugs on the navigraph database, may lead to a waypoint having 0 as the altitude constrain on the flight plan. This is not valid for VNAV to work, you edit those manually on the legs page and problem solved.

 

note: looking at the charts is also useful to anticipate potential problems, anytime you see on a SID or STAR a waypoint that has a double altitude constrain i.e. WAYPOINT cross "7000A & 9000B" the FMC will likely put on the legs page 9000A which is incorrect. So you edit those as well for a proper vertical calculation. This will be improved when VNAV is revised.

 

hope this helps

[stolowski]

VNAV will not work without a valid vertical profile.

 

it is always quite important you review the entire legs page during preflight to make sure you have everything right.

 

Sometimes complex SIDs including multiple/combined altitude constrains, or even bugs on the navigraph database, may lead to a waypoint having 0 as the altitude constrain on the flight plan. This is not valid for VNAV to work, you edit those manually on the legs page and problem solved.

 

note: looking at the charts is also useful to anticipate potential problems, anytime you see on a SID or STAR a waypoint that has a double altitude constrain i.e. WAYPOINT cross "7000A & 9000B" the FMC will likely put on the legs page 9000A which is incorrect. So you edit those as well for a proper vertical calculation. This will be improved when VNAV is revised.

 

hope this helps

Thanks for further suggestions.

Yes, I know restrictions sometimes may be missing in the navdata and need to be entered manually and I was doing that, removing zeros or missing ones with correct values. However I didn't pay attention to -above and -below restrictions, perhpaps they were incorrect as you say.

I've flown a few other routes since with no problems engaging VNAV, so I suspect there was something wrong witthat particular route indeed.