Unable to engage CMDA

[joolsd 10]

I had to hand fly up to FL130, and am unable to engage CMD/A, however I can engage CMD/B.

Even when trimmed and flying level on all modes. LNAV, Heading, etc etc.

 

As far as I can see everything is executed in the CDU. And there are no errors on the overhead.

I was wondering if it was to do with the Master option, IE the F/O or captain? I can't remember how to change this? But I might be doing something different. I have not seen this before?

 

I am not sure if it is a fail or just me forgetting something. I would love to know what it is before I land?

 

Thank you

 

Jools

[Budbud 227]

Hi,

 

This could be wrong but have you tried to switch off both FD and make sure you reselect the captain's one first? I have a doubt and I cannot check it now but maybe you can switch only the autopilot corresponding to the FD in control. (Left FD/CMD A - right FD/CMD B ).

[joolsd 10]

Hi,

 

This could be wrong but have you tried to switch off both FD and make sure you reselect the captain's one first? I have a doubt and I cannot check it now but maybe you can switch only the autopilot corresponding to the FD in control. (Left FD/CMD A - right FD/CMD B ).

 

I did try that, I saw the Captains side come on briefly (the green light). But still unable to select CMD/A.

[Budbud 227]

Do you mean that the captain's FD doesn't stay on?

What actually is the state of the FDs when you try to press the CMD A?

[joolsd 10]

Do you mean that the captain's FD doesn't stay on?

What actually is the state of the FDs when you try to press the CMD A?

 

The FD comes on but with no green master. The CMD/A will not switch on.

 

ON the PFD, LNAV/VNAV  with green CMD.

 

in Green, FMC SPD/LNAV/VNAV PTH

 

 

https://postimg.org/image/nyvotr099/

[Budbud 227]

I think you cannot select CMD A because the left FD is off. I guess that if you can select the CMD B it means that the right FD is on?

What happens on ground before takeoff when you select both FDs starting by the left one: does the left one briefly light up then the right stays lit?

 

Do you load the NG with a custom panel state?

[joolsd 10]

I think you cannot select CMD A because the left FD is off. I guess that if you can select the CMD B it means that the right FD is on?

What happens on ground before takeoff when you select both FDs starting by the left one: does the left one briefly light up then the right stays lit?

 

Do you load the NG with a custom panel state?

 

I loaded from 'Cold and Dark' on this occasion. I tried engaging the captains FD with the F/O F/D off as well.I tried many different, combinations.

MCP checks seemed normal, on the ground. It is had to say now that the flight is over, but you could be right, maybe something wasn't right.

 

I tried turning everything off at FL350. All the flight modes off one by one. CMD B off. All F/Ds off. Then doing as you say, putting the captains F/D on first then the F/O. The CMD A. (Unsuccessful) but CMD B does come on.

 

I managed to do an ILS into RWY34 at Zurich with just CMD B, without CMD/A agreement. CMD/A wouldn't work on the ILS anyway.

 

Can autopilots fail in this simulation or is it user error?

[ALF1 15]

Verify no system failures in system A. Can you alternate the master FD between the captain's and FO's ? You should be able to engage either command A or B and the master will switch over to the engaged system. Are you getting any FD indications on the captains's side regardless of autopilot engagement ? If you are, it is most likely a hydraulic system failure that you will have to fix from the CDU.

 

Edited: I saw the image you posted, you definitely have an active captain's FD, so your failure to engage the system A cmd is a failure the autopilot is broken. You have to check for failures in the CDU and fix it.

[joolsd 10]

Edited: I saw the image you posted, you definitely have an active captain's FD, so your failure to engage the system A cmd is a failure the autopilot is broken. You have to check for failures in the CDU and fix it.

 

Ok, that is interesting. I didn't set this up...so how can I go into the menu settings and do this on purpose?

[Budbud 227]

Have a look at the introduction manual and search for failures.

 

Also, if you don't find any active failure when you can set the CMD A, then try to load a flight with the default panel state to rule out any corrupted panel state issue.

[joolsd 10]

Have a look at the introduction manual and search for failures.

 

Also, if you don't find any active failure when you can set the CMD A, then try to load a flight with the default panel state to rule out any corrupted panel state issue.

 

Ok that sound interesting.

[Spin737 102]

Isn't this the issue with "realistic A/P engagement" or some such thing? If you move the yoke with the A/P on it breaks the override and the A/P won't engage. Check failures and read up on the A/P engagement options.

[joolsd 10]

Isn't this the issue with "realistic A/P engagement" or some such thing? If you move the yoke with the A/P on it breaks the override and the A/P won't engage. Check failures and read up on the A/P engagement options.

 

I read the section in question. I can only guess that I must of been trimming or pressing the trim button on my yoke at the same time. I am sure this has happend before, but not very offten.

I will only really know if I do another flight. And I could also do this from cold and dark and see what happens.

[ALF1 15]

If you are trimming then you could not engage CMD B either.

[joolsd 10]

If you are trimming then you could not engage CMD B either.

 

The CMD B was the only AP I could use, later on in the flight. And I did use it for most of the flight. As suggested earlier, it is to do with the 'realistic AP option', I wasn't attempting to use B after take off. So obviously I wasn't in trim enough or just pressed it again at the wrong time. User error.

 

It wasn't a corrupted panel state because I did another flight on the way back. LSZH-EGKK, a relatively smoother take off.

 

However, I did encounter a very strange SID out of LSZH which was the VIBIT 3S. 

 

https://postimg.org/image/pux2vw0br/

 

http://www.vacc.ch/en/airports_and_charts/

 

And the magenta line loops like this. I couldn't select LNAV on the ground only HDG,  so hand flew the loop until established on the R053. Then everything worked well. I aimed the HDG select (which did arm on the ground)  in the direction of the intercept course, just to save me time spinning the dial to the noise of the plane. I'm not sure of the correct technique for this SID but it worked for me.