Land 3 disconnecting

[RDG41 1]

Hi,

I have a problem that on short final LAND 3 disconnects and says not available. Initially it connects and lights up green. Is there a setting somewhere that I have turned on to disconnect LAND 3 automatically?

Thanks in advance,

Ron

[Mike777 163]

 

 

I have a problem that on short final LAND 3 disconnects and says not available. Initially it connects and lights up green. Is there a setting somewhere that I have turned on to disconnect LAND 3 automatically?

Thanks in advance,

 

Hi, Ron,

 

A couple of questions:

 

1) Is the autopilot disconnecting at the same time? 

 

2) Does this happen only at one runway or one airport, or at many?  Does it happen at FSX unmodified airports surrounded by unmodified scenery?

 

3) Could your joystick be sending spikes or could you be moving it inadvertently?

 

4) Are you closing down the PMDG 777 and then restarting from the last saved situation (including panel state)?

 

Mike

[Budbud 227]

Hello,

 

What do you mean by "no available"? Do you mean that you have no autoland on the  the PFD?

Can you describe the following:

_ type of approach

_ sequence of the modes on the FMA (SPD / LOC / GS, both ATs armed and active, both FDs on, AP on, FLARE / ROLLOUT armed...)

_ At what moment the LAND 3 transitions to NO AUTOLAND (if it is the message you have when you say "disconnects") and the situation when it happens (altitude and MCP/FMA state)

_ make sure that you have no failure active

 

If the AP disconnects, as Mikes says, chances are that your hardware sends spikes that force the AP to disco, which causes the LAND 3 to release as it is a mode for the autopilot.

Otherwise, if the AP stays engaged, then you either have a failure or the approach mode is not engages by 600ft AGL.

[RDG41 1]

Hi Mike/ Romain,

It seemed to just start doing it out of the blue. It also happened at any other airports I was trying to land at. It seemed to disconnect right at the set altimeter level at 2000ft. Auto throttle was still connected, L nav still connected but V nav not, as I had already engaged the approach button. The master warning would go off at this point in amber and the plane would just fly straight.

 

Now these were from loaded flights. They loaded correctly each time and I did load the panel state as well. I finally decided to reinstall the 777.  I also reinstalled the latest navdata and was able to autoland at the previous airport that I couldn't before. So it seems to have solved the issue. Thanks for replying.

 

[Budbud 227]

 

 

Auto throttle was still connected, L nav still connected but V nav not, as I had already engaged the approach button

 

Glad your problem is solved.
However for further reference, I guess you are talking about the MCP buttons lit/unlit? The only way to really know what the aircraft is doing is to check the FMA. 

I don't remember what are the LNAV and VNAV buttons states when I'm established on the ILS but I know that the FMA changes from LNAV/VNAV PTH to LOC/GS. I'll check next flight, however the config you describe seems a bit weird to me.

[RDG41 1]

That's correct. GS is established, LOC establishes correctly for me just as you described, and then the APR button is pressed. But I'm guessing that somehow the LOC was being lost just around when AUTOLAND3 would establish.

[Mike777 163]

 

 

That's correct. GS is established, LOC establishes correctly for me just as you described, and then the APR button is pressed. But I'm guessing that somehow the LOC was being lost just around when AUTOLAND3 would establish.

 

 

 

I don't remember what are the LNAV and VNAV buttons states when I'm established on the ILS but I know that the FMA changes from LNAV/VNAV PTH to LOC/GS. I'll check next flight, however the config you describe seems a bit weird to me.

 

Hi Ron and Romain,

 

Ron, I hope the issue is solved, but I'm a bit confused.  The Appr button would have to be pressed before either the LOC or the GS engage -- otherwise they will not.  Also, you said that the problem starts at 2000 feet, but that would be too soon for LAND 3 to light up (assuming you mean 2000 ft above ground level (AGL)). 

 

I just ran an approach starting in LNAV/VNAV and 1) LNAV light on the MCP goes off when LOC is engaged, 2) VNAV light on MCP goes off when GS engaged, and 3) LAND 3 engages just below 1500 ft AGL.   On the FMA, LNAV is green and LOC is white (armed) until LOC engages, similar behavior for VNAV & GS.

 

Also, I am wondering if your aircraft is configured so that it can begin to descend on the GS before the LOC is engaged, since you said " L nav still connected but V nav not, as I had already engaged the approach button."  Although frankly I don't see why having this configuration would cause the problems you are describing.

 

If you did not delete the saved flights and panel states before you reinstalled, I would be curious to know whether using them again causes issues.  Often a saved panel state (part  of a saved flight) can get corrupted and cause weird behavior.

 

Mike

[Budbud 227]

 

 

The Appr button would have to be pressed before either the LOC or the GS engage -- otherwise they will not.

 

If you press the LOC button, you can arm the LOC mode without GS. I guess it is what Ron did, then pressed the APP button to catch the glide but it's still not consistent with the LNAV going off before the VNAV button.

[RDG41 1]

 

 

The Appr button would have to be pressed before either the LOC or the GS engage

 

Not possible Mike. At least I have never been able to turn on the LOC button before the GS was picked up. And I have never been able to engage the APPR button until the aircraft was locked onto the Localizer. Once the APPR button is on, the VNAV light does go out.

[Budbud 227]

Ron,

 

It seems that our T7 don't work the same way! 

 

It is indeed possible to catch the glide slope before the localizer if you have this option enabled.

However, it is a rather unusual way to proceed with an ILS approach.

 

You normally either are vectored by ATC or guided by the STAR to a course which makes you intercept the localizer at an altitude below the glide slope. So whether you are in LNAV or HDG mode in any case you should be on course with APP armed (LOC and GS in white under the active roll and pitch modes on the FMA) and the LOC should kick in first and become active. Then when tracking the loc, you should see the GS become active when you intercept the glide. 

 

However, as I said, you can intercept the localizer before or even without the glide with LOC or APP armed but you cannot intercept the GS without the APP mode armed no matter what option is enabled. APP is the only mode that allows to follow the GS.

 

What could be possible though, if you set a lower altitude and the VNAV mode is active, and I guess it is what happens, it that the aircraft descents in VNAV PTH to follow the glide path (calculated glide, not the GS) and then if the LOC mode is armed, intercepts the loc. But in this case, you are on a hybrid LOC/VNAV PTH approach instead of full ILS (LOC/GS) approach.

 

Maybe you are too high on your approach to catch the glide?

[Mike777 163]

Romain said:

If you press the LOC button, you can arm the LOC mode without GS. I guess it is what Ron did, then pressed the APP button to catch the glide but it's still not consistent with the LNAV going off before the VNAV button.

 

-----------

 

Me:

Yes, of course you are quite correct.  I was assuming that we were only talking about pressing APPR while in LNAV/VNAV, and not using the LOC button at all.  I could have been clearer.

-----------

 

 

Romain:

You normally either are vectored by ATC or guided by the STAR to a course which makes you intercept the localizer at an altitude below the glide slope. So whether you are in LNAV or HDG mode in any case you should be on course with APP armed (LOC and GS in white under the active roll and pitch modes on the FMA) and the LOC should kick in first and become active. Then when tracking the loc, you should see the GS become active when you intercept the glide.

However, as I said, you can intercept the localizer before or even without the glide with LOC or APP armed but you cannot intercept the GS without the APP mode armed no matter what option is enabled. APP is the only mode that allows to follow the GS. [Mike's emphasis added]

What could be possible though, if you set a lower altitude and the VNAV mode is active, and I guess it is what happens, it that the aircraft descents in VNAV PTH to follow the glide path (calculated glide, not the GS) and then if the LOC mode is armed, intercepts the loc. But in this case, you are on a hybrid LOC/VNAV PTH approach instead of full ILS (LOC/GS) approach.

Maybe you are too high on your approach to catch the glide?

------------

Me:

I agree 100%.

 

------------

Ron said:
Not possible Mike. At least I have never been able to turn on the LOC button before the GS was picked up. And I have never been able to engage the APPR button until the aircraft was locked onto the Localizer. Once the APPR button is on, the VNAV light does go out.

------------

 

Me:

I usually just press APPR and, as Romain said, first the localizer is locked in and then the GS.  I press APPR all the time before I am on either the localizer path or the GS.  But it is certainly possible to press just LOC, in which case the aircraft will remain in its previous horizontal mode (LNAV, or Heading Select, or Heading Hold) until it is close to the horizontal localizer path, when it will switch to LOC on the FMA and follow the horizontal localizer path.
 

Perhaps there  is a confusion of terminology here?  It is true that you can't press LOC or APPR until localizer or GS signals are detected -- for example if you are a hundred miles away I don't think LOC or APPR will engage (turn green on MCP) because the aircraft is too far away to detect any runway localizer or GS signals (even if the correct frequency is tuned).  But once the localizer is detected -- showing on the MFD in Approach mode or on the PFD, you can certainly press LOC on the MCP and have it turn green.  Same for detection of the GS signal.

 

Mike

[RDG41 1]

Guess I've always followed the tutorial which is to engage the LOC then the APP button. Never knew I could bypass the LOC button and go straight to the APP once on the glide path. I learned something new, thanks :smile:  I'll try this next time. You guys both sound like you know a lot more than I do on the 777. Once I followed the tutorial and landed successfully on auto land, I was happy and have flown the same way since. But I will try it your way and see how it goes.

[Mike777 163]

Guess I've always followed the tutorial which is to engage the LOC then the APP button. Never knew I could bypass the LOC button and go straight to the APP once on the glide path.

 

Glad to be of help.

 

Looking at p. 93 of Tutorial 1, I think the point is that you don't want to engage GS before you engage the localizer. So by only pressing LOC you prevent this from happening.   As Romain mentioned, some 777s are configured so that you can descend on the GS before you lock onto the localizer.  But it is dangerous.  The ILS path does not take into account obstacles that are far to the left or right of the approach path, so if you start to descend before you are lined up on the localizer, you could hit an obstacle.   However most 777s are set up so that they won't descend on the GS until they are on the localizer; so for them there is no risk in just pushing APPR.  You can check this setting for each specific aircraft on any CDU, Menu>PMDG Setup>Aircraft>Equipment.  On mine it is the very first item that pops up.

 

The other point Ryan (the author) makes is that if you are far out, your aircraft's nav radios won't detect the GS but will detect the localizer.  However I'm pretty sure that if you just press APPR, the aircraft will line up on the localizer path and keep following it until the GS is detected.

 

I also want to mention:

1) Kyle Rodgers has posted a video to accompany Tutorial #1 here:

http://www.avsim.com/topic/418246-tutorial-video-tutorial-1/

 

2) Tutorial #1.5 is available on this page, second item down:

http://www.precisionmanuals.com/pages/downloads/docs.html

 

Mike