Autothrust Extremely Slow to React on Approach

[markjj 47]

Eh, bad news.  It happened again.  At this point the AT's lack of response seems kind of unpredictable.  I flew a few flights where it maintained speed beautifully, but it just did the same thing again in which I was slowing to my final approach speed of 142 (down from 160 as requested by ATC), fully configured.  As I was approaching 142, the AT did nothing.  I waited and waited (for experimental purposes), and only at around 130 did it kick in ever so slightly.  I disengaged AT and manually got myself to 142, reengaged AT, and it seemed to be able to maintain it after that.  Thus, it's ability to maintain speed is utterly unpredictable, and it does not seem to be weather related (again, AT just refused to do anything until it was well below 10 knots of the command speed.  Realistically, it should start compensating before command speed is reached on the decel).  Another interesting thing occurred.  On this flight, I had no green acceleration arrow on the speed tape until touchdown (nothing on takeoff or flight).  

[PMDG777 231]

1 minute ago, markjj said:

Eh, bad news.  It happened again.  At this point the AT's lack of response seems kind of unpredictable.  I flew a few flights where it maintained speed beautifully, but it just did the same thing again in which I was slowing to my final approach speed of 142 (down from 160 as requested by ATC), fully configured.  As I was approaching 142, the AT did nothing.  I waited and waited (for experimental purposes), and only at around 130 did it kick in ever so slightly.  I disengaged AT and manually got myself to 142, reengaged AT, and it seemed to be able to maintain it after that.  Thus, it's ability to maintain speed is utterly unpredictable, and it does not seem to be weather related (again, AT just refused to do anything until it was well below 10 knots of the command speed.  Realistically, it should start compensating before command speed is reached on the decel).  Another interesting thing occurred.  On this flight, I had no green acceleration arrow on the speed tape until touchdown (nothing on takeoff or flight).  

You never responded to my last advice so I'll ask again. Does it occur with no weather engine running? Can you also remove any throttles/joysticks etc? Can you check to make sure you don't have a crossed key assignment for disengaging autothrottle?

[markjj 47]

13 minutes ago, PMDG777 said:

You never responded to my last advice so I'll ask again. Does it occur with no weather engine running? Can you also remove any throttles/joysticks etc? Can you check to make sure you don't have a crossed key assignment for disengaging autothrottle?

Thanks for the reply.  This occurs while running Active Sky 2016; however, the weather conditions do not seem to matter (ie, storms, clear skies, no wind, etc.).  Keep in mind that Prepar3d's turbulence checkbox is disabled as well.  I tried recalibrating my thrust levers (did not try without) and have ensured that nothing is disengaging AT.  However, the AT issue seems to happen randomly and it does not seem to be a hardware issue as it is entirely the result of the AT simply failing to initiate a response to the speed dip in time (AT was not in hold mode either, so the position of my thrust levers wouldn't matter).  Also, the weather does not seem to make a difference.  I will point out that it seems to maintain speed fine all the way up until full configuration.  It just seems to have trouble with the last portion of the approach when it is decelerating to final approach speed...it doesn't "catch" the command SPD

[markjj 47]

12 minutes ago, PMDG777 said:

You never responded to my last advice so I'll ask again. Does it occur with no weather engine running? Can you also remove any throttles/joysticks etc? Can you check to make sure you don't have a crossed key assignment for disengaging autothrottle?

I will try your advice and see what happens...will report back

[markjj 47]

So I followed the advice and I think I can safely say that this seems to be weather related.  Despite the fact that it occurs in more than one condition, it seems to happen particularly when there's moderate chop and/or windshear that affects the airspeed.  When I do encounter the problem, however, it seems to help if I incrementally lower the command speed, so that if it does fail to "catch" the set speed, it happens at a higher command speed and thus prevents me from falling below approach speed.

[PMDG777 231]

15 minutes ago, markjj said:

So I followed the advice and I think I can safely say that this seems to be weather related.  Despite the fact that it occurs in more than one condition, it seems to happen particularly when there's moderate chop and/or windshear that affects the airspeed.  When I do encounter the problem, however, it seems to help if I incrementally lower the command speed, so that if it does fail to "catch" the set speed, it happens at a higher command speed and thus prevents me from falling below approach speed.

And what happens if you run the sim without Active Sky? I've been trying to get you to do this for a while.

[downscc 1,327]

11 hours ago, markjj said:

I can safely say that this seems to be weather related.

Good to hear you are getting a grip on this.  My experience with any the HiFi weather engines is to dial back all the wind and gust factors to about 20 from default 100.  You can play with it to suit your preference but you have to dial them back from default.

[markjj 47]

23 hours ago, PMDG777 said:

And what happens if you run the sim without Active Sky? I've been trying to get you to do this for a while.

Without active sky, the issue only occurs if there is significant turbulence and/or wind shifts. Thus I don't think it's weather engine related, but rather the PMDG 777's response to excessive (and perhaps unrealistic) weather conditions. Like I said though, if I incrementally lower the command speed, it seems to maintain the approach speed rather well irrespective of weather engine or conditions, given that slowly lowering the speed allows the AT to catch up if it dips 

[markjj 47]

12 hours ago, downscc said:

Good to hear you are getting a grip on this.  My experience with any the HiFi weather engines is to dial back all the wind and gust factors to about 20 from default 100.  You can play with it to suit your preference but you have to dial them back from default.

It seems so. It's a bit of a shame given that it is quite fun to see the IAS fluctuate in gusty conditions, but everything has a price. As I said, incrementally lowering the command speed seems to be a "workaround". For example, if I set the command speed to 160 when my approach speed should be 142, any dip that results from excessive wind shifts will result in the plane merely dipping below 160, then allowing me to set the speed to 142 so that it can lock on more easily. Sounds tedious but in practice it's actually rather simple :). Also, this only seems to be an issue in gusty or very turbulent conditions, so most of the time it's no issue (keep in mind that for this to remain true, you must disable turbulence through Prepar3d's menu, as active sky will supply its own)

[downscc 1,327]

9 hours ago, markjj said:

It's a bit of a shame given that it is quite fun to see the IAS fluctuate in gusty conditions

Oh I agree, all my RW flying starts and ends in a place where it's normal to see 13028G42.  I can't land without wind.  However, the simulator is to blame and HiFi is doing their best to make it work.