8 hours ago, LRBS said:

 

I also wish you had noticed when I mentioned" no wind conditions".

In the post I was responding to you didn’t say “no wind conditions”, you said “normal weather conditions” without specifying what you meant by that. I always use MS Live Weather, and in most of the flights I have done recently there has indeed been very little wind - surface or aloft. I flew from MIA to LAX yesterday at a cruise altitude of FL360 and the highest wind speed I saw at altitude was only 31 knots which agrees with the current high level wind charts across the southern US. It is much different at other times of the year of course, when high speed jet streams are more common.

But, that said, I simply do not see the same effects you do in LNAV - and I have specifically looked for them, watching the bank angle and flight director commands very carefully at a close zoom level on the PFD to see what the simulated AP is commanding. I have not (yet) seen the aircraft start a turn by rolling the wrong direction initially, nor have I seen constant bank angle changes in turns. I have seen those problems in the PMDG 737, but not the 777, but I will continue testing. If I do see those issues, I will certainly say so - I have no inclination to “whitewash” PMDG’s coding of the simulation, but if I see good performance I will certainly say so as well.

The only LNAV problem I consistently see is the abrupt “snap to level” in the very last part of a turn.

This somewhat mirrors what I have done I my “day job” I not only maintain autopilot systems on the ground, but have done flight test engineering: sitting in the jump seat with ARINC 429 databus readers connected to the AP command channels and analog or CANBUS decoders connected to the pitch and roll servo outputs of the autopilot to troubleshoot reported issues that only happen in flight. Typically, incorrect performance is caused by problems with the AP servos or associated cable connections to the control surfaces rather than any software errors in the AP/FD/FMS

As a pilot, you know how to fly the aircraft under AP control. As an avionics tech I know “how the sausage is made behind the scenes” so to speak.

I spoke of RF legs because they are somewhat unique in that they represent a specific path over the ground that the aircraft must follow. If there is a significant amount of wind, and the specific RF leg requires a directional change of 180 degrees or more, the bank angle will vary throughout the turn - it has to in order to track the path accurately. It doesn’t matter what kind of airplane one flies, either simulated or real, small or large.

Yes, in a zero wind situation or with very light winds, the turn will be conducted at a constant bank angle, or so close to one as to be “constant” for all intents and purposes. 

One of the r/w aircraft I currently work on is the CRJ-200. Although it is (sort of) capable of flying RF legs, it cannot do any procedure that requires adherence to RNP 0.17 limits (no RNP-AR) and the reason is that the Proline-4 autopilot cannot vary the bank angle in turns. It is only capable of turning at one of two fixed bank angles: 12.5 or 25 degrees.

 

 

 

 

 

1 hour ago, threexgreen said:

What's incorrect about it?

I use FLCH all the time, and it works perfectly, just like it is supposed to. 

4 hours ago, Bobsk8 said:

I spent two days touring the CAE Factory in Montreal Canada, years ago, when they were making the 767 Level D Sim that at the time cost around $25 million dollars. I remember them detailing how they got the flight info from Boeing Test Flights of the same aircraft, which cost them a couple of million dollars. Boeing even provided data from a few tested aircraft, so they could pick the average of the tested ones. 

Now, here some  are on Avsim, with a piece of $78 software on a PC that maybe is worth a bit over $1,000, expecting this software to fly exactly like the real aircraft. Talk about crazy......🤨

That’s a bit hyperbolic.

It’s far from being “exactly” like the real aircraft. Perhaps if you understood how the real Boeing AFDS operates you’d realise this. 
 

I don’t expect it to be exactly the same at all, but a bit more realistic, might make it more useful for real pilots to use. This is like the 737 lnav debates where you and other fans kept going on and on about how good it was and even now PMDG admit it needed updating and have improved it a bit on the 777 but there’s still a way to go. 
 

Edited July 15, 20241 yr by g-liner

45 minutes ago, Bobsk8 said:

I use FLCH all the time, and it works perfectly, just like it is supposed to. 

Have you used it in real life on many Boeings and if so which types? 

Edited July 15, 20241 yr by g-liner

2 hours ago, JRBarrett said:

In the post I was responding to you didn’t say “no wind conditions”, you said “normal weather conditions” without specifying what you meant by that. I always use MS Live Weather, and in most of the flights I have done recently there has indeed been very little wind - surface or aloft. I flew from MIA to LAX yesterday at a cruise altitude of FL360 and the highest wind speed I saw at altitude was only 31 knots which agrees with the current high level wind charts across the southern US. It is much different at other times of the year of course, when high speed jet streams are more common.

But, that said, I simply do not see the same effects you do in LNAV - and I have specifically looked for them, watching the bank angle and flight director commands very carefully at a close zoom level on the PFD to see what the simulated AP is commanding. I have not (yet) seen the aircraft start a turn by rolling the wrong direction initially, nor have I seen constant bank angle changes in turns. I have seen those problems in the PMDG 737, but not the 777, but I will continue testing. If I do see those issues, I will certainly say so - I have no inclination to “whitewash” PMDG’s coding of the simulation, but if I see good performance I will certainly say so as well.

The only LNAV problem I consistently see is the abrupt “snap to level” in the very last part of a turn.

This somewhat mirrors what I have done I my “day job” I not only maintain autopilot systems on the ground, but have done flight test engineering: sitting in the jump seat with ARINC 429 databus readers connected to the AP command channels and analog or CANBUS decoders connected to the pitch and roll servo outputs of the autopilot to troubleshoot reported issues that only happen in flight. Typically, incorrect performance is caused by problems with the AP servos or associated cable connections to the control surfaces rather than any software errors in the AP/FD/FMS

As a pilot, you know how to fly the aircraft under AP control. As an avionics tech I know “how the sausage is made behind the scenes” so to speak.

I spoke of RF legs because they are somewhat unique in that they represent a specific path over the ground that the aircraft must follow. If there is a significant amount of wind, and the specific RF leg requires a directional change of 180 degrees or more, the bank angle will vary throughout the turn - it has to in order to track the path accurately. It doesn’t matter what kind of airplane one flies, either simulated or real, small or large.

Yes, in a zero wind situation or with very light winds, the turn will be conducted at a constant bank angle, or so close to one as to be “constant” for all intents and purposes. 

One of the r/w aircraft I currently work on is the CRJ-200. Although it is (sort of) capable of flying RF legs, it cannot do any procedure that requires adherence to RNP 0.17 limits (no RNP-AR) and the reason is that the Proline-4 autopilot cannot vary the bank angle in turns. It is only capable of turning at one of two fixed bank angles: 12.5 or 25 degrees.

Just a quick correction: I meant to say "no wind conditions," but I wrote something else. My apologies.

 

When I think back, a few of us, the real pilots mentioned the obvious issues, and many people here said that the 737 is perfect in this respect; no issues can be observed. 

 

Now, almost the same people changed their tone: The 737 has issues. This time, the 777 doesn't have any problems that can be seen, exactly the same rhetoric as it was with the 737. 

 

Well, it's a complete waste of time. 

 

Let me be completely direct: both have issues in many aspects that many don't see, don't know, refuse to accept reality, and love to be argumentative.

 

When I criticized something, I wanted people to realize that this product could be improved and raised above the average compared to other developers. 

4 hours ago, g-liner said:

Have you used it in real life on many Boeings and if so which types? 

I was wondering what the issue is with FLCH. This is a genuine question out of curiosity.

18 hours ago, Bobsk8 said:

The post above was what I was trying to point out when I commented that someone had probably not worked in avionics, and for that I got blasted.  Oh well, that's Avsim in action. 😉

You were trying to point out all that by a single dismissive one-liner "I guess you never worked on Avionics"?

Well, then maybe try harder next time.

Btw., you got blasted for your attitude, not whether or not you were right. 

1 hour ago, threexgreen said:

I was wondering what the issue is with FLCH. This is a genuine question out of curiosity.

There was a few issues I saw with it Ibut one was it wouldn’t engage when level and the speed window then didn’t open when it should. 

Edited July 15, 20241 yr by g-liner

I'm using the 777 primarily to build custom procedures in the new PMDG navdata (which actually looks to be the standard Navigraph DFD format) so that I can move them over to the 73 database when that gets the navdata upgrade, and I've noticed something interesting.  In my testing, I've flown several RNP (AR) approaches in the 777 where I've seen strange flight guidance behavior, and also some that it handles better.  I've also seen this strange behavior on some of my work, and what I've learned is that I can eliminate it with tweaks to the navdata.

  For instance, the "snap to level" behavior that folks complain about - I don't see this at every waypoint transition, but where I have seen it, I've been able to reduce or eliminate it by altering the magnetic heading that defines the end of the segment (it often seems to be RF segments where this happens, and that's where I've fixed it).  This same parameter can control wing wagging behavior at a waypoint in the middle of an RF segment; the waypoints don't move, the magenta line doesn't move, but the AFDS behavior is changed.  I've got the RNVM26 into Juneau almost done, and the long arcing 180 degree RF segment into the Gastineau channel works perfectly - smooth roll in, rock solid all the way through the arc, smooth roll out to hit the exit waypoint and pick up the TF leg to the next fix.  

So, I'm starting to wonder if some of this behavior we've been critical of is due more to the values in the Navigraph data for some procedures?

This is an interesting discussion, but it's kinda going around in circles because the two groups of people (the actual 777 pilots and the rest of us) appreciate and understand the plane in two entirely different ways. 

The real pilots are talking about stuff that I barely understand, and even if I put in the googling to try and understand, I cannot really get it without actually going through pilot school! 

My nephew plays tennis at a high level, and is currently ranked #2 (under 18) in his country of birth (and ~600 worldwide), is on the junior Davis Cup team and so on.. I've played tennis for fun, and have watched tennis for 30+ years.. but when we watch a grand slam match together, it's like we watch entirely different matches. He notices and understands the game in a way that I simply cannot see, and even though he tries to explain it to me, I don't really get it the way he does. 

This discussion reminds me of that 😄

No offence intended to anyone, and I'm sure there are many people that are much smarter than I am that do fully understand what the pilots are saying.. but even so, the professionals approach the issue in what is clearly a different way to the amateurs. 

 

I have personally found exactly that to be fascinating about flight sim; it's just a video game, yes, but it's gotten so nuanced and detailed that we can actually HAVE these conversations.  That's pretty incredible, I think.

I've been enjoying 777 a lot; however, under certain circumstance I had the autopilot overbanked and disconnected. It happened twice to me and coincidentally both time with strong winds and turbulence. In one case I can write out due to strong turbulence, but in another case it was kind odd. The winds were around 20 kts (upwind) I was joining localizer and everything looks great, until autopilot started banking more and more until  "bank angle" siren and autopilot disengaged.  In both of those "incidents" I had take over and stabilize manually. In any case, it's not a show killer for me.

On 7/15/2024 at 6:53 PM, Stearmandriver said:

I'm using the 777 primarily to build custom procedures in the new PMDG navdata (which actually looks to be the standard Navigraph DFD format) so that I can move them over to the 73 database when that gets the navdata upgrade, and I've noticed something interesting.  In my testing, I've flown several RNP (AR) approaches in the 777 where I've seen strange flight guidance behavior, and also some that it handles better.  I've also seen this strange behavior on some of my work, and what I've learned is that I can eliminate it with tweaks to the navdata.

  For instance, the "snap to level" behavior that folks complain about - I don't see this at every waypoint transition, but where I have seen it, I've been able to reduce or eliminate it by altering the magnetic heading that defines the end of the segment (it often seems to be RF segments where this happens, and that's where I've fixed it).  This same parameter can control wing wagging behavior at a waypoint in the middle of an RF segment; the waypoints don't move, the magenta line doesn't move, but the AFDS behavior is changed.  I've got the RNVM26 into Juneau almost done, and the long arcing 180 degree RF segment into the Gastineau channel works perfectly - smooth roll in, rock solid all the way through the arc, smooth roll out to hit the exit waypoint and pick up the TF leg to the next fix.  

So, I'm starting to wonder if some of this behavior we've been critical of is due more to the values in the Navigraph data for some procedures?

How are you altering the magnetic heading in the database? Are you increasing it or decreasing it? Or does it depend on the particular segment?

Edited July 18, 20241 yr by RNAVV19R

6 hours ago, RNAVV19R said:

How are you altering the magnetic heading in the database? Are you increasing it or decreasing it? Or does it depend on the particular segment?

It depends on the segment, but generally changing it to be the same as the outbound heading from the upcoming waypoint helps.  In the navigraph data it's typically a couple degrees prior to the outbound heading from the next waypoint, and what I *think* is happening (I do not know this for sure) is that when the plane hits the magnetic heading, it switches into more of a TF or DF leg direct to the fix.  This happens almost at waypoint passage, so can manifest as a wing rock.

Apparently the recent 777 update tweaks some of this behavior though, so worth trying that before you make too many database edits.