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777 Pitch down and dive

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I was just wondering if there are any ways to fix these issues for me. My affinity mask is 5... and load is I think only 100% on my first core when landing. The freezing happens in both the NGX and 777 but only in highly dense areas. Virtual Memory was at ~2.9GB, and it's version 1.10.6320

 

Pitch: The airspeed increases and it starts gaining altitude whilst pitching down to keep on path. Is it just me being a noob?

 

Freeze: 

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I confess, that is a very unusual looking combination of pitch/power/airspeed!
 

I notice that there is a lot of turbulence going on, so I would suggest this is weather related: I can only assume that you were in a mammoth updraft. If you watch the instruments, at the start of the video the pitch & power looks normal. Then the VS starts increasing, so the A/P pitches down (correctly) to maintain altitude. At the same time the airspeed starts falling off rapidly -- which given the 10 degrees nose-down and 70% N1 is unusual!

 

As the aircraft comes out of the updraft the vertical speed and airspeed trends reverse and the aircraft begins to recover back to the VNAV path.

 

Not really sure what else the autopilot could have done to be honest: the aircraft started climbing, so it pitched down to correct.

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Not sure how the two look similar at all, if I'm honest. In the first video, the aircraft is quite happily maintaining 9000ft and 235kts, with the power around 75% N1. This looks normal.

 

The aircraft then starts climbing after the start of the video, so the autopilot pitches the nose down to compensate. The speed and thrust remains fairly constant.

 

From around 0.17, the aircraft's rate of climb increases despite the nose down inputs, so the autopilot applies further nose down. The speed also begins to drop, so the autothrust increases power to around 90% N1.

 

This situation continues: aircraft climbing, speed dropping. The autopilot applies thrust and more nose down to counteract. What else would you do?

 

At around 0.38 the V/S finally starts decreasing and the speed trend begins to reverse and start to increase. At this point the aircraft is now around 10 deg nose down and above the VNAV path. So the autopilot continues to hold the nose down to recapture the path and bring the speed back up. It then overshoots slightly, reduces the rate of decent and modulates the thrust to maintain 240kts.

 

Again, I'm not sure what you're expect the autopilot to do in this situation. It is pitching the nose down because the aircraft is gaining altitude due to some sort of outside influence -- i.e. the weather. If the aircraft starts unexpectedly gaining altitude and losing airspeed, how would you fix that as the pilot? Column forward and thrust levers forward. That's what the A/P is doing in your video. What behaviour were you expecting?

 

The early descent video that James links to is a completely different situation: smooth air, cruising level, an early descent commanded and the aircraft responds by pitching down in to the overspeed clacker. Clearly, there's something wrong there.

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Pitch: The airspeed increases and it starts gaining altitude whilst pitching down to keep on path. Is it just me being a noob?

I don't think having Flap 5 selected is helping with the negative pitch angle in the first video. I see later on flaps are retracted. If flap had been extended and speed reduced it might have gone better. Unlike the 737NG, the 777 will not schedule speed reduction with flap selection, you have to intervene youself. Also you are in turbulence and FSX is notorious for not responding well to AP or A/T speed errors in those conditions.

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Well it happens the moment after I put down flaps... so I was thinking it might have been caused by that. 

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The A/P starts diving in order to regain the lost speed, but it would just need 2-3000 ft/min *and* until the speed is again the scheduled one, then the airplane should increase pitch and resume normal rate of descent. What the PMDG 777 does in a buggy way is diving up to 10000 ft/min (without a reason) and then, of course, it has difficulties in recovering, thus reaching overspeed. I already submitted a ticket about that, but it looked like they were reluctant to aknowledge the bug... 

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I already submitted a ticket about that, but it looked like they were reluctant to aknowledge the bug...

 

I am not speaking for PMDG, but it you have a bug that is reproducible then in all likelihood it  was put into the bug tracking system. 

 

I've seen the 777 pitch commands respond slowly in VNAV to changing descent profiles and weather, but assume that the slow pitch changes are designed into the control laws of the system to reduce acceleration loads (G loads).  There are times when you have to fly the airplane by taking over from VNAV and using MCP SPD and V/S, in my opinion it seems realistic but I'm not T7 rated.

 

Are you T7 rated?

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Well it happens the moment after I put down flaps... so I was thinking it might have been caused by that. 

But a change in pitch and lift due to flap extension is to be expected. You need to reduce speed at the same time.

 

The A/P starts diving in order to regain the lost speed, but it would just need 2-3000 ft/min *and* until the speed is again the scheduled one, then the airplane should increase pitch and resume normal rate of descent. What the PMDG 777 does in a buggy way is diving up to 10000 ft/min (without a reason) and then, of course, it has difficulties in recovering, thus reaching overspeed. I already submitted a ticket about that, but it looked like they were reluctant to aknowledge the bug... 

If the speed doesn't respond to pitch then the AP will pitch down more to try and control it. The problem could well be the way turbulence is done in FSX and how it affects dynamics, not the 777 itself.

 

What you say makes no sense. If it doesn't recover the lost airspeed at 2-3000 ft/min down and increases to 10,000 ft/min how does it end up overspeeding? It must have passed through the target speed long before that and so started pitching up again.

 

If it was a design bug then we should all suffer from it. I haven't seen the 777 misbehaving like this myself. Maybe PMDG can't reproduce your problem and therefore haven't placed it on the list to be fixed.

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Well it happens the moment after I put down flaps... so I was thinking it might have been caused by that. 

But a change in pitch and lift due to flap extension is to be expected. You need to reduce speed at the same time.

 

Well obviously, yeah. There is no way this is normal behavior, I was just trying to resolve the issue. It would balloon up, not down though. Everyone who I've talked to never said they had the problem. I'm using ASN SP2b or whatever the latest is called if that helps..

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Nick,

 

I am convinced that your issue lies with Activesky. Check your settings, try reducing the maximum updraft/downdraft and maximum cloud/wind turbulence a little and see if you still get the problem.

 

As I say, the autopilot has not commanded a climb: quite the opposite, it is pitching down to counter an uncommanded climb that can only have come from a weather event. It continues to pitch down until the aircraft finally begins to descend, overshoots the VNAV path slightly and then pitches back up to stabilise the descent and regain the path.

 

Extending flaps will cause a balloon, but not to this extent: there are external influences at work here.

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What you say makes no sense. If it doesn't recover the lost airspeed at 2-3000 ft/min down and increases to 10,000 ft/min how does it end up overspeeding? It must have passed through the target speed long before that and so started pitching up again.

 

Unfortunately what I say makes sense, since the aircraft behaviour in this case is not correct. See the video I made, you can clearly see that the aircraft realizes that it has reached the target speed again much later than it should, and not recovering in time with that rate of descent (10000 fpm!) means going into overspeed. I did a lot of testing, even with zero wind, and I had it happening several times. Whatever, the real airplane will never go down with 10000 fpm!

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The A/P starts diving in order to regain the lost speed, but it would just need 2-3000 ft/min *and* until the speed is again the scheduled one, then the airplane should increase pitch and resume normal rate of descent. What the PMDG 777 does in a buggy way is diving up to 10000 ft/min (without a reason) and then, of course, it has difficulties in recovering, thus reaching overspeed. I already submitted a ticket about that, but it looked like they were reluctant to aknowledge the bug... 

 

well the reason is that you are entering throttle hold mode by commanding vnav descent some 20nm before the intended vertical profile, but the throttles stay at cruise thrust. they should be reduced significantly at this point, with letting the auto throttle handle it you will reduce to 250knots or so in a shallow dive and then it will tip over and follow the vnav path when you reach it eventually. maybe check that you aren't manually overriding the autothrottle if you aren't sure what it is trying to do for you. basically you're commanding that crazy dive and then wondering why it can't recover from it! on how the different throttle modes work (the clue is the changes on the FMA in front of you) it will hopefully make more sense if you read about it in the manual or check this thread which has a lot of info...http://forum.avsim.net/topic/445253-autothrottle-hold-mode/  .... i'm not an expert myself so i can't really explain it in full detail. i think you will find if you leave the altitude set to what you want without commanding a change then when you hit the t/d it will descend like you expect. alternatively if you must reduce altitude before the profile, then use v/s mode and set your speeds and descents where you want them (also look at the DES NOW command in the fmc)..

anyway cheers and good luck

-andy crosby

It's definitely something similar to that. Couldn't find another one diving, but it does happen quite frequently which is why I don't think it was an updraft.

 

And here is another freeze.

https://youtu.be/kSO5peHj9h8?t=1h57m34s

 

also to the original poster, did you try enabling the pre-loading of sounds, it is somewhere in the FMC menus (the install manuals have pretty specific info about this) but that was to solve the freezing that happens when it tries to load the landing sounds on touchdown. it will eat VAS as the tradeoff. i don't know what capture setup you are using but a problem like that could be exacerbated if you are for example recording to the same drive as your fsx install and by having stuff that is going on using a lot of file bandwidth already. just a suggestion!

cheers

-andy crosby

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Unfortunately what I say makes sense, since the aircraft behaviour in this case is not correct. See the video I made, you can clearly see that the aircraft realizes that it has reached the target speed again much later than it should, and not recovering in time with that rate of descent (10000 fpm!) means going into overspeed. I did a lot of testing, even with zero wind, and I had it happening several times. Whatever, the real airplane will never go down with 10000 fpm!

My 777 doesn't do what you describe or what your video shows. Descend Now results in a 1000 ft/min descent until the flight path meets the originally planned descent path.

 

Are you retarding your thrust levers to idle after commencing descent? This is recommended by PMDG due to the way A/T hold mode works in the sim. The only times I've had descent problems in the 777 I've forgotten to do this.

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That first video...with the totally insane pitch down attitude while still climbing is simply not possible.

 

Unless...

 

Unless you were caught in a severe thunderstorm, being sucked up in a 10.000ft/min updraft.

(something that sometimes realy ruins the day for glider pilots I am told)

 

So, this has nothing to do with FMC modes or Autopilot misbehavior.

 

It can only be a corrupt install or ASN in my opinion.

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Okay thanks everyone. I'll try out the sound fix for the freezing. VAS isn't an issue for me. I'll reinstall ASN and the 777 too. Does anyone want to suggest what maximum updraft/downdraft and maximum cloud/wind turbulence they use? Mine is just maxed out. I'll report back on Friday.

 

 


i don't know what capture setup you are using but a problem like that could be exacerbated if you are for example recording to the same drive as your fsx install and by having stuff that is going on using a lot of file bandwidth already. just a suggestion!

 

I use OBS to stream/capture which is on my other drive and it takes a lotttttt of bandwidth.

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I'll reinstall ASN and the 777 too. Does anyone want to suggest what maximum updraft/downdraft and maximum cloud/wind turbulence they use? Mine is just maxed out. I'll report back on Friday.

 

I don't think you need to reinstall ASN, just wind the sliders back. I'm not at home at the moment, but mine are around 30% from memory. Any more than that and even the lightest of chop results in being bounced around all over the shop with intermittent stick shaker activation -- certainly not realistic.

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Just watched the second video of the OP.

 

The freezes would support the thought of a corrupt install but to be honest it looks more like he is asking too much of his system.

 

As in high scenery load + high FSX settings? + PMDG complex aircraft + weather program = possible performance problems.

 

You need a well tuned high performance system to run all that at once!

 

To the OP:

What hardware (CPU/memory/GPU) do you have?

 

Try reducing FSX settings (especially AI Traffic puts a high load on FSX) and try not to use scenery and clouds with HD textures.

Also try reducing ASN settings so it reduces the load on your system (I dont use ASN, but from what I understand you can reduce the number of cloud layers, etc)

 

Anything you can think of that reduces the load FSX puts on your PC might help get rid of freezes and strange aircraft behavior (dive).

Your problems might all be caused by the system not being able to keep up with all the calculations.

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You can't be serious? Given the circumstances, most systems would run it as laggy as this. Everything I have is completely optimized... no ai. 1024 textures. 60nm cloud draw, cloud layers=4, vector disabled, other scenery disabled. I use a 3570k @4.2, 8 gigs of ddr3 gskill sniper series @1600 or so mhz idk off the top of my head...and a 1 gig 7850. It does just fine. Keep in mind that I was streaming and that dumbs down performance profoundly. It freezes like that regardless if I'm getting 45 or 5 fps and fsx never ooms either

 

Here it's smooth with no freezing. 

 

 

Smooth with freeze: (ignore the guy talking)

 

More smoothness:

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Have you run an adware/spyware scan on your PC lately?

 

I recall way back in the FS2000 days a chap saying that he had a similar issue -- generally smooth performance with micro freezes every now and then -- which cleared up after he ran an Adaware scan and got rid of a load of little pieces of junk that had accumulated.

 

Not guaranteeing this is the cause, but just a thought.

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Regarding the "nose down pitch" thing:

I would also say that there is some heavy (audible) updraft annoying your T7...

(IMO maybe "realistic" but more a kind of "maxed out force of nature dimension"; or just "normal weather" for your region of flying in terms of BEA AF447 report :blink:   Greetings go to "kevinh"...)

 

Regarding the "freezes":

your videos compare a daylight NGX approach into ENBR (Bergen/Norway) being fluid with a sunset T7 approach into EGLL (London Heathrow/UK) being temporarily freezing.

So there are three elements that make the comparison quite "problematic":

time of day (texture changes, GPU), aircraft flown (add-on complexity, CPU) and location used (scenery complexity, CPU+GPU).

In addition to that I always hear some "nice" tire squeaks (after your freezes) on touchdown.

Is it possible that there is an add-on running other soundfiles or something similar?

Trying default soundfiles (or even "better" the PMDG 22kHz versions) in combination with the already mentioned T7 FMC sound files preload option "ALL" (instead of "selective" or "off") could help here.

 

Always happy landings! B)

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