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FDX016 - Nick

Keeping speed in heavy turbulence...

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Greetings,

 

I've been enjoying the heck out of the 777 since it was released, and just about flying the wings off her! However, this week I have come across some odd behavior while operating into and out of Keflavik, Iceland. I've included both cases below:

 

Scenario 1: Keflavik Approach and landing last night.

 

I did my usual flight from Moncton to Keflavik in the 777 for the first time last night (usually in an MD-11). The weather at Keflavik was nasty and they were experiencing very bad storms at the time. Winds were gusting up into the high 20's and peaking in the 30's. (This is why I like flying up there) So I knew I was in for an interesting approach and landing. I descended as I always have, and it was fairly uneventful until I got closer and lower to the field. As I got closer, I started having really bad turbulence, but it was nothing I haven't had before in a plane of this size. VNAV commanded 250 as I approached 10,000ft and I was surprised at how difficult it was for the plane to do this. It seemed like with every gust of wind, the autopilot would freak out and think that it was going to decelerate past 250 (even though I was still at 280) and adjust pitch to compensate. I ended up switching to VS and extending spoilers to slow down until I got slow enough to extend slats. After that it seemed to be fine going back to VNAV. Now for the approach- I decided to do a visual for RW20 and I descended to 3000 for the downwind. I leveled out and set speed to 220 to begin to slow and extend flaps. (Note that I'm still in pretty bad turbulence) I was surprised when the autothrottle began the same behavior as the autopilot did before, and began looping increase and decrease of thrust while never actually slowing down. I ended up commanding 180 and still it never left 250. In fact, it began to accelerate slowly and I ended up disconnecting autothrottle, pulling the thrust levers back to idle, and allowing the plane to slow while extending flaps. Turning final, I reengaged autothrottle to see how it would cope, lowered gear, and the last notch or two of flaps. Speed was commanded at VREF +5, but to my surprise it started chasing the speed again and allowing a gradual increase of speed. I ended up going around (which worked flawlessly I might add) and tried again. By the time I got back around for the downwind the wind was still strong but not gusting as bad and I made a much more normal approach and landing.

 

Scenario 2: Keflavik Departure, about 30 minutes ago.

 

I do my usual preflight, startup, taxi-out, and takeoff as normal. Winds were 200, at 15-18 gusting to 25. After the climbout, I engage autopilot, VNAV, and HDG SEL to turn towards my course. I noticed it was taking longer than usual for the seed to increase past my retract speed... It was like deja vu all over again, except this time it was that the plane was hesitant to accelerate. With every bump, the pitch would fluctuate and it never gained any speed, and in fact started to decelerate to the point where I pressed altitude hold and waited to get past my retract speed before re-engaging VNAV. I went now and set LNAV and we were on our way. At this point I was perplexed, so I got up to get a nice Cherry Coke and think about why it was doing this. Upon returning to my chair, I see that I am at about 14,000 feet and down around the stick shaker. I went into VS mode, set 2000fpm, and waited. To my surprise, now the autothrottle is fluctuating and I ended up leveling off to gain enough speed where I felt safe enough to continue the climb. I engage VNAV, and watch as it does the same thing- pitching in the turbulence but never gaining speed. I actually got up to FL230 before the turbulence started to die off and everything went back to normal. The rest of the climb to FL350 was uneventful.

 

 

Phew- that was long. I tried to describe in detail what exactly I, and my little friend, did in order to see if anyone could pinpoint if it's my fault, a fault of the aircraft, or if I am just expecting too much of the autoflight system in turbulence. I was just surprised because I have encountered the same severity in other aircraft, such as the 737 and MD11, and they never had a problem like this. Anyone else having something similar? Or have any suggestions?

 

I'm also wondering if this falls under the "FBW tweaks and review" which is still on the Progress list in the SP1 fixes thread.

 

Thanks in advanced!

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Hi there,

 

Good descriptions and good handling I'd like to add :-)

 

It does not look like you are at fault from how you described things.

 

From the PMDG guide:

In FSX settings:

"We recommend that all users click the “Disable turbulence and thermal effects on aircraft”

(PMDG uses its own turbulence behavior)

 

FSUIPC can be a cause if you are using it.

Maybe you have activated some wind smoothing functions in FSUIPC that the PMDG777 does not like. FSUIPC is not recommended by PMDG, so try without any of those options.

Also make sure you use the latest FSUIPC version and delete the FSUIPC.ini (it will rebuild a new fresh one at FSX boot, but all joystick settings will be lost). Deleting the FSUIPC.ini file has fixed all kinds of problems!

 

Are you using a weather engine like REX, Active sky or OPUS?

Try deactivating them if you run into such problems again and see if that stops the behavior. And also try without turbulence options of such weather engines.

 

It could also be a typical screw up from FSX or the 777 for no apparent reason that never happens again.

Did you shut down and reboot FSX inbetween your two flights.

If not then that could support that thought.

I dont like saving flights and continuing from there. It is safer to just treat each flight as a new one. So reboot, create a new flight, choose the desired panel state (just not cold and dark as that causes all kinds of problems untill SP1 is realeased!) and then start the flight.

This prevents software errors from accumulating!

 

Can you reproduce those problems by just selecting FSX stormy weather, or by setting strong winds/gusts manually? If so then I can try here as well.

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It's common IRL for crews to disconnect all automatics in heavy turbulence.. Especially during approach/landing. It takes more of a human touch to navigate through the bumps.

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It might be common practise to 'go manual' during heavy turbulence, but totally disconnecting the autothrottles in a 777, as far as I know, only happens if there is a systems failure as per most airlines SOP.

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It might be common practise to 'go manual' during heavy turbulence, but totally disconnecting the autothrottles in a 777, as far as I know, only happens if there is a systems failure as per most airlines SOP.

SOP is this to keep the A/T on if it is doing its job. In heavy turbulence and gusts it is perfectly acceptable to disconnect the A/T if it is not performing.

 

As High flyer rightly states, disconect the automatics and fly the aircraft.

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This has nothing to do with FSX. The autothrottle of the 777 simply doesn't know how to deal with these conditions. The NGX does just fine in turbulence for me. But in the 777, I sometimes run into trouble.

 

Sent from my GT-I9300 using Tapatalk

 

 

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I have noticed that during VNAV decent that the auto-throttle often keeps spooling the engines up despite the IAS being above the commanded speed. I have also noticed that the vertical speed often hunts, sometimes at alarming rates, to maintain the VNAV descent path and that's with no turbulence and benign wind conditions. In fact I find it difficult to use VNAV descent to get to the right altitude for a successful approach, whereas, as Arjen stated, I don't have this problem with the NGX.

 

Regards

 

Andrew

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Thanks for the replies guys-

 

I'd like to add that I am using Active Sky 2012 and have been since it was released, and I am using a FSX cfg as well as a FSUIPC INI that is tweaked as per the AS2012 manual. So far it has been flawless. I'd also like to echo that it only happens in the 777. I don't have such an issue with the 737 or MD11.

 

I'm totally fine with disconnecting the automatics, but I am interested to see if anything is tweaked with SP1. I tend to believe the speed hunting is abnormal, but I can't say for sure.

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Very occasionally I have seen the funky behaviour of ActiveSky 2012/FSX sim connect/FSUICP and/or a flaky internet connection cause the wind to get in a circle motion at a high level wind speed.

 

Ie passing 500ft, seeing the windspeed pegged at 65 knots and the wind direction doing full 360 degree circles at a rate of about 1 every 2 seconds. Only going around and closing ActiveSky 2012 and reopening it (to let it find Simconnect again) will fix this.

 

It happens more often if my internet connection drops out during the flight.

 

If your airline SOP is never disconnect automation even if it isn't managing to prevent you from stalling and/or crashing, then refer them to the Asiana 214 crash investigation findings that were released on the 12th of December 2013.

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Very occasionally I have seen the funky behaviour of ActiveSky 2012/FSX sim connect/FSUICP and/or a flaky internet connection cause the wind to get in a circle motion at a high level wind speed.

 

Ie passing 500ft, seeing the windspeed pegged at 65 knots and the wind direction doing full 360 degree circles at a rate of about 1 every 2 seconds. Only going around and closing ActiveSky 2012 and reopening it (to let it find Simconnect again) will fix this.

 

It happens more often if my internet connection drops out during the flight.

 

If your airline SOP is never disconnect automation even if it isn't managing to prevent you from stalling and/or crashing, then refer them to the Asiana 214 crash investigation findings that were released on the 12th of December 2013.

Trent-

 

I have also noticed the winds changing in the manner that you describe, however it was not the case in the scenarios I'm talking about. The wind was steadily gusting... That's an oxymoron, isn't it haha  :blink:

 

About the SOP- We don't have an SOP detailing aircraft operation as such. I'm certainly not a button pusher nor do I rely solely on the automatics, but simply curious about something that I thought would be a normal situation for the airplane to handle and it handled it not-so-normally.

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Hello

 

I use REX Essential + OD, with turbulence effects turned off in FSX. 

 

I do remember a bug in an earlier version of AccuFeel where, when the clear-air turbulence slider was activated, it caused the AXE A320 to nosedive during descent and vertical speed to go crazy at times, but this has since been fixed and I've been using it without problems. Does anyone else use it? As others have experienced I don't get any problems with other add-on planes.

 

Andrew

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I have the exact same problem landing in any storm. exactly as OP described. have turbulance disabled. Using fsx default real world weather. if i change to clear skies, its fine. any fixes yet?

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I use ASN and have not had any issues with this.

 

By the way, disengaging the autothrottle is different to switching the autothrottle arm switch to off on the MCP.

 

Pressing the autothrottle disconnect button on the throttles is fine, because the stall protection features still activate when necessary.

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If turbulence gets bad enough, you'll have to kill the automatics (AT mainly).  Everything has limits.  It's not going to magically save you in all cases.

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Maybe you have activated some wind smoothing functions in FSUIPC that the PMDG777 does not like. FSUIPC is not recommended by PMDG, so try without any of those options.

 

I use FSUIPC wind/pressure smoothing with all PMDG products with no problem. PMDG has not said don't use FSUIPC, they've actually offered tips on how to use it and specified one use not recommended (all contained in B777 Intro, e.g., pg 0.00.36)

 

See AP/AT TURB MODE TRIGGER in Intro pg 0.00.94 for a nifty feature that came out in B777 SP1.

 

Finally in my opinion, FSX cannot/does not/will never model turbulence or wind shifts or mircrobursts with any fidelity. I turn it off and live with the fact that this challenging part of flight simming cannot be simulated. Like I said, my opinion.

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I use FSUIPC wind/pressure smoothing with all PMDG products with no problem. PMDG has not said don't use FSUIPC, they've actually offered tips on how to use it and specified one use not recommended (all contained in B777 Intro, e.g., pg 0.00.36)

 

See AP/AT TURB MODE TRIGGER in Intro pg 0.00.94 for a nifty feature that came out in B777 SP1.

 

Finally in my opinion, FSX cannot/does not/will never model turbulence or wind shifts or mircrobursts with any fidelity. I turn it off and live with the fact that this challenging part of flight simming cannot be simulated. Like I said, my opinion.

You just corrected a reply of mine from december 2013!

 

I also do not use turbulence in FSX (unticked in the FSX settings).....it causes more problems than it is worth I think.

And I also use FSUIPC for all kinds of things all the time (home build throttle/brake pedals/buttons and key strokes/lua script for VAS plotting).....not for wind and pressure smoothing though because OPUS FSX weather engine already takes care of that.

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You just corrected a reply of mine from december 2013!

 

Wow, I did not notice that.. I usually check the post vintage but missed it this time. Sorry.

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Wow, I did not notice that.. I usually check the post vintage but missed it this time. Sorry.

:-) happens to the best ;-)

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What does PMDG do to replicate the turbulence if its unchecked in FSX?

 

PMDG doesn't do anything.  They model aircraft, not weather.

 

Weather add-on developers, on the other hand, might do something to simulate turbulence (which ASN does).

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