Nasty weather and Autothrottle woes

[evaamo 549]

I flew the 777F from KMEM to LFPG today and the destination weather was just awful. ATIS (ActiveSky Next) warned about windshear in the vicinity, very close to Charles De Gaulle 27R, which I was using for landing.

 

The airplane was shaking like if it was a 172, but I continued my ILS approach manually, with A/T on SPD mode fighting to maintain 170kts until 7 miles out or so. Wind was from 300 at 9kts gusting to 20kts, and ASN was throwing heavy up and down drafts and after setting VRef (137kts) + 5 on the MCP and selecting flaps 30, the autothrottle started to have difficulties maintaining the commanded airspeed. At all times I was particularly careful of not falling victim to the known A/T mode traps, and I made sure we were at SPD mode the whole time.

 

As the aircraft was descending from 3000 to 1000ft, I hit a nasty downdraft and had to pull the yoke to maintain my otherwise "stable" approach. The engines were at 47 to 55% N1 and as I recovered the vertical speed (the nose was close to 15 degrees) the A/T let the speed drop below 130 knots and I entered into a stall (there was no windshear alert at any time). I quickly pushed TO/GA,retracted the gear and lowered the nose to reduce the AoA and gain some airspeed. It was a very very close call, as the aircraft started to descend due to the momentarily stall at between 1800 to 2300 fpm. I managed to recover the aircraft at 800-900ft AGL or so, and when the speed started to pick up and the turbulence allowed, I managed to fly the missed approach safely.

 

Remaining fuel was close to 8.5 tonnes, and the alternate airports in France didn't look much better. So this being a virtual situation and not the real deal, I programmed my approach in the FMC and went at it again. This time I made a longer approach (3 to 4nm longer) and tried to be much more careful at managing the airspeed and the descent. I hand flew the entire approach right after the LOC went alive, and a pair of miles short of G/S capture I threw down the gear and the flaps in order to have the A/T put the engines on a high N1 setting from early on. I suffered the same up/downdrafts this time although less acute, but still the A/T let the aircraft go below Vapp a few times, so I decided to set Vref+15-18kts on the MCP and closely monitor the airspeed / engine spool situation very closely. At 1000ft AGL I was a bit fast but in a stable approach nonetheless, and the turbulence made tense moments out of the rest of the final approach as the vertical speed and the airspeed suffered spikes. Touchdown was at Vref+5-7kts and the flare nearly at 10 degrees nose-up, which had me worried about a tail-strike.

 

I have a Logitech 3D Pro joystick but I don't use its throttle lever, I usually manage the speed using the keyboard. Not so sure I'll keep doing it this way after today, as I would definitely have preferred to manually control the throttles when the A/T accuracy started to suffer.

 

Anyway, in the end this nightmarish story came to a happy ending, but I would definitely like to hear from you T7 commanders about any recommendation or similar stories to better handle the aircraft in such situations.

 

If anyone at PMDG reads this: do you think modifying the default value in the new "turbulence filter" would have helped the A/T do a better job keeping the airspeed? Did you guys ever tried to put the aircraft and its A/T in such turbulent scenarios on the Level-D simulator you used? What was the outcome? What would be a realistic setting for ActiveSky Next turbulence in order to avoid compromising the correct behavior of the PMDG 777 and its systems?

 

I understand the best option would have been to avoid such weather, but you never know ;-)

 

Thanks so much for reading!

cheers

-E

[HighFlyer310 21]

Bottom line.. The autopilot/throttle has limitations. If your in unstable/turbulent air, the automatics are going to struggle because they are trying to chase their set values. I would recommend going out and buying a good hardware throttle (I use saitek x52 pro).. Either that or reduce your sliders in active sky. It is very common IRL for crews to disconnect the automatics when the going gets rough.. They simply can't keep up, which PMDG has modeled very well IMO.

[evaamo 549]

Hi Tom, evidently I've never flown the 777 and that's why, even when I think PMDG has modeled these constraints properly (I've been involved in software for UAV autopilots in the past), I think posting my story would be a good starting discussion to understand how other simmers (or even PMDG staff that had access to the Level-D) manage this aircraft in scenarios such as the one I described in my post.

 

I understand A/T is often disengaged in other types when certain conditions are met or even to completely hand fly that particular type, but as the 777 was designed to have the A/T engaged during all stages of a flight, would be great to know how often it really is disengaged when hitting bad weather.

 

On the other hand, I'm kind of surprised no windshear warning was displayed during the first approach.

 

Thanks about the throttle hardware recommendation, I prefer that option than dealing with Active Sky settings as I wouldn't know what setting is "real". I have flown in bad weather as a passenger and in Cessna's as a student, but have never felt anything like what Active Sky Next throws at my aircraft sometimes ;-)

 

cheers

-E

[777 340]

Autopilot and Auto throttle have their limitations, your flight reminds me of my thundery approach into EGBB, the AP was connected and did its job just about. Which makes you think in RL would pilots continue the approach in WX like that or divert to alt?

[Slayer 190]

I think VREF + 5 is not a set in stone rule. If there is a lot of wind then you need to account for that. I vaguely recall this discussion before and someone was kind enough to provide a link in one of the manuals with a more in depth breakdown of this same subject. Also keep in mind that the weather report may not reflect the actual conditions at all points around the airport, especially a large airport like that.

[HighFlyer310 21]

I myself have no experience in a leveld sim or the real thing. I do know a few airline guys, one who flies the 777. They all say that the autothrottle comes off on approach during turbulent conditions. I should say disconnected, but still armed in the event TOGA thrust is needed. The difference between RL and sim is that in RL, even with the autothrottles engaged, the PF still has authority over the thrust, the servos won't fight manual control. I'm not exactly a manual junkie but I'm sure that there is something in the FCOM that covers autothrottle ops in turbulent air. If not I'm sure that's left up to airline SOP. The trick is to keep "throttle jockeying" to a minimum during approach in any conditions. Large changes In thrust upset stability and ultimately creates more work on the controls than is necessary. I usually disconnect a/p and a/t at about 2500'.. Configure flaps/gear and find a sweet spot for thrust, from there it's only small changes to stay on glidepath. I guess my point here is that having an actual hardware throttle makes all the difference in flying a good approach in any conditions.

[Slayer 190]

Also the weight of the plane can have a huge impact. Wondering how much your cargo load was. Do you use TOPCAT or any other tool to figure out takeoff and landing perf? Maybe a lower flaps setting could help with the A/T having to modulate so quickly that it can't compensate.

[Chicken Patty 1]

I recently had a similar experience flying with the iFly 737 approach into KFLL.  Some bad weather, rain and winds.  On approach I did notice some sort of similar behavior to what you described and also as said above, some jockeying of the throttle by the auto throttle..  I ended up having to disengage it and fly it in manually which wasn't the best of landings but more stable than what the AT was doing for me.

[scandinavian13 5,192]

How you handle this is very, very simple:

Click, click

Click, click

"I have the airplane."

 

https://www.youtube.com/watch?v=R0rYX-Jn6o8

 

 

 

 

Within the limits of FSX, the autopilot has been developed to be as accurate as possible.  Even the real aircraft will have trouble in turbulence.

 

As always, there is more information about this in the introduction manual.  The reason that these manuals are written is to help explain all of this.  Please read it.  People made the effort to help you out pre-emptively.  You'd read it here, so why is it so tough to read it there?

[evaamo 549]

Also the weight of the plane can have a huge impact. Wondering how much your cargo load was. Do you use TOPCAT or any other tool to figure out takeoff and landing perf? Maybe a lower flaps setting could help with the A/T having to modulate so quickly that it can't compensate.

 

I do have TOPCAT using the latest beta which supports the 200LR/F. My landing weight was under 225 tonnes and TOPCAT suggested Flaps 30. Maybe landing at Flaps 25 might have helped indeed.

 

The reason that these manuals are written is to help explain all of this.  Please read it.  People made the effort to help you out pre-emptively.  You'd read it here, so why is it so tough to read it there?

 

I have read the introductory manuals, thank you. Twice as a matter of fact before even using SP1 for the first time. Had I not done so I wouldn't have asked in my initial post whether the turbulence filter option would have helped in my situation, don't you think?. My intention to start this discussion was to learn more about other's experiences in similar scenarios and to learn from more knowledgeable folks whether the real aircraft (or a Level-D) would have reacted in the same way. Thanks for the video btw.

 

Autopilot and Auto throttle have their limitations, your flight reminds me of my thundery approach into EGBB, the AP was connected and did its job just about. Which makes you think in RL would pilots continue the approach in WX like that or divert to alt?

 

In the particular scenario I depicted, I doubt any of my heavy iron flying buddies would have attempted to land there. The luxury of being in a simulator means we can try that without worrying about dropping out of the sky like a brick due to windshear or if the remaining FOB is sufficient to attempt another landing ;-)

 

BTW I later found out that the weather conditions were different in the "real world" at the time of my landing, but the depiction I got was due to the fact that ASN had stopped updating the weather conditions, which someone has just reported in another thread. That's why the time ActiveSky Next's ATIS was giving out didn't match the real Zulu time. I hope it's an isolated issue and not a bug in the otherwise very nice workflow PMDG designed for using the datalink to feed the FMC.

 

cheers

-E

[scandinavian13 5,192]

 

 

I have read the introductory manuals, thank you. Twice as a matter of fact before even using SP1 for the first time. Had I not done so I wouldn't have asked in my initial post whether the turbulence filter option would have helped in my situation, don't you think?. My intention to start this discussion was to learn more about other's experiences in similar scenarios and to learn from more knowledgeable folks whether the real aircraft (or a Level-D) would have reacted in the same way. Thanks for the video btw.

 

Welcome, and sorry - I was hammering away at the forums to at least get people pointed in the right direction.

 

I just wasn't understanding how it would still be a question after reading the intro manual.  The filter that's present in the plane helps, but you can see (by the graph in the same section) that the turbulence in FSX is far from realistic.  There are two ways to handle this: drop the turb in ASN (/weather program of choice), and/or adjust the A/T threshold in the PMDG Setup section (I'd do the former before the latter).

[evaamo 549]

Hi Kyle, don't worry, I understand. 

 

Thanks for your comment. It is indeed very interesting how FSX turbulence is unrealistically modeled and the approach PMDG made for trying to "normalize" the situation. In my case, using the keyboard to control throttle in all aircraft I use, it was the first time I encountered such a complex situation and ASN definitely makes thing more demanding for all add-on aircraft. In the NGX for example, I've hit some bad weather scenarios but manually controlling thrust using the keyboard was never an issue. With the 777 I'll be using my Joystick lever in the future. 

 

I also agree with you in your suggestions: reducing the turbulence in ASN is a more viable solution than experimenting with the 777X internals. Ryan "Tabs" in another post mentioned he lowered the "Maximum wind turbulence" setting from 100 to 50. I just did that and hope it makes things better.

 

cheers

-E

[Jamesie79 9]

Just arrived at WMKK. Terrible weather, scary landing. PMDG 777 + ASN = Awesomeness

 

 

[Don t moderate me this way 882]

Back in those ancient days pre SP1 we used to be 'children of the magenta line' ...

 

... now we are 'children of the magenta wx patches'!  

[whoispankaj 51]

Back in those ancient days pre SP1 we used to be 'children of the magenta line' ...haha..i love some humor here..

 

... now we are 'children of the magenta wx patches'!