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Nakkis

Weird behaviour while on final approach

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Hi,

I've been having weird problems at landings for some time now. These events are pretty random and can take place at any airport. Last time i had it at Santorini and this time at LEPA. I've also experienced the phenomenon at Fuertenventura.

Everything goes well until i reach about 300 to 600ft when suddenly airplane shakes (like slowing down at first, then accelerating instantly) a little, starts levelling off and even climbing even though yoke is fully pushed forward. I did some testing, and i could repeat it at LEPA rw 06L. It has happened twice with AS Mallorca and AS2012 weather in different conditions but with FSX fair weather and default airport also, everytime at same height and distance from rwy. I have disabled all up/downdrafts and thermals in AS2012 and have no smoothings at FSUIPC. There are no wind/pressure/temperature shifts when this occurs. 

I attached some photos from a testing approach to 06L at Palma with NGX and FSX Fair weather.

All i know is that it ruins my landings and it's pretty annoying. Once it strikes while landing, it will be at the same spot even after go around so only help would be runway change or diverting. 
I have no idea what's causing that but if anyone else has experienced same thing and has gotten rid of it I'd like to hear how.

- Osku
 

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Nope, no buttons pressed. There would be TO/GA indications on the FMA and go-around thrust set to in that case.

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@James Bennett  I don't see on the panel where the TO/GA was activated so doubt the OP accidentally hit that.  That would do it though if it was activated.

 

@Nakkis  How did you come up with an airspeed of 145?  I do not see any speed bugs set.  This has happened to me on a couple of occasions when my speed goes below what is required to keep the aircraft in the air.  I start to get a stall and the aircraft shakes.  It's hard to read the Approach Ref page on your FMC but you do know you should set your speed bug.  There are different speeds for different flap settings.  On the FMC I hit the LSK for flaps speed at 40 and enter it in the area below that.

 

Best regards,

Jim

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Hi Jim.

Are you talking about those bugs which say 5, 15, etc? They disappear once you're in final approach in landing configuration and re-appear if you perform a go-around and start retracting the flaps.

You can see the green Vref bug/mark at 140knots on the PFD. It's there as i've set the approach ref on the FMC to 30/140 according to the weight. VAPP is set on the MCP as the speed mode is activated and autothrottle is keeping the right speed. The FMC might not be fully configured as that was only a test flight.

I don't want to sound rude, but i'd like to point out that I have almost 2000hours of experience at IVAO and over 300 on the NGX so i (atleast) think i'm flying the plane in a way that the problem is not caused by "pilot error". :)

- Osku
Few photos to point out the bug thingy:


: index.php?action=dlattach;topic=106335.0
During go-around:
index.php?action=dlattach;topic=106335.0


EDIT: I'll try to upload a video tomorrow to clear things more. I'm not native english speaker so i might not be able to describe that problem enough.

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It's there as i've set the approach ref on the FMC to 30/140 according to the weight.

 

But I did not see the Vref in the pictures in the OP.  I usually see the Vref at the bottom of the speed bug such as "Ref 140/40".  I do see you have the reference showing up at about 145.  I still think you are encountering a stall for some reason.

 

Best regards,

Jim

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That's because i fly with Transavia and it's their customer option not to show landing flaps on the PFD. (Settings/Displays/ page 3/9). If it was on you'd see them there  :wink: 

As i said before, the approach ref page is set correctly (well, i lied a little there as i burned some fuel after setting those speeds and the correct Vref was 139 at the time) according the landing weight. Vref is at 140, Vapp is on the MCP and set to 145 as there were no winds.

I added a larger version from one of the photos where the approach ref is visible. I double checked those numbers with topcat (winds 000/00, temp +17, QNH1013, a 737-800 with flaps 30 and GW of 57800kg and it also says Vref 139, Vapp 144)

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It's not a big hassle to reinstall it, I would try that.

 

Sounds more like a glitch than a user error.

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the approach ref page is set correctly (well, i lied a little there as i burned some fuel after setting those speeds and the correct Vref was 139 at the time) according the landing weight.

 

It definitely sounds like you had the FMC and your approach setup completed properly.  I always set my approach speed a little higher than the Vref.  So your setting of 145 should not have been a problem.  Next time I would try turning off the A/T Arm when you get to that level and manually operate the throttle until landing.  Again, it sounds like your aircraft is stalling (but it shouldn't as all of your approach settings appear to be proper).  I agree with Iain above, it appears to be more of a glitch than a user error.  Gee, I was hoping to get this one solved right away!

 

Best regards,

Jim

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thanks for the tips so far for all of you.

To me it looks like some kind of turbulence/shear eventhough there are no changes in the numbers. I'm currently trying to upload video about what happens on final. It's kinda difficult to explain. I've tried landing without autopilot & throttle but it does'nt seem to help. + I don't fancy reinstalling sim as i did it only few months ago when i had to re-install windows.


Edit:

Well, here it is. Not so great quality as i filmed it with my phone but i think it poins out the problem:
When "it" hits, the angle of attack indicator goes crazy from the steady 4-5 jumping between 8 and 2 degrees



- Osku

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Nice landing.  I did not see anything out of the normal.  Even though you have no weather or just fair weather running, there still is a periodic gust to give some realism and that looked like you got into some kind of air pocket.  Maybe someone else sees the issue.  I don't.

 

Best regards,

Jim

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Very clear to see! Some crazy updraft or false weather effect or a bug. I fly in all kinds of bad weather but I've never had that happen.

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how does it fly a manual approach?..the ils is just dropping out, and its trying to chase it.

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That happenes me in the Quality Wings 146. It feels like the back of the aircraft is being pulled up.I had always put it down to pilot error on my part because i didn't read the manual.Maybe its a bug after all.

 

Never had it happen flying the NGX.Hope you find an answer.

 

Oh and good job setting her down.Nice Work

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This looks like what I always encounter on a northerly approach to KPAE when using the default Fair Weather theme, and even then when I start up Active Sky I still sometimes get this updraft. Before loading the flight, and after starting Active Sky, try switching from User Defined to Clear in FSX or else flushing it out using FSUIPC before starting AS. Either of these things should get rid of it.

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Maybe it's just random FSX thermals, you could try renaming ThermalDescriptions.xml to ThermalDescriptions.xml.sav and restart FSX. Look in "C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X" or wherever you installed FSX.

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I think Steve is onto it. Sounds like that thermal xml to me too. Also in AS2012, make sure wake turbulence is turned off.

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Maybe it's just random FSX thermals, you could try renaming ThermalDescriptions.xml to ThermalDescriptions.xml.sav and restart FSX. Look in "C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X" or wherever you installed FSX.

 

I'm sure that's it and was about to post the same answer.

 

Unfortunately when having the ThermalDescriptions.xml not turned off, it places some thermals right in front of some runways and causes the anomaly seen here. It's happened to me at a few airports off the top of my head are KPHX when approaching runway 26. KDAL when approaching 13L or 13R and one of the runways at LSGG (can't remember which one).

 

Simply renaming the file to ThermalDescriptions.xml.off fixed the problem for me and now dont have to worry about any thermals right in front of runways any longer and by renaming that file allows me to still have turbulence turned on. Otherwise if you uncheck the that box in the FSX menu, you lose both thermals and turbulence effects. Now I just let AS2012 take care of the thermals which aren't preprogrammed into specific areas of FSX.

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Be sure to edit the strength of thermals in the AS2012/WX Options/Wind Options panel, bottom right side. I have those lowered to 200/200 and it helps. Also be sure Wake Turbulence Strength is set to 0. It can cause havok with certain addon aircraft.

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Wow, thanks everyone and especially Steve!

Renamed ThermalDescription.xml and just made a test approach to Mallorca having no problems at all. Smooth all the way down!
 

- Osku

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In your video the N1 mode is G/A that could be a problem too.. Looks like you fixed it, but check your modes :)

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