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Robjaworski11

Bobbing up and down during VNAV DESCENT

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Hi everyone,

 

Whenever the PMDG 737ngx begins in descent in VNAV, throughout the entire descent the aircraft bobs up and down severely until it arrives at the altitude that is set in the MCP. I could understand if there was some light, moderate bobbing up and down during a descent, but this is severe and unnatural. Any help would be greatly appreciated.

 

Rob

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Are you entering the forecast winds for the descent? If I don't enter those I will sometimes get the bobbing up and down that you describe.

 

 

Sean Campbell

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Rob,

 

I haven't had that problem with the NGX but it was a serious problem with the 744X. Same flightplan, same weather (no weather at all really) and the NGX flew on rails while the 744 porpoised wildly until you got down to around 10,000 ft. To get around it I used LVLCHG from cruise down to FL100 and then re-engaged VNAV after that. It may be a weather problem with the NGX buit it certainly is not with the 744X.

 

Gerry

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Gerry - I have never seen this with the 400X. You can reproduce it in verified no/calm weather conditions?

 

Every instance of this sort of thing I've seen at support with the NGX has been weather related - the cloud "turbulence" is a major culprit because of how it unrealistically slaps the airplane around.

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Hi Ryan,

 

Yes, absolutely no weather set. No turbulence set and in the VNAV descent from FL370 I was getting 1700 fpm and then 2900 fpm nearly all the way down to FL100. As I approached that level the effects lessened so that below FL100 I could re-engage VNAV or simply VS with throttle to keep the green arc in the desired place. As I said it is not a problem with the NGX. It might need a touch of the speed brakes in descent occasionally but there is no violent "bobbing".

 

Gerry

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Sorry to post this as a replay but this issue is similar to mine..only oin the opposite direction. I get the same issue with the bobbing, however I get it on my CLB to CRZ Alt. Every flight I have done I have had to re-adjust my CRZ ALT to a lower one becuase I could never reach my planned ALT. I have tried Derated T/Os with no luck and I dont know where to get Descent winds from to input.

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Use optimum altitude from PERF INIT page and try to use default wheather FSX theme.

Derated take off thrust have no connection with climb perfomance, except initial climb to thrust reduction altitude.

I'm using descend winds given by active sky 2012.

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Hi guys,

I have this same bobbing effect going on aswell. As soon as the a/c gets about 150 - 200 feet airborne, it starts this rapid bobbing, and no matter what altitude i fly, it doesnt stop. its virtually unflyable. Very strange thing is, that it does it now with the stock fsx 737 too, but not with the pdmg 800 or 900 without the wingtips, only with wingtips. i have tried disconnecting and reconnecting controllers, but nothing works to fix it. I have a feeling its in a configuration somewhere in fsx thats stuffed up, but only affects 737's with wingtips, and no other aircraft.

 

cheers.

 

steve reddy.

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