Severe oscillations in cruise (P3Dv2.5)

[johnfairm 5]

Hi All,

I'm having a problem that is only occurring in the 777.

In the cruise phase I have very severe oscillations in the altitude. The plane will constantly drop about 1000feet then start climbing and then overshooting the set altitude by about 1000feet. The rate I'd decent/ascent can be as much as 6000fpm.

This occurs no matter what weather settings I use. It does it using ASN, standard sim weather and no weather at all. When using FSCaptain & ASN, FSCaptain will show heavy turbulence whilst ASN shows no turbulence at all. I've tried with FSCaptain off & the result is the same.

I have tested with other planes (Aerosoft Airbus A320/A321) and this does not happen, the cruise is fine.

My system is running on Windows 7 64bit.

Any assistance / advice would be appreciated.

Many thanks

John Fairman

[johnfairm 5]

Is anyone else experiencing this?

[CT5 1]

i am also a fellow 2.5 user with the 777 and i do not experience this, is there any chance your weather program could be a culprit, I use opus FSI, just a thought

[downscc 1,327]

i am also a fellow 2.5 user with the 777 and i do not experience this, is there any chance your weather program could be a culprit, I use opus FSI, just a thought

Full names in the PMDG forums please.

 

 

 

The plane will constantly drop about 1000feet then start climbing and then overshooting the set altitude by about 1000feet. The rate I'd decent/ascent can be as much as 6000fpm.

 

I've never experienced that behavior.  If it is doing this with no weather then I am at a total loss as to what is happening.  What are the indications on the FMA (PFD upper line in display)?  You should see an indication of what modes the AFCS is in such as SPD, LNAV and VNAV PATH or ALT for example.

[johnfairm 5]

CT5

I've tested without ASN and with no weather and it still does it.

 

Dan,

I was in a standard LNAV / VNAV cruise on autopilot. I tried turning the autopilot off but still couldn't get it under control.

Takeoff and landing, and even descent are totally controllable it's just in cruise that the problem appears.

I've been flying the 777 in FSX ever since it was released without any problem.

I think I may have to try a re-install and see if that cures it.

 

Thanks for your responses,

John

[Mike777 163]

Hi, John,

 

Which aircraft (200lr or 300ER), what is the gross weight, and what TAT is showing on the EICAS?

 

Mike

[johnfairm 5]

Hi Mike,

 

It happens with both 200 & 300. Probably won't be able to try another flight for a few days.

All flights were planned with PFPX and were well within weight limits. Can't recall what the TAT was. I'll make a note of it next time.

 

Regards

John

[Mike777 163]

Sometimes an addon program can inject a high air temp at altitude which will cause the engines to under perform. Might also reduce lift, not sure.

 

Mike

[downscc 1,327]

True, but generally the high SAT (best to check this instead of TAT) results in an inability to even get to a cruise altitude. It's still a good thing to check, rules out a bunch of problems.