I've been flying the PMDG 737-800 NGX from MDW to STL recently.  I've completed this flight several times without issue, but on my last two flights I experienced a strange "jump" (as in a rocket magically) from FL260 to FL310 and then on approach lost about 5,000 in a "falling like a stone" manner.  The only difference I am aware is that I have gone back to trying to use OpusFSX instead of AS2012 for weather.  While this correlates perfectly with the two flights I've had this issue, I can't provide a rational reason it should be an issue.  I looked through the local OpusFSX METARs and there were all about the same altimeter and temperature as before the jump/drop. 

 

The first flight I had FSX randomly minimize because I had accidentally selected the OpusFSX "Show METARs", so I washed it off due to this (it was about the same timing).  This last flight I actually pulled an FS Flight Keeper log to keep track of what was going on, but other than the change in altitude I see very little.  Before the jump to FL310 I did get a TCAS alert, however I have FSX collisions turned off, so I can't imagine what would happened there.

 

Anyone have any thoughts?

Opus.

Opus.

 

Am I to take this as meaning this is a known issue?  Or are you just saying so based on the circumstances.  I'm certainly suspecting as much, but I've learned when seeking support with OpusFSX, it's best to keep an open mind or be shutdown.

It has happened to me using Opus and the NGX at cruise, and using the new Twin Otter as well. But, over the last week it has seemed to stopped. Only difference is I continually update to the latest beta in Opus, and I stopped trying to use Opus over my network.

Eric. Funny you should mention this. I had the exact same anomaly while at FL310 cruise with the NGX. It suddenly jumped to FL330, then descended back to a very erratic FL310.

This was just today on a short flight from KPHX to KLAX.

 

I went into Opus Live Weather setup and hit set to defaults on the Weather Options, Weather Download Options, Smoothing and Stabilization and General User Preferences dialogs and everything settled back down to a steady cruise.

 

I can only assume that one of my custom settings caused the problem, so I guess the only way I can probably find the cause, is to reset my options one by one to see if I can replicate the problem.

 

Regards,

Opus.

Opus.

 

I guess I'll stick with AS2012.

Opus.

Jim,

 

Can you enlarge on this?

 

Regards,

Cause and Effect. One thing changed and one effect leads to the source of the change. No idea as to the reason for the effect.

The 'rule of thumb' is that for pressure changes of 1 inch Hg altitude diffference is 1000 ft.  Very useful if your altimiter is set incorrectly (or, maybe very useful in explaining why you flew your aircraft into the ground because you altimiter was set incorrectly).  The way to remember the effect is:

 

High to low, look out below (if your altimiter is set at a higher pressure than the actual pressure, your acutal altitude is less than the altimeter shows).

Low to high, you're in the sky - actual altitude is higher than the altimeter displays.

 

At higher altitudes the rule still holds based on sea level barometric pressure changes.  The pressure differece between FL260 and FL310 is about 2 inHg (or ~ 0.4 inHg per 1000 ft).  But to get that much change in pressure to cause an aircraft to jump from FL260 to FL310 the barometric pressure would have to change ~ 5 inHg at sea level - not something that happens.  And, at or above FL180 aircraft fly at pressure altitude - the altimeter is set to 29.92 inHg.  So if the actual sea level pressure is changes your altimeter will not change but the actual altitude will - but an change of 1 inHg sea level pressure would still result in about a 1000 ft difference in altitude at FL260 because the proportional change in barometric pressure at that altitude would be about 0.4 inHg.

 

Maybe this explains Rick's 2000 ft change.  Maybe not.  But regardless of all the physics -

 

Opus.

 

(Right Jim?  :rolleyes: )

Just update to the latest Beta, we experimented in a recent trial adjusting the altitude based on the turbulent airflow and motions, this has now been removed. I am not sure if it found its way into the release version but if you upgrade to the latest beta it will be fine.

 

If anyone is going to use the Beta versions then please sign on to SimForums and follow the latest Announcements and progress there.

 

Cheryl