Hello all,

Some thing new for me, I'm currently cruising at an altitude the aircraft is saying is FL370 (STD (1013Hpa)). The actual aircraft altitude is FL320! I do not know how the aircraft can be so far out :S

 

Please find an image below with the actual alt show in red at the top left. 

 

 

Fixed! No problems with the aircraft. It was the weather Engine (Opus)

Fixed! No problems with the aircraft. It was the weather Engine (Opus)

If you care to elaborate on this, what made you believe the NGX was 32000 feet? And how does Opus fit into this situation?

 

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If you care to elaborate on this, what made you believe the NGX was 32000 feet? And how does Opus fit into this situation?

 

if  you would  have  noticed  on his  screen top it  says  32000   feet  where as on the ngx  it  says 37000  must have  been opus  since  he  says  its fixed

Your eyes are better than mine. I still don't see even after you told me where the 32000 feet is located.

Your eyes are better than mine. I still don't see even after you told me where the 32000 feet is located.

On the very top of his pic in red 32063 to be precise,  sorry my mistake it wasn't 32000

The only time those two numbers will agree is when there are standard atmospheric barometric conditions. Sound like a misunderstanding of pressure altitude.

Old topic, but for the difference of almost 5000 ft, the pressure argument probably isn't the most accurate one. That's almost 5" of pressure difference between standard and actual pressure at that altitude. That's very unlikely (impossible?) in the actual atmosphere at that altitude.

 

 

That's almost 5" of pressure difference between standard and actual pressure at that altitude.

 

Below 10,000 ft yes, but density lapse rate is very non-linear as you go higher.  For example, half the atmosphere by weight lies below 14,000.

That's a good point, but instinctively, 5000' difference still strikes me as significant. In any case, all this is a purely academic musing, as the original problem was fixed :-)

Yeah, academic but it is a slow Saturday and this is the closest I can get to hanger talk:  I found a std atmosphere calculator and found pressures at 30000 and 35000 ft vary by 62 mb., less than 2-inHg.  So it's a very measurable difference but not unrealistic, especially on a warm day.

Slow Saturday, indeed! Yeah, that is plausible, and as you said non-linear. Still, that's very close to the expected 1" for 1000ft. However, 32k-35k difference of almost 5" is dramatic.

 

The temperature at that altitude is not a factor, as you are likely already in the stratosphere where there is no temperature lapse rate as on the lower altitudes.

 

 

Still, that's very close to the expected 1" for 1000ft. However, 32k-35k difference of almost 5" is dramatic.

 

You missed my point, sorry, the change over 5000 ft up there is less than 2-in not 5.  The temperatures up there have been about 10C above standard all summer here in the US... the top of the troposphere is a little higher when you reach about -60C so we're not quite in the stratosphere yet.  Interesting stuff this atmosphere.

Yeah sorry, I misspoke, I wrote stratosphere, but meant troposphere. Now, my 5" comment comes back from OP: 32000 vs. 37000, which is 5000ft, or close to 5" pressure difference.

 

 

Now, my 5" comment comes back from OP: 32000 vs. 37000, which is 5000ft, or close to 5" pressure difference.

 

Nope, sorry not 5 inHg but only 1.71 inHg.  Handy calculator here: http://www.digitaldutch.com/atmoscalc/