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Aircraft Performance - Inversion Layer at 10,000'

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Aircraft Performance - Inversion Layer at 10,000'

Old 22nd Apr 2012, 17:19
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Aircraft Performance - Inversion Layer at 10,000'

How would you compensate in your aircraft for an inversion layer at 10,000 feet?

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Old 23rd Apr 2012, 04:53
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I'd probably fly inverted. Haha, geddit?
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Old 23rd Apr 2012, 05:22
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Freo, what do you think is going to cause an inversion layer at 10,000 feet?

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Old 23rd Apr 2012, 07:29
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Temperature inversion layers (hereafter inversion layers) frequently develop at a height of 4 km over the Indochina Peninsula in the month prior to the onset of the rainy season, but the inversion layers have not been systematically studied. These inversion layers are considerably higher than those of the trade inversions that typically occur over the tropical ocean at 2 km height
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Old 23rd Apr 2012, 09:05
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Unless your aircraft is so under powered/at performance limits when flying at 10,000ft, there should be little of significance to notice.

Of much greater concerns are the inversions found at take off when just airborne which will really focus your mind, especially if you lose an engine
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Old 23rd Apr 2012, 09:10
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Subsidence inversions at similar heights are common in the North West of Australia, and you would notice the performance degradation climbing through them. Once you notice the temperature increasing as you climb, it was usually worth winding back the speed thirty knots or so to zoom-climb through the layer.

You would also notice the dust held below the inversion, so the air was much cleaner and smother above them.
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Old 23rd Apr 2012, 14:44
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Thanks all for your contributions.

This was actually an airline interview question.

Any other ideas how to compensate for this, apart from adding more thrust if available or a zoom climb?
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Old 23rd Apr 2012, 16:56
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Are you sure the question related to 10,000ft and not 1,000ft?

It makes more sense to talk about the 1,000ft case, I think.

In one case (for the B747-400)

"TEMPERATURE INVERSION
If a significant temperature inversion is forecast or there is reasonable evidence of it's presence due to conditions (i.e. clear, calm, conditions at night) and the temperature is above ISA+15C, then 3C should be added to the reported tower temperature prior to calculating the TOPL weight and applicable Reduced Thrust."

On reaching the inversion level, by definition, the SAT increases and the without a thrust reduction the EGT will rise, possibly exceeding limits and requiring a (manual) thrust reduction. If you are seriously performance limited, this can result in the inability to accelerate and hence retract flaps and may even require a shallow descent to accelerate!

This effect is often noticeable in the Middle East at night as the surface temps drop after hot desert days or taking off from places like Entebbe over Lake Victoria where many people have experienced the phenomena.
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Old 23rd Apr 2012, 17:40
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10,000 ? I have seen 10 deg C sudden increase well above 30,000'.
So if you are in descent, no problem, if you are in climb & heavy your climb rate will slow down a lot....
 

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