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Altitude And Turbulence  
User currently offlineJoakims From Sweden, joined Jan 2002, 55 posts, RR: 0
Posted (4 years 10 months 4 weeks 11 hours ago) and read 7617 times:

Hello

I have a question about altitude and turbulence.
Is a higher altitude always equal to less turbulence?

Or is it only due to less fuel burn what mostly airplane seeks higher altitudes?

During my trips to Asia and special bay of Bengal it is almost always turbulence even at higher altitudes. But then starting to descend then getting nearer to destination and getting to lower altitudes and below layer of clouds the weather is almost always calm.
Even if it was turbulent above or near those clouds.

I think the pilot is the most skilled to choose what to do. This somethings i have noted during my trips. Is there some thing like descending to get out of turbulence.

Joakim

2 replies: All unread, jump to last
 
User currently offlineRFields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 1, posted (4 years 10 months 4 weeks 8 hours ago) and read 7466 times:

There is no 100% answer to your question.

Turbulence related to visible weather systems storms does tend to be less at higher altitude. But storms can reach higher than any civilian aircraft can fly.

CAT - Clear Air Turbulence - on the other hand is much less predictable and much harder to avoid if it is on your route.

Certain areas of the world are very prone to weather disturbances - the ITCZ - Intertropical Convergance Zone - tend to have rough weather much of the year. But like most other regions, this can be seasonal.

The Bay of Bengal gets a share of ITCZ weather during part of the year.

While flying at high altitudes is what aircraft are designed to do and to have the best fuel economy, pilots will descend if (1) they know the turbulence exists, and (2) they have other pilot reports that there is actually better weather lower.

But if the clearest weather is very low - 15,000 feet or even lower - jets cannot fly their complete routes at those altitudes. The fuel burn is too high and would force unscheduled intermediate landings.


User currently offlineG4LASRamper From United States of America, joined Dec 2006, 170 posts, RR: 0
Reply 2, posted (4 years 10 months 4 weeks 7 hours ago) and read 7421 times:



Quoting Joakims (Thread starter):

Is a higher altitude always equal to less turbulence?

Depends on what is causing the TB. But generally, yes higher altitudes usually have more stable air, so the ride up there is usually smoother.

Close to the ground one can experience mechanical and/or thermal TB, caused by things like the wind as it flows around or over objects (mechanical), or by daytime heating of the ground (thermal). Where I live we get lots of these kinds of TB. To avoid this kind of TB, higher altitude is better.

Quote:
Or is it only due to less fuel burn what mostly airplane seeks higher altitudes?

Is there some thing like descending to get out of turbulence?

I think you're correct - fuel burn is probably the biggest factor in selecting a cruise altitude. So, if only looking at fuel burn, higher is better. But if the planned course of flight happens to coincide with a jet stream, another altitude (higher or lower) may be needed in order to get a smooth or at least smoother ride. This is a case where lower altitude might give a better ride.

If the planned course of flight will pass downwind of high mountain ranges and a strong wind is blowing across the ridges, all flyable altitudes downwind of those ridges may be quite bumpy in that area that day. The stronger the wind, and the more stable the air, the wider the area of this "lee wave" effect. Again, where I live (the lee side of the Sierra Nevadas) we see this condition quite often. If the aircraft can fly above the waves, the ride may be pretty smooth. Below the tops of the waves can be quite rough since the aircraft will not only be dealing with the waves, but probably wave rotors as well. Here, higher is better.

Also, wind speed generally increases with altitude. If the planned course of flight runs downwind, higher altitudes may be better. If the course is into the wind, a lower altitude may be better, depending on the fuel burn at that altitude and the amount of time one will spend there. So this is another thing to consider when choosing a cruise altitude.

Quote:
I think the pilot is the most skilled to choose what to do. This somethings i have noted during my trips.

Of course, before a Part 121 flight is released, both the aircraft commander and the dispatcher work to choose best altitudes to fly. Once in flight, if conditions are not as expected, the pilots will consult with dispatch to see if there any better possible altitudes or routes, but in the end the final decision rests with the aircraft commander.

Tailwinds,

Paul



"A pig that doesn't fly is just a pig." - Porco Rosso
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