Crossing the ITCZ

[Ozgrade3]

A question for the jet guys.

When crossing the Inter tropical Convergance Zone, in a Jet, is higher always better. If you aircraft can get to FL 450 does that put you clear of most of the nasty stuff?

In this sort of area, where one can expect deviations and possibly turbulence, is it wiser to stay visual or will wx radar give you a good enough picture to pick your way round the cells.

Also, if you chose to go high, if that puts you right on the altitude limit for your weight, is that dangerous or should you be lower towards the optimum altitude for your weight.

Any difference in the strategy you would use in a light jet (Citation) compared to a 767/747 category aircraft...ie heavy.

Lastly as an aside issue, whats the highest CB anyone has seen. I jumpseated on a 76 one time and we were at 390 or 410, we went round one cell and I had to look way up to see the tops. Was most impressive.

[Cypher]

When crossing the Inter tropical Convergance Zone, in a Jet, is higher always better. If you aircraft can get to FL 450 does that put you clear of most of the nasty stuff?

Higher ain't always better, it relates more to what you said later on

Also, if you chose to go high, if that puts you right on the altitude limit for your weight, is that dangerous or should you be lower towards the optimum altitude for your weight.

If you head towards the top of your max height /optimum altitude, yes, you are running into 'coffin corner', go too fast and you hit Max Mmo, too slow and you stall.... so most of the captains I fly with tend to go no higher than 1000 ft above optimum altitude. If we're expecting turbulence, I personally would rather be lower down with a good buffet margin. The turbulence tends to make the airspeed dance around quite a bit.

In this sort of area, where one can expect deviations and possibly turbulence, is it wiser to stay visual or will wx radar give you a good enough picture to pick your way round the cells.

Most captains I've flown with, prefer to stay visual. And it makes good sense, why fly through crap if you don't have to. The only time most of them would use the radar to pick their way through it would be when there is just a line of storms and there is no other way around them. Then its a case of avoiding the areas of the strongest returns and looking for 'shadow' spots that could be hiding even nastier turbulence.

Any difference in the strategy you would use in a light jet (Citation) compared to a 767/747 category aircraft...ie heavy

In a light jet you can generally get to a higher altitude earlier. And take the higher levels before most of the airliners can take em..
I found that the lighter jets tend to have their 'coffin corners' at a much higher altitude, allowing you to stay at the higher levels to ride out the bumps.

Lastly as an aside issue, whats the highest CB anyone has seen. I jumpseated on a 76 one time and we were at 390 or 410, we went round one cell and I had to look way up to see the tops. Was most impressive.

Hmm, well if my maths was correct, using the radar, I think we worked it out to be around FL510....

[18-Wheeler]

Lastly as an aside issue, whats the highest CB anyone has seen.

I went past one near Townsville in the 1990's at 41,000' and we were no more than about 2/3's the way up it. Had to be up near 60,000'.

[empacher48]

We cross the ITCZ and SPCZ about two to three times a week in a medium turboprop at about FL 200 (of course depending on where they are, at the moment they're still further North). The weather radar does help dodge most of the worst parts. The icing at that level is phenomenal. So having the ability to change height (usually down) to get out of it is good.

[zlin77]

Highest CB, BNE Dec.'89, ground based Bureau of Meterology radar reporting tops of 72,000 Ft. it's baby brother about 20 miles away was only 55,000Ft.

[Dog One]

Just the right size to pop into in the C150 to get a bit of altitude!

[tinpis]

Crossing the ITCZ
A loud klaxon sounds on the flight deck
Everyone stands to attention and sings "Advance Australia Fair"

What do you think happens?

[illusion]

Ozgrade3,

The cells are usually spaced enough to get around them without too much trouble

1. Divert early rather than when you are on top of them.

2. There are often narrow, tubular cells that don't paint at all well on the radar and can give a nasty wake up if you are unlucky enough to fly into one

3. Winds are usually light, however usually best practice to divert upwind
to avaid anvil etc


4. ISA deviation can change quite significantly in a short time/distance as you near a cell eg from ISA + 5 to ISA + 17. This can cause grief if you are at/near the max altitude for the aircraft as you are suddenly 1000' or so above it!

Safe Flying