thunderstorms

[lowbypass]

Flying perpendicular to a squall line, what is the closest 'safe' distance to fly near a CB cloud above say FL 310? (I was once told it is 40 nm and did not seem practical to me)...we fly close to CB's (when necessary) about 15 nm away, anybody?

[BOAC]

20nm is generally reckoned to be ok but is DOES depend on the activity level of the cell. In the Far East I would give it more!

[lowbypass]

Far East ones are more spicy I suppose!

[SNS3Guppy]

Your position from the cell makes a difference, as well as the conditions in which you're flying.

If you're downwind or downshear from the cell, you have more to concern yourself with than upwind or upshear.

As a ballpark rule of thumb, a distance of 1 mile or each knot of wind at altitude is appropriate. Above 25,000', avoiding all echoes by 20 nm is a good rule of thumb, though not always practical. Additionally, avoiding echoes you can't clear by at least 5,000, by a distance of 20 nm is good practice. Intense or extreme echoes should be avoided by at leats 20 nm, and if you're going to fly between them, you should have at least 40 nm distance (20 on each side).

When the temp at alitude is 0 deg C or higher, avoid all echoes by at least 5 miles. When the temp is less than 0 degrees, avoid echoes by 10 nm. Any weather with tops above 15,000 should be considered potentially hazardous; view it or penetrate it carefully. Weather above 20,000 should be considered hazardous. Avoid all echoes with radar tops above 30,000'. Note that this is radar tops, not cloud tops.

Fly at least a thousand feet above the tops for each 10 knots of wind at altitude, and a mile laterally for every knot of wind, when downwind of the cell. Look closely at the structure of the cell, too. A return which is green at your altitude and painting cell strutures behind (transparent and not attenuating) may be safe to transit, even though built up well into the flight levels...but you do need to use your tilt to examine the whole cell structure and see what's above and below.

Additionally, if the top of th cell is sheared, you may have very little in the way of returns, but may encounter significant turbulence near the cell, or for a fair distance downwind. The cell may be your only warning, as such conditions won't always be painting on radar.

The altitude of the cell is only part of the picture. The activity of the cell is another, and much more important consideration. A cell that only reaches though fifteen thousand can still pack a punch, whereas a glaciated cell reaching above FL350 may have nothing left and may pose little threat.

Any activity along a squall line should be considered significant until determined otherwise.

[Centaurus]

use (or used to when I did this stuff) the "dark and stormy night" test - could I do this myself in the aeroplane on a dark and stormy night having just flown 4 busy days, am totally shagged, and have an ineffective offsider

Depending on the type of radar (variable gain control or not), it is sound practice to scan ahead using the max manual gain position when above 30,000ft. Max gain will give you 3000% more power to pick up a top that may have very little moisture and will not show up at Auto gain. Some monsters in the Pacific will show up as a tiny blip on manual gain and nothing at all on auto gain. Once you spot this blip, then use tilt to evaluate further using variable gain.

[Pugilistic Animus]

for Ts avoidance: a good guide is---
avoid all echoes by---
Blo 25000ft:

abv freezing----5 miles
blo freezing--------10 miles

abv 25000 ft all temps ----20 miles



edited to say: all puddle jumpers, at all atltitudes--- 20 miles

[Pugilistic Animus]

SNS3 Guppy,

--- sorry was posting a thought I had earlier in the day w/o seeing your post had already beaten me to it with a much more in depth treatment of the subject---



PA