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Mango3
18th Jul 2001, 18:33
I crew a B734. Word has it that this type "bounces around like Dolly Partons most prominent feature". I do not refer here to her singing qualities. What's the ride like during a CAT encounter in a 777, A340 or similar heavy? I fly across the Tasman and get thumped periodically by CAT. Is it time to find a bigger aircraft or is the experience the same? Getting fed up spilling coffee and loosing the salt that the peanuts came with. Avoiding CAT is an art in itself. Haven't mastered this with the exception of watching TAT go ape, but by then it's too late. Any idea's?

Checkboard
18th Jul 2001, 22:43
You need to take a look at the Grid Wind forcasts for changes in wind speed with height first, The U.S.A.'s National Weather Service duidlines give 6 knots per 1,000 feet vertically and 40 knots per 150 nm horizontally as values of wind change indicitave of shear critical for Clear Air Turbulence (CAT).

These values are easily exceeded by the Jet Streams aorund the mid and southern latitudes in Australia. CAT around jetsteams is particularly bad where the jet is concave to the pole (i.e. in Australia on the southern edge of the jet, when it is turning to the south.) These are the places you will see the Met department predicting turbulence on the SIGMET chart. Undertanding where it is will allow you to make a diversion decision (i.e. North or South) to find smoother air, depending where you are in relation to the area.

Look also for subsidence inversions - typically indicated by that dirty brown line in the sky, sometimes you will see turbulence induced Altocumulous at this level as well. The air is smoother above the inversion, and quite bumpy around the inversion, due to the change in wind at that level.

Watch out for mountain waves on the Tassie ranges or the southern end of the Great Dividing Range when the conditions are right (wind close to 90° to the range, and increasing with height, stable day).

Most other turbulent areas are indicated by the presence of weather (i.e. fronts and the like.)

Brenoch
19th Jul 2001, 21:56
I would think the heavier the aircraft is the lesser it will be affected by CAT.
I fly both the 75 nī76 and the 76 is alot smoother allthough that might be cuz 75 harldy has any wings.. Flies on sheer power.. :)

HighSpeed
22nd Jul 2001, 08:34
hi mango,

i came off the b737 to the b777 about a year ago and i can tell you the b737 rides turb much better than the b777. i believe it's got more to do with the material the wings are build with. i recall the ride on the b744 was alot like the b737 probably better, maybe due to the wings flexibility? i have heard horror stories from a330/a340 guys regarding its ride thru turb. i think with the more composite material there is in the wings the less flexible it becomes...