View Full Version : Jetstream

26th Oct 2008, 23:41
Flew Northbound yesterday and crossed a Jetstream at 90 degrees that had a core speed of 220kts. That's a personal record. Watching the HDG change was unreal as we went through and out the other side.
It was pretty smooth too. Not what we expected. The FO said she had a 190 kt tailwind earlier in the week heading Eastbound.


27th Oct 2008, 00:39
I guess the force was strong in that one :ouch:

27th Oct 2008, 00:40
Tom, just for my personal info, do you encounter any sudden turbulence as you penetrate a jetstream at an angle, or is the wind change gradual?

28th Oct 2008, 18:17

From a purely physical point of view, I should imagine it would be a pretty smooth ride, albeit noticeable. My reasoning behind this is to think of an aerofoil moving through the air - consider the surface of the aerofoil and the boundary layer of air to be the jetstream core. Now think how this affects air for some distance away from the aerofoil itself, right up until a point of sufficient distance from the aerofoil that it is no longer affected. So it would seem the logical answer to me is that it would be a gradual change.

Of course I stand to be corrected :ok:


28th Oct 2008, 18:38
Shows how little you know! Lad, you dinna know what yer talkin' aboot! Try piloting in a jetstream before you tell us the theory!

28th Oct 2008, 23:02
Once asked to hold at F/L 200 at a VOR/DME fix ( wot's FMS ? ) approaching Tokyo from the South, wind in the region of 180 kts abeam, turned outbound and was swept far, far, away. Eventually held at right angles to the required airway, 10 secs outbound, 5 minutes inbound - or something - interesting anyway.

Before anyone tells me that you don't get jet streams at that altitude - it was still a bl**dy strong blow, and remember what downed the 707 on Fuji - winds of 200 kts recorded around the mountain that day.

Hot 'n' High
28th Oct 2008, 23:18
HBB, next time watch what happens when you land and the wind drops and backs (assuming you are in the Northern Hemisphere) from 30kts to, say, 15kts in about 1500 ft! The aircraft will be all over the place in the windshear!!! Now, try that at FL350 with a 220 kt wind with appropriate windshear thrown in! Mmmmm, the coffee goes everywhere! Not much fun! If you suddenly fly into an updraught of +50 kts the Boundary Layer has nothing to do with it - you are in a "lift" plain and simple! You are going up - or down - at huge speeds! By the way, check out the texts on CB's! Avoid them as well if I were you! Alas, "windshear" and updraughts/downdraughs in CBs can cause significant damage! So, please, stay safe! And learn from others!

Cheers, H 'n' H!

PS Not patronising you in any way - just be aware that any change in windspeed, for whatever reason, can spoil your day.

29th Oct 2008, 16:11
H 'n' H,

Thanks for the clarification. No, my only reasoning was thinking that a jet core travelling at 200 kts will then affect the air in near proximity to it, and so on and so forth. 'My' theory was that if this process happens over, for example, 30 nms or so (laterally speaking) then although the change would be noticeable, it would cause no caffeine spillages as you said! But as I suspected, I do stand corrected!

Mind you, I'm sure that, like universal black holes, jetstreams come in all shapes and sizes, some 'shallower' than others so to speak. After all, as wxjedi mentioned, it was a smooth ride for him :ok:

Rainboe, thank you for your enlightening contribution also :D

Cheers, Jack

Hot 'n' High
29th Oct 2008, 21:55
HBB, no problems. As you note, sometimes there is a very smooth gradient and the coffee remains where intended! Other times .!!!! Often, there is no logic behind the outcome. I have always adopted the approach where I expect the worst. After all, one can only be pleasantly surprised by a potential bad event not taking place! Far better than being caught unawares. With Jetstreams in particular, there is no reason to assume a constant change in velocity as you approach the core. Why? If you ever find out, please do let me know!!!! LOL!

Cheers, H n H

31st Oct 2008, 22:21
did anyone ever try to cross a "dual jetstreams" at an angle at aprox 90 deg ??

What i mean is 2 jetstreams that follow the same way, as seen on the sign.chart.

I did, and tell u what, we had to wear shoulder harnesses just to fell safe. **** it was turbulent.
Anyone has a good explanation on why it is so violent with 2 jetstreams?
My cpt, gave me an explanation, that i didnt really understood at that time.