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I am just curious about this... during one flight on Airbus A321 we experienced turbulence and the pilot told us that the wind speed is 150 km/h, so we won't get drinks and snacks due to safety reasons. The question is: Was that wind speed 'normal' or 'dangerous'? What could happen?

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    $\begingroup$ I can assure you there's nothing dangerous about a high wind speed on its own, the 'wind' the aircraft is facing is always the same as it moves relative to the air. Kind of like a boat on a river, if it's going up or downstream, it'll move slower or faster relative to the shore, but it'll be moving with the same speed across the water surface. As for whether it's normal (I think jetstream wind speeds can actually go higher than that), I'll leave that to the meteorologists among us. :) $\endgroup$ – falstro Mar 9 '14 at 12:08
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    $\begingroup$ FWIW, 150 km/h isn't that much wind at altitude. I'm used to thinking of wind in knots. 150 km/h is approximately 80 knots, and when crossing the North Atlantic in MNPS airspace during the winter, which was arranged to take advantage of the winds eastbound, wind speeds in excess of 100 knots were common. $\endgroup$ – Terry Mar 9 '14 at 22:38
  • $\begingroup$ @Terry true, but you won't find many A321s crossing the north atlantic, let alone loaded with passengers, and even fewer in winter :) $\endgroup$ – jwenting Mar 18 '14 at 7:55
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    $\begingroup$ @jwenting Actually, A321s do cross the Atlantic in regularly scheduled passenger service via Iceland nowadays. See WOW Air. $\endgroup$ – reirab Jul 21 '15 at 15:55
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    $\begingroup$ @jwenting British Airways even flies their A318s across the Atlantic from London City Airport to JFK via Shannon, Ireland and direct from JFK to London City. $\endgroup$ – SMS von der Tann Nov 22 '15 at 0:20
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High windspeeds themselves are not a problem, but the environment surrounding them may be.

For example, in the wintertime it is not uncommon to find a strong core of fast winds embedded within the polar jetstream. We term this windspeed maximum a 'jet streak'. There are a couple of meteorological phenomena associated around these jetstreaks, such as regions of ascent and descent in the entrance and exit regions of the jetstreak and often times turbulence in the periphery. You'll also find regions of turbulence on the lateral extent of the jetstream (polar side in particular). Lastly, if you are flying at an angle to the jetstream or perpendicular to it, you will often experience changing wind direction along with speed, and this can be turbulent.

There is nothing dangerous about that wind speed alone. What likely happened is that other airplanes were reporting turbulence and the pilots were being cautious with you and just offered that wind speed up as an easily understood number to justify the precaution.

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It's not unusual for aircraft to experience a lot of wind at altitude. In fact, there's a website dedicated to speed records- all of those shown would be impossible without the help of the wind boosting the aircraft in addition to its normal speed. Many people have unknowingly travelled at a velocity faster than the speed of sound on the ground when crossing the Atlantic.

While I'm not too familiar with it, I think that jetstreams and the like have a tendency to develop more air pockets and turbulence than calm air, including clear air turbulence, where there are no visual cues before the turbulence hits.

Many incidents happen when people are unprepared for a bounce at cruise altitude, probably hence the pilots decision. A broken ankle is not unheard of. As for catastrophic consequences, they are very rare. Typically, the pilot will slow the aircraft down a little to reduce shaking and stress on the airframe.

Here's an incident on a Cathay Pacific 747 around a month ago, midflight:

enter image description here

Passengers reported the turbulence appeared to have lasted for about 2 minutes, at the time the fasten seat belt signs were not illuminated, passengers and cabin crew were moving through the cabin, when the aircraft suddenly and unexpectedly jolted throwing passengers and cabin crew to the ceiling causing damage to ceiling panels and overhead lockers. Aviation Herald

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  • $\begingroup$ Well, not supersonic :) but a ground speed higher than the speed of sound $\endgroup$ – falstro Mar 9 '14 at 13:26
  • $\begingroup$ Haha, yeah, I remember flying on a BA 767 from KSFO to EGLL with a G/S of 1030 km/hr with a 160 kmp/h tailwind! But there wasn't any indication of turbulence and the seatbelt signs stayed off. $\endgroup$ – shortstheory Mar 9 '14 at 14:59
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    $\begingroup$ The reduction of speed is not to reduce the shaking and won't have much effect on it. It is to avoid exceeding the maximum permitted speed (Vne) in gusts of head wind. $\endgroup$ – Jan Hudec Mar 9 '14 at 21:53
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    $\begingroup$ That Cathay Pacific incident is an excellent reminder of why you should keep your butt in your seat with your belt fastened during the flight unless you've got a good reason to be up and moving around, regardless of what the signs say... $\endgroup$ – voretaq7 Mar 10 '14 at 22:05
  • $\begingroup$ "pockets of turbulence" is a misnomer. turbulence is caused by wind shear (or gradient), which is defined as the difference in wind speed and direction over a relatively short distance in the atmosphere. $\endgroup$ – rbp Apr 9 '15 at 13:12
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To put wind speed in perspective (further to the previous remark that 150 km/h is not fast at altitude): The speed of the Jet Stream is typically 100 kts (185.2 km/h) but can reach 200 kts (370.4 km/h) over North America and Europe in the winter. Speeds of 300 kts (555.6 km/h) are not unheard of, particularly over south-east Asia. Aircraft flying west-east will try to exploit the Jet Stream to increase ground speed and, similarly, aircraft flying East-West will plan to avoid the Jet Stream.

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