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Clear-Air Turbulence in small aircraft...

This Sunday (22 March) we’re planning to fly from Lelystad to Morocco.
Looking at the wind forecasts for that day, it seems like we are really very lucky:

Huge tailwinds expected, which make it possible to get us far into Spain in one leg.
I’m planning to use Valladolid LEVD for refuelling. The route distance from Lelystad to Valladolid is 849NM, which with the expected tailwinds result in 4h56 flight time

The Gramet shows turbulence at altitude:

The forecasted winds at altitude are really strong, with forcasted tailwind of 84kts max.
Since my flights at altitude so far have always been smooth so far, I’m wondering what I can expect?
Should I plan the flight at a lower level in order to stay below (what seems to be) a jet stream?

Turbulence is forecast by algorithms such as this based on vertical shear – that is the rate of change of wind with altitude. You would normally expect to encounter some light, occasionally moderate bumps in those areas. However, the prediction of turbulence in cases such as this is not an exact science – you might find nothing at all with very high vertical shears, or some very unpleasant rough air with very little.

In a DA40 I would personally choose to remain below the forecast turbulence. You can always ask ATC if they have any turbulence reported at those levels and if it is reported smooth you have the option of climbing up and giving it a go, and descending if you don’t like it. You just have to bear in mind aircraft types reporting the ride as what is smooth to a bizjet may not be so to you!

London area

Is this the sort of horrid long-term turbulence which one often finds on airline flights?

Airliners, especially if flying easterly, like to sit in the jet stream (to save fuel) and then you get the chop the whole time – because the jet stream is a relatively narrow “tube” of fast moving air. Going JFK-LHR one can get 8 hours of being chucked around.

I have never seen that in GA and I have been up to FL200, sometimes for hours. That’s nowhere near the jet stream, normally.

Even when crossing the Alps or Pyrenees with ~40kt winds I never felt anything worth mentioning, flying say 5000ft-10000ft above the terrain.

84kt is something else though… but I still think it will not be a problem. Just make sure you cross the Pyrenees near Biarritz, where they are relatively low and also the wind on your wind map shows much less wind there. The wind depicted is not the jet stream – it is just normal airflow around high and low pressures.

Disclaimer: I passed the JAA IR Met exam purely by doing the computer test 35 times

Administrator
Shoreham EGKA, United Kingdom

I am frequently in the FL270-280 area with very strong winds (have had plenty of 100-140 knot winds recently) and there is rarely any turbulence unless it is mechanical (ie over the alps). I would go up and see how it is. If you get turbulence, slow down to manouvering speed or lower and descend.

I did have some turbulence in the Pyrenees recently at my cruise altitude but I have had strong winds there and had nothing before. Suck it and see.

Last Edited by JasonC at 20 Mar 16:30
EGTK Oxford

Don’t expect the wind to be exactly like that. Plan with less wind as plan B.
A forecast is not a precise science.

Last Edited by mdoerr at 20 Mar 22:36
EGBE - Coventry

I agree; if there is a tailwind forecast, I disregard it totally for planning purposes.

Also I would never play with this unless I had a fuel totaliser. 2014 was a year of epic headwinds, many of which were 2x stronger than forecast (e.g. 70kt instead of 35kt) resulting in some “5-6hr” flights taking about 8hrs.

Also most strong winds (say 40kt+) are the result of air being squeezed between a high and a low, and a small track change can produce a big wind change. And the forecast isn’t going to be that good in placing the highs and the lows…

Administrator
Shoreham EGKA, United Kingdom

Thanks for the feedback! I’ve picked Santander LEXJ for refueling. The first choice Valladolid with the terrain around it is not a good option with regard to icing level.
Santander is at sea level.

Tracking link: http://tracking.eurofpl.eu/6038PHPCAEHLE1503220810

Safe flying. If it’s clear, the approach into Santander is absolutely stunning!

London area

Quick update to give some feedback on the flight.
The actual wind at altitude was as forcasted. We have seen wind speeds up to 84kts at FL170:

The flight itself was very smooth. Occasionally we had some light turbulence; similar to what you encounter on an average VFR flight at 1500ft…
All in all a great experience! We did Lelystad – Santander in 4h22m and got groundspeeds of over 200kts.
The approach to Santander was nice indeed. This is on final RWY29:

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