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Acceptable turbulence

What would you consider acceptable turbulence?

On my last few flights I ran into a few situations that allowed me to discover some clouds from the inside. I still find it hard to tell whether a cloud has already lost most of its energy or will be quite violent on the inside.

Obviously it is quite easy to recognize a CB and a TCU but “regular” Cu apparently can be quite wet (icing) and punch you hard.

Yesterday I was flying from EDTH (Heubach) to LELL (Sabadell) and Achim and I were on the same frequencies for most of the trip. Achim, you may have seen the Cu over the Pyrenean near PUMAL. I had to go through that area. The first one I went through at FL130 but then quickly decided to flee to FL160 to get over the stuff. There was no ice but – to me – strong turbulence.

So I’m wondering what is the scale for turbulence. When is it beyond what can be considered “normal”.

Frequent travels around Europe

You have a turbo and O2. So I would never have gone into that cloud at FL130 if FL160 tops it. Not even just to “see how bad it is”. Any unnecessary turbulence is too much.

Frankfurt (EDFZ, EDFE), Germany

Yes. Same conclusion. Lesson learned.

I guess there was this “you are flying IFR and should maintain your flight level” thinking.

I’m getting more assertive with ATC step by step too.

Frequent travels around Europe

Yes, but even better is to “move” early, not at the last moment and then present ATC with an urgenc situation.

Flying IFR does in no way mean being somehow constrained to a certain level or route. You can change it 100 times if needed. Just need to ask (if in controlled airspace).

Last Edited by boscomantico at 19 Sep 13:53
Frankfurt (EDFZ, EDFE), Germany

The ICAO definitions are below

Light turbulence is the least severe, with slight, erratic changes in attitude and/or altitude.
Moderate turbulence is similar to light turbulence, but of greater intensity – variations in speed as well as altitude and attitude may occur but the aircraft remains in control all the time.
Severe turbulence is characterised by large, abrupt changes in attitude and altitude with large variations in airspeed. There may be brief periods where effective control of the aircraft is impossible. Loose objects may move around the cabin and damage to aircraft structures may occur.
Extreme turbulence is capable of causing structural damage and resulting directly in prolonged, possibly terminal, loss of control of the aircraft.

It’s important to remember the mass of the aircraft (inertia) and wing loading also have a massive effect on how a given level of airmass disturbance is experienced. Visual evaluation, together with knowledge of the area is important.

Orographic lift over hills and mountains can produce seriously nasty effects in clear air – I would strongly recommend not flying through any form of convective cloud over the Alps or Pyrenees.

Last Edited by Josh at 19 Sep 15:28
London area

When I first had the SR22 i flew through some convectice clouds in FL120 at -3 degrees on a straight line. But after I had some interesting encounters with ice and turulence I quickly gave up that method … and over the mountains i would never do it anyway, I find it too scary and unpredictable.

Last Edited by at 19 Sep 16:00

Flying through this (or really any “white fluffy stuff” in the summer) is likely to be bumpy and uncomfortable

Flying through one of these (CU) is likely to be very rough, and a GA autopilot may disconnect due to excessive momentary pitch/roll angle

Flying through one of these (TCUs) is likely to render the aircraft uncontrollable, and may break it if you are anywhere near Va

Flying through this (a CB although a rather tired one; I can find better ones with more time) is pretty dangerous. You can get away with it and many have (generally by slowing right down and gritting their teeth) and many have not. As far as is known, the only airborne breakup of a TB20 was in a CB in Sweden.

Here is a bigger CB

Flying through any IMC between 0C and about -15C is very likely to produce airframe icing, and may ice up the air intake system on the engine even if it doesn’t ice up the airframe.

So the name of the game is to fly VMC to the maximum extent possible. The phrase to use is “request XX degrees left/right to avoid”. ATC will not refuse a request with “to avoid” and if they did or (this is not uncommon, especially if they are busy) they don’t reply, just do it anyway. They can see you on radar and they can take care of other traffic, which anyway will be 99% very high perf stuff (big jets; there is almost no GA flying above say FL100) which is deiced and has wx radar etc.

With a bit of care and hands-on management one can do a complete flight with hardly a single bump. But that’s possible only in VMC. Once you are in IMC, there could be anything inside it. One can have a good guess as to the worst case of what might be in there (by looking at IR images, radar images, sferics, even tafs/metars) but it will never be 100% certain for a prolonged flight in IMC.

Always keep decisionmaking in the cockpit.

As to how to decide whether a flight is doable given certain conditions, that’s another debate

Shoreham EGKA, United Kingdom

@Peter As far as is known, the only airborne breakup of a TB20 was in a CB in Sweden.

I believe there was also an accident about 20 years ago when TB20 departed EHBK, entered a TCu in one piece and came out of the bottom in bits

EHLE / Lelystad, Netherlands, Netherlands

A very good point you make, Peter: the key to surviving this is slowing down to VA, and try to keep attitude (not heading or altitude) but not over control.
Don’t hesitate to drop the gear even if you’re already above VLO, stay at VA.


Also you have to be a very good instrument pilot to get away with this. Not in the sense of passing an IR test (flying a procedure while doing the radio etc) but in the sense of keeping the thing the right way up in IMC when you are getting chucked around. If you lose it, especially in roll, you get a spiral dive in seconds and then – inside a nasty cloud – it’s all over. You have to really focus on the AI and maintain pitch and roll.

Shoreham EGKA, United Kingdom
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