Flying with CB Activity

[Golf Alpha Whisky]

Flying has been somewhat curtailed recently due to either low cloud / mist / fog and now CB activity. I have always taken the view that CB activity in a TAF is a no no for light aircraft flying. Am I being too cautious? If there are few CB or sct CB would it be deemed safe to fly provided you steer clear of them? Or is the view that flying should be avoided if there is any CB activity around?

[Henry Hallam]

Try flying in Florida during the summer - CBs almost every day, they come and go within a couple of hours. Be aware of where they are and stay clear but it doesn't rule the day out for flying.

[Major Major]

I tend to be wary of embedded CBs showing in the forecasts - it's not so bad if you can see them and navigate around them (for which I do the old 60 degree 2 minute dog leg).

So no hard and fast rules as it depends what kind of front is causing them too.

Isol, few, or CBs around a particular front all could indicate flying can be done.

Having said that, a building Cu (not CB) on one of my first solo navs once gave me a couple of severe jolts that made me give the big 'uns a bit more respect.

[Chilli Monster]

If you can see them, go around them. It's the embedded ones when you go IMC that will bite. No reason not to fly though.

[Fuji Abound]

That is one of those questions with no yes or no answer - it depends - and the dependance ultimately comes down to experience.

At one extreme well spaced CBs that are clearly visibile and avoidable are not going to present a problem.

Clearly, at the other extreme embedded CBs, without a stormscope are more than I am willing to take on.

Of course as is usually the case with the weather there is every variation in between.

There are a number of good books that deal with met for the VFR pilot which are well worth a read and include solid discussion about flying around CB activity and how to avoid the worst of the associated problems. I would certainly invest in one of the better ones before the summer season is properly underway!

[Skin Friction]

I found out about embedded CBs once a few years back when (fortunately) flying with an instructor on a longish trip. It wasn't fun, but taught me a lot about icing, especially when the pitot heater failed :)

Has since made me very wary of days with CBs around and I think i err too much on the side of caution - have binned many a cross-country trip when they have been bubbling up. Another concern in the SE is that you often don't have much room for manoever due to controlled airspace. I do find though that CBs that seem to cover a massive area from the ground can look much more isolated once you're airborne....

Fuji - if you can recommend a specific book I'd be interested

[IO540]

You are too cautious.

It depends entirely on what other IMC there is about.

If there isn't any i.e. it is just CBs here and there, what you will have (UK/N European context, not Florida or Africa!) is some huge clouds, well scattered, with bases around 2000ft, very rarely lower than 1500ft (and rarely higher than 4000ft) and you can fly around them easily, or even under them if you want a 100-150kt car wash and get chucked around a fair bit. And the one you don't want to go under are obvious; the gap between the bottom of it and the ground is one solid column of water :)

So, VFR, not a problem, unless you get one close to departure or destination in which case you need to wait a bit. You don't want to be doing a landing anywhere near a CB (wind shear).

IFR is much worse, because you could be in IMC, and in any case under ATC control, and fly into an embedded one. I scrap any IFR flight where CBs are likely or forecast, unless the conditions as as in my VFR scenario above in which case visual avoidance is an option. There are problems with that though because of lack of online data on cloud tops especially with this kind of weather around.

In short, CBs are a non issue if you have lots of empty space to go to instead.

[Fuji Abound]

Skin Friction

Not to hand at the moment - I will PM you my favourite at the weekend.

[englishal]

Caution is a good thing where Cb's are concerned.

If you can see them, can fly around them, with plenty of room to get between them then that is ok. If you are IMC and can top them and / or have weather radar, that too is ok. Trying to fly in IMC with embeded Cb's around in Europe is Russian Roulet. In the USA ATC can give pretty good avoidance but over here it is non existant.

I think these are available to all, from AOPA ASF in the USA about thunderstorms and it gives some pretty good advice, although most is aimed at flying in the USA. Well worth a read....

http://www.aopa.org/asf/publications/sa26.pdf?wt.svl=tstorm1SA26&WT.cg_n=aa_asf

http://www.aopa.org/asf/tstormCard.pdf?wt.svl=tstorm1Card&WT.cg_n=aa_asf

[flybymike]

The main bugbears with weather diversions for CBs, heavy showers etc, is unplanned ( and unplannable) navigation changes, and resultant frequency changes etc, and controlled airspace incursion (possibly inadvertent, with all the knock-on repercussions of that)
In short, they can really cock up your whole day!

[IO540]

Well, yes, if you are going to fly in conditions that might actually require a change of route or even a change of destination, you want to be flying with a decent moving map GPS so you can see where you are at all times.

The quick back-of-a-fag-packet diversion calculation done in the PPL doesn't really work when doing it for real under pressure, especially if trying to avoid CAS.

Dead reckoning is OK if everything goes to plan but if you have to divert from halfway between two waypoints and do some random weather avoidance, the plan falls apart fast.

[SkyHawk-N]

I think these are available to all, from AOPA ASF in the USA about thunderstorms and it gives some pretty good advice, although most is aimed at flying in the USA. Well worth a read....

CBs in the USA tend to be more of a problem than those encountered in the UK, although I agree you have to be careful while flying around any CB.
The ones in the USA develop to a much bigger beast and the danger of extreme turbulance, updrafts, downdrafts and shear are that much greater (not forgetting the hail, rain and lightning!). Flying around them can be difficult due to their size, it's best to land and seek shelter until they have well and truly passed by. You don't often see anvil heads over the UK but in the US they are a regular occurence.

[bookworm]

Fuji - if you can recommend a specific book I'd be interested

Dennis Newton's Severe Weather Flying is a must-read, though it's more focused on IFR needs.

[Final 3 Greens]

The ones in the USA develop to a much bigger beast and the danger of extreme turbulance, updrafts, downdrafts and shear are that much greater (not forgetting the hail, rain and lightning!

Not to forget tornados.

I've seen one, not a reassuring sight :{

[rmac]

If CB's are about on a light IMC or VFR day, consider filing IFR even if you intend to remain in VMC as much as possible. Once you are in the system then CAS busts and navigation worries for deviations become much less of an issue.

I came back to Europe from Singapore two years ago and last summer was amazed by the level of CB activity down here in the centre. Not quite Singapore levels but heading towards it on some days.

This week we have already had a fair bit of convective activity and it is still only early May. To be honest this years annual I had storm scope fitted to back up the picture from the weather radar after a few hairy days last year.

[niknak]

I would concur with most of what has been said here, other than to remind you that on a good convective day, (late spring/mid summer, high humidity, light winds), CBs/Cu's develop very quickly and can do so behind you blocking off your point of return.

Be well prepared to divert and sit it out and, until you have the skills to navigate away from any poor weather, never ever go near or underneath a CB.

[IO540]

If CB's are about on a light IMC or VFR day, consider filing IFR even if you intend to remain in VMC as much as possible. Once you are in the system then CAS busts and navigation worries for deviations become much less of an issue.Oddly enough, I would argue that one both ways.

It's true that if on an IFR/airways flight plan, flying under ATC control, controlled airspace becomes irrelevant, so you can ask ATC for a "20-left due weather" etc and they will (usually) let you. Even national frontiers, within Europe anyway, become irrelevant, although ATC can get very grumpy if your diversion means they have to make a phone call to the other country's unit...

However, European airways routing levels (MEAs normally FL070+) normally place you initially in IMC, so the strategy is to fly VMC on top where it's nice, sunny and smooth. But you have to get there somehow, and back down again at the other end, and the IMC section cannot be avoided, and if that IMC has embedded CBs then you are in big trouble.

However, if you can do a flight under VFR in Class G (by far the most common UK private flying context) then you can avoid IMC at your leisure, and ensure that you can always see what you are flying into.

I had a very good one last year south of the Alps, where a specific IFR flight would have taken me into solid IMC with embedded CBs, big thunderstorms actually looking at the sferics data for the region, and due to the SID distance would have doubled the flight distance. Whereas a VFR flight at ~ 3000ft was in perfect VMC and smooth.

Filing "low level IFR" (below the airways i.e. not on a Eurocontrol flight plan) in the UK, which an IMC Rated pilot can do, doesn't help at all since the flight plan doesn't go anywhere of relevance. ATC units either file such flight plans as VFR (in which case nobody looks at it unless looking for the wreckage) or they file them correctly (via Eurocontrol) which usually fails because of the problems in filing IFR flight plans OCAS. And it still doesn't help because the pilot doesn't get the implied enroute IFR clearance which airways pilots get.

But yes, accurate means of navigation is a must because one must not bust airspace while flying a diversion. It also raises an issue with notams; if you bust some summer airshow...

[Africrash]

Hi

Another great book is Weather flying by Robert Buck. Seems to be regarded as on of the classics on the subject. Currently available in some london highstreet bookshops.

And I agree, CB are not a problem if you can see and avoid, we would be grounded 6 months of the year in Africa otherwise!

Best

Crash

[B2N2]

IFR: embedded? don't fly without WX radar.
VFR: avoid visually, work out their track and cross behind them, not in front.

[PlasticPilot]

Even if US CBs are more "developped" than UK ones, any CB (even junior-CB) are dangerous for light aircraft.

As someone who flew a lot where thare are also nasty, rocky, pointy things (a.k.a The Alps), I learned that deviation or circumnavigation is not always possible. Get any single CB in the Geneva area, and you can hardly fly in and out. And if I had to choose between CB and rock... well I don't.

[foxmoth]

or even under them if you want a 100-150kt car wash and get chucked around a fair bit.

I would be very careful flying under a CB, Airliners have been unable to cope with some. It is not necessarily when it is raining that you get the biggest problem, this usually happens as it starts raining heavily, that is when you get the biggest downdrafts - not to mention of course the chances of a lightening strike!:eek:

[IO540]

VFR: avoid visually, work out their track and cross behind them, not in front.

Why? The cloud moves with the wind, only. As far as the atmosphere is concerned, the cloud forms, builds up, and dies without moving along horizontally.

[172driver]

I would be very careful flying under a CB, Airliners have been unable to cope with some

Absolutely correct. You can easily get downdrafts which a small a/c simply cannot outclimb.

If at all possible, avoid CBs like the plague. And don't get fooled into thinking 'in Europe they are harmless'. They are not, and in some parts of Europe (Alps, Spanish Sierras) you can get stuff that rivals the US.

On a slightly different note, the argument about 'avoiding CBs might put you into CAS' is largely a UK problem. On the continent you generally get CAS penetration/transits very easily and ATC will usually be very accommodating if you explain why you need to do what you're doing. I've been cleared w/o any trouble through mil areas in France while slaloming through a squall line.

[rmac]

IO540

You make some very good points about limitations of MEA etc. I bet you are talking about the germanic types though ;)

Down here in the centre, where there is a lot of CB a activity in the summer, arbitrary, non terrain related MEA can be negotiated. For example from Bratislava to Wiener Neustadt the SID takes you up to 7000ft and initially away from the destination for ten miles. I guess for separation from inbound traffic. If you don't file this, Eurocontrol will reject. However after departure I would normally ask for, and get, a level off at 3000ft and a short cut. Coming back the other way however, try getting anything out of the Austrians :=

If I come back from the Slovenian coast and the weather is iffy, I will take an extra 40 miles and dog leg through Hungary, to avoid the busy and less than flexible Vienna airspace.

[IO540]

I agree Rmac that one can discard the published MEAs "due weather" - I remember transiting Germany once at FL080 keeping just below the freezing level, IMC (and icing) all the way otherwise. They didn't like it but let us do it.

However I don't think this is a good IFR strategy, because down below the cloud you have severely limited options in bad weather. Clouds have a habit of lowering and before you know it you are back in the muck, and if CBs are forecast you are back in the risk of going into one. I'd rather be on top where one can see for tens of miles and be ahead of things.

[Wrong Stuff]

VFR: avoid visually, work out their track and cross behind them, not in front.

Why? The cloud moves with the wind, only. As far as the atmosphere is concerned, the cloud forms, builds up, and dies without moving along horizontally.
Because of the relatively stronger higher level winds, any overhang or anvil will form downwind of the main body of the thunderstorm. Hail ejected from the upper levels of the thunderstorm and falling outside it in clear air will generally be from this overhang area.

[IO540]

OK, you are talking about really big CBs, with the anvil topping off at the inversion layer.

[SkyHawk-N]

OK, you are talking about really big CBs, with the anvil topping off at the inversion layer.

The anvil tops off at the tropopause. Try not to get infront of a large CB. You will probably find a strong gust front and roll clouds up to 15/20 miles ahead of it.

[DFC]

Why? The cloud moves with the wind, only. As far as the atmosphere is concerned, the cloud forms, builds up, and dies without moving along horizontally


Very true but most flights are planned to follow a ground track ( a line on the map).

If there is a CB ahead on your route and it is moving left to right over the ground then a change of track to the left will be more efficient (require less deviation from original track) that one to the right.

Never fly under a CB. The moment you decide that what you are looking at is a CB then the option to fly through or under it are gone.

If you can't go round then hold and wait for it to clear your track before proceeding.

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I would disagree that people who use visual navigation properly - i.e. map and ground will have problems. Provided that they can navigate and allow the appropriate margins.

The simple diversion techniques thaught at PPL level work very well. Can't decide if you were not taught them correctly or if you simply can't do them but in either case the problem is not with the technique.

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If in order to avoid a CB the only optionyou have is to enter (for example) the Heathrow Zone or an airway or any other controlled airspace then call and obtain a clearance - you can not be refused if it is your only safe option. i.e. the turn back option is not available. Even if you can not get the clearance and the only safe option is to enter controlled airspace then remember;

Aviate
Navigate
Communicate

Safety first, talk / write later.

Never fly through or under a CB.

Regards,

DFC

[rmac]

IO 540

You make some good points, however, if you refer back to my original post, I was recommending being in the IFR system under light IMC or VMC conditions where the CB's are visible, in order to secure sensible deviations without worrying about airspace infringements etc.

As you suggest if embedded then get on top if possible, but with the limitations that you earlier referred to i.e. possibility of running in to one on the way down.

I flew for four years in Singapore, initially was happy with on-board radar, after a few scares put in stormscope to help with identifying attenuation issues, eventually fitted water diviners and prayer mat too, just to be sure:eek:

[scooter boy]

Having CBs in the forecast just means be careful - you can still fly safely. The CB tops don't have to reach the stratosphere. They tops can can be from 10000 to 35000 (usually they are just above my svc ceiling!)

If they are not embedded then just keep your eyes open and fly around them giving them a wide berth.

If the CBs are embedded with tops below your svc ceiling then go over the top of them.

If they are isolated and the general cloud tops are below your svc ceiling then fly over the CuSc and avoid the CBs (you will see them sticking up - usually right along your route of flight and nowhere else!)

If they are widespread and embedded in a front or trough and represent a solid line that is not practical to route around then I would either plan a later departure or get as close as possible, land and let the weather pass over the top.

If they are very isolated and you have a stormscope / weather radar or preferably both then you can pick your way through but it can be rough and very icy in there.

I would recommend Richard L Collins book "Thunderstorms and Airplanes" - it dispels some of the myths about CBs.

SB

[mark147]

If the CBs are embedded with tops below your svc ceiling then go over the top of them.

Flying over the top can be a bad idea. If the CB is still developing, it can grow very rapidly (faster than you can climb). If its surface looks very crisp and well defined, only fly above it if you can stay well above or if your plane is fast enough to get of its way pretty quickly.

Lots of interesting stuff about CBs here:
http://www.ais.org.uk/aes/pubs/aip/pdf/aic/EG_Circ_2004_P_081_en.PDF

Mark

[spitfires rule]

I would say if its isolated go flying but with frontal storms or embedded stay at home. Also never fly under a storm even if you can see through it and its best to deviate to the right of a storm because this way you will have a nice tailwind to help you get out of the storm area faster.
http://www.youtube.com/watch?v=Rx6mjyKuXdg