Almost Trivia - When am I in cloud?

[Hidden Agenda]

What is ‘cloud’ to a VFR helicopter pilot?

An online dictionary defines cloud as: “A visible body of very fine water droplets or ice particles suspended in the atmosphere at altitudes ranging up to several miles above sea level.” So obviously I can encounter cloud at very low level, say 50 feet.

The Rules of the Air (in my local area) tell me that I can fly my helicopter VFR, below 3000 feet, as long as I remain clear of cloud and in sight of the ground or water.

How do I know when I am ‘clear of cloud’? At what point do I stop flying in low visibility and start flying in cloud? Is it at 600 metres in-flight visibility, less than 100 metres or somewhere in between?

What do you reckon?

[ConwayB]

The way I would look at it is this,

You are in cloud if:

a) it looks like a cloud and you're in it,

b) the forecast/report actually says there are clouds at your level such as ST, SC, CU, etc and your path takes you there,

c) FG is fog which is cloud that touches the ground, so technically you would be flying in ST cloud if you were flying in FG, (and before anyone jumps up and down, I am not differentiating between radiation fog, advection fog, etc... I'm just trying to make a point about cloud),

d) FU is smoke haze which is not cloud in the sense we know it but which can reduce visibility to below VMC,

e) RASH is rain showers which is not cloud (unless you are up in the ST or CU or whatever) but the RASH can reduce visibility to below VMC.

Anyway, the point is VMC means visual and flying in cloud or other obscurations usually means you are not flying in accordance with the rules of VFR.

I'm sure there are plenty of other people who would like to add some more input. The floor is yours...

[Steve76]

It suddenly occurs to me that we are training idi.....
ah forget it. Its a waste of breath.

Thank goodness that Op's Manuals were invented to motivate commonsence.
argh!

PS: you will know you are in cloud when it stops being cloud and you are suprised by the sudden stop.

[puntosaurus]

I think you're in danger of validating the CAAs current efforts to codify good airmanship with a stock visibility limit. To avoid some justified eye rolling, can I suggest your question might be better framed as "how should I fly in conditions of deteriorating visibility" ?

A technique which made sense to me was always to try and keep your forward reference point (ie your apparent horizon) the same distance away from you. If it starts coming towards you, fly towards the point you can see (as opposed to straight and level) and this will maintain your visual reference and cause you to descend. Each time you're forced to do this you slow down and when your judgement tells you it's time to stop, you make a precautionary landing.

If you have no forward reference point, you've already blown it.

Hope that helps.

[Hidden Agenda]

Conway B.

Thank for your thoughts, you have raised some interesting points.

As I said in my original post under the Rules of the Air (in my local area at least) there is no minimum defined visibility for complying with VFR so it is not possible to “reduce visibility to below VMC”.

As you can only ‘not fly in accordance with VFR’ if you are in cloud, and if as you say fog “…is cloud that touches the ground”, then is the maximum visibility that you can have and still be in fog also the flight visibility at which you enter cloud? Is that therefore the point at which you can no longer be considered VFR?


Steve76

You have taken some good pictures. You have also made some interesting posts, however I do not consider this to have been one of them.

[XT244]

Below find a bad example.
Return to the field in low level.

http://img490.imageshack.us/img490/7044/small10909737qp.jpg (http://imageshack.us)

http://img490.imageshack.us/img490/167/small10909713bh.jpg (http://imageshack.us)

[[email protected]]

Fog is defined as visibility below 1000m due to water droplets suspended in the air (condensed on hydroscopic nuclei). There fore, since fog is just cloud at ground level, you are in cloud if the visibility is less than 1000m.

[Geoffersincornwall]

I am reminded of funny site in corridor one day many years ago. Short stout co-pilot (experienced captain on new assignment) holding tall skinny captain by lapels of flight suit whose feet were two inches off the ground (captain was re-tread jet-jock with little helo IFR time) the copilot lectured the captain thus, in aussie tones,

"Listen hear you F****ing Idiot, Cloud starts in the Sky and goes up, FOG starts in the sky and goes down and YOU CAN'T FLY UNDER F****ing FOG.

I think they had just had an intresting flight back to Stavanger from the Ekofisk!

:O

[idle stop]

There is the old apocryphal RAF story of Whirlwind pilots in Cyprus who needed to log some 'Actual' instrument flying in order to progress thier service instrument ratings towards the 'Master Green' rating. Story goes theywould chase the rare bit of fluffy cloud and have a few encounters within: at 5 minutes logged per entry and exit.

[Gerhardt]

It looks like Steve76 is mired in his own cloud of ego.

This seems like a legitimate forum to ask questions without the threat of being called an idiot. Personally, I thought it was an excellent question that a lot of folks might learn from. I recall asking my flight instructor the very same question several years ago. Glad he had a little less ego and a little more tact.

[TeeS]

Hi

I Have discussed this with my daughter and apparently, if you find yourself flying inside something that looks like a sheep with no legs, you are in cloud!!

TeeS :D

[Vfrpilotpb]

Low Viz is when you can just about see, to fly that is!

You are in cloud when everything is WHITE, normally about a few seconds later your egg beater is where your arse used to be!!

Best really to avoid the all white stuff, you will have a much nicer end to your day!!!

Many regards

Peter R-B

Vfrplotpb:ok:

[NickLappos]

The question is an excellent one, and the answer is a simple one, and I think Crab got it wrong, and vfrpb got it right, IMHO.

If you are in fog, with 1000m visibility, you are not in cloud, you are in fog. The regulation is specifically written so that obscurations to visibility are not clouds.

The regulation requires that you remain "clear of cloud" so that you are steering around masses of zero vis cloud while remaining visual enough to stay right-side up, and under full control. You slow down enough to keep from hitting things, and you land if it is too bad. Think of the last time you went into cloud, what was the vis in the cloud? 1000 Meters? I doubt it, it was as close to zero as it gets, and that is a cloud, and that is what the reg means.

Of course, if you are flying around at low altitude, with 1/2 mile vis and clouds all around you, you have to ask "Why?" If you have 123 hours and are in a Robbie, you should be shot. In a US Army Black Hawk, you are at tactical VFR mins, and perhaps on your way to the landing zone, locked and loaded, and it is just a tough day at work.

[ConwayB]

Hidden Agenda, you said the following:

"How do I know when I am ‘clear of cloud’? At what point do I stop flying in low visibility and start flying in cloud? Is it at 600 metres in-flight visibility, less than 100 metres or somewhere in between?"

I would like to put in my two cent's worth...

If you stop flying in low visibility and start flying in cloud, then you are no longer in VMC and should be changing category to IFR and climbing immediately to grid or route LSALT clear of known terrain.

For a helicopter pilot, there should be virtually no excuse for inadvertantly flying into cloud (unless NVGs are involved... but that's another story). Flying into cloud should be a conscious decision either in the planning stage or in-flight when the weather unexpectedly closes in and we decide to start flying under the IFR at a time that WE, as the pilot controlling the aircraft, decide upon. And at that time, we make controlled flight inputs to climb to an appropriate altitude and continue on our journey on instruments or on top of cloud.

We are luckier than our fixed wing colleagues because we can land in the nearest clear area and wait for the weather to get better, or use our smaller turn radius to turn around and go back from whence we came if our flight qualifications, aircraft equipment or flight parameters prevent us from flying IFR.

The photographs posted earlier are good examples of when VMC is marginal at best and dangerous at worst.

Unless you're EMS or military or in another life and death situation, and your aircraft has lots of great little gadgets such as radar altimeter, GPS, AH, autopilot and all the other IFR toys... then I would be reluctant to fly in that sort of situation and prefer to be at the bar or at least on the ground slightly embarrassed... but safe. You owe this conservatism to yourself, your loved ones, the owner of the helicopter and your passengers.

Anyway, like I said, that's my two cent's worth...

I wish you safe flying and clear skies.

Conway

[Brian Abraham]

Hidden Agenda,
Steve76 may have a little difficulty recognising VFR when he sees it. Remember all those days Steve at 350 feet (our VFR limit) IMC in fog or ultra low stratus? Dont tell me you have got so old the memory is fading.
Blue Skies,
Brian
PS Frank and I are cruising the Inside Passage June 06 visiting Juneau and Ketchikan - believe you are in that area. If so will buy a beer (or two)

[Steve76]

Hey Brian,

Sure I remember 350ft ... nudge nudge wink wink :)
I learned a lot in the strait. Good to work with the pro's too. I am sorry to report that I won't be up North when you arrive. Looking for more sun further to the south for a couple of months.

I hope you and Frank are taking a couple of sheilas with you, otherwise that will create a few issues ;)
I actually think I owe you a few beers really...

Regardless, since everyone thinks I am heartless for being sarcastic at these constantly pedantic english questions; try this:

If you are doing 60kts, look for a landmark ahead and count the seconds to impact. If 30 secs pass you are in 1/2 mile vis, longer duration = better vis.
AND, check your op's manual (commonsence instruction manual) cause you will find some of the time you will be allowed to 1/4 mile.

As for the photo's of the merry English airport, I only wish we had such good vis somedays. That is a workplace reality not a heads up to go flying in that stuff.

The big question for you to think about is, how are you going to gauge all these weather rules and ceilings when you are on the top of a mountain living out of a tent for a month?

[SHortshaft]

The consensus from our corner of the bar is that for the purposes of the VFR rule:

1. Fog is not cloud; it doesn’t have a ‘Latin’ sounding name and it is usually in that part of a METAR that covers visibility not cloud - so you are not in cloud at 1,000 metres visibility.

2. Our regulator has approved an Ops Manual limit of 600 metres viz for VFR Public Transport so they don’t think that 600 metres viz is ‘in cloud’.

3. That you are no longer ‘clear of cloud’ (and therefore no longer VFR) when you are unable to fly solely by visual reference.

Therefore when you are on the top of a mountain (below 3000 feet or whatever the rule is in your area of the world) and have been living out of a tent for a month you can gauge all these weather rules and ceilings for VFR quite simply by asking yourself whether you can fly down the mountain, and not bump into anything, solely by visual reference.

Not a great idea to push the limits so close but as many of us know the real world requires us to do it sometimes.

[[email protected]]

Since the mechanism for forming cloud is the same as that for fog ie the air must be cooled below its dewpoint to allow the water vapour to condense on the microscopic nuclei in the atmosphere - then fog is cloud.
As for the visibility of 1000m, that sets the boundary between mist and fog.
Driving in fog can mean anything from a few yards visibility to several hundred metres and the same is true of flying in cloud, you just can't measure it because (hopefully) there is nothing else but cloud up there with you.

As to the original question - another driving analogy - you should only drive as fast as the visibility permits you to see a hazard and stop safely - in the air you should stop flying VFR when your ability to 'see and avoid' is degraded by weather. When are you clear of cloud? - when you are not in it!

[paco]

I believe Shawn Coyle was writing an article on this very subject for Rotor & Wing - not sure if it's out yet

Phil

[Bertie Thruster]

I agree with Crab.

When that condensation thickens to less than 1km vis, it's a cloud.

If that cloud is on the deck, its foggy.

High up in the hills, on the ground, the perception is not "in or out of cloud" but "clear, misty or foggy"!

[ConwayB]

Hello all,

I posted the reply stating that Fog is cloud that touches the ground. That's what my Meteorology instructor told me and he worked for the Bureau of Meteorology here in Australia... so naturally I took his word literally. And the definition of low level cloud is cloud that occurs from ground level to 2500m, then mid-level and high level cloud.

But I would like to add the following, which may make my original post inaccurate and could open a can of worms... but here goes.

I said that Fog was stratiform cloud that touches the ground. I would like to correct my statement and say that cloud, according the Bureau, and aviation meteorology books, is formed when a lifting mechanism causes the air to become saturated. The normal lifting mechanisms are orographic, frontal, convective or mechanical.

Fog, on the other hand, can be caused by conduction, radiation or advection.

So let me correct myself and say that cloud is the formation of visible moisture and the product of a lifting mechanism and fog is the formation of visible moisture and the product of cooling without there necessarily being a lifting mechanism.

Fog, by definition, has visibility less than 1000m and mist has visiblity greater than 1000m.

So that's the way I interpret it and what I guess is one of the reasons why fog is treated separately to cloud in forecasts and reports.

I welcome any input if I'm incorrect.

[Hidden Agenda]

ConwayB

Wow! For me at least that is good stuff.


Crab@

Interesting comments too.

But you say “…the mechanism for forming cloud is the same as that for fog…”. It would seem that might not be absolutely accurate (see ConwayB's last post).

You also say “When are you clear of cloud? - when you are not in it!” Care to say what you think “it” is in terms of visibility?

[ConwayB]

Hidden Agenda,

I think what crab was saying was that the mechanism for forming fog (ie cooling of air until it is completely saturated and moisture becomes visible) is the same as that for forming cloud (ie cooling of air [by a lifting mechanism which cools it because of the reduction in pressure and the change of temperature with altitude] until it is completely saturated and moisture becomes visible).

The same basic requirements need to be met:
cooling;
moisture;
nucleii to condense onto.

The point of mine that I was clarifying is that the result is the same but the manner in which the cooling occurs is slightly different.

Sorry for the confusion.

CB

[TeeS]

If visibility less than 1000m is cloud, how do you get a report of cloudbase - 200' rvr - 600m?

TeeS

[[email protected]]

Tees - I think we have established that to all intents and purposes, fog is cloud on the ground (my aviation met book from the Met Office agrees). However since the cloudbase is a vertical measurement from a cloudbase recorder and indicates where the thickness of the cloud (highest relative humidity probably) is sufficient to reflect the light or laser and the horizontal visibility (RVR in this case) is measured using a transmissometer over a fixed range (usually 200m) they are not stricly comparable - one is a reflected light measurement and the other a measure of the transparency of the air using a one way light transmission.

If you could measure horizontal and vertical visibility in flight you would always get variations as cloud is not a homogenous mass and has variations in relative humidity giving variations in visibility.

[Brian Abraham]

Scenerio. I live on a mountain peak X,000 feet tall. I wake in the morning and peer out the window and can't see my hand in front of my face. Is it foggy or cloudy? I would say it depends on your point of view. To me its foggy, to an observer at the mountains base it is cloud cover of Y octas with a mountain peak creating cumulo granitus.
Cheers,
Brian

[ConwayB]

Brian,

that's a very good point, and one that I was going to use to illustrate my own.

Then, when I delved a little deeper, I found that cloud is defined as the product of the cooling of air specifically due to some sort of lifting mechanism. (I didn't differentiate between this subtle difference between fog which forms because of some other cooling method such as radiation, conduction or advection).

So in your scenario, I would suggest that orographic lifting was the most likely cause of your 'fog/cloud'.

That being the case, the mountain is in cloud... and, as you so rightly pointed out, cumulus granitus if you don't maintain your LSALT.

Anyway, I had to eat crow from my previous posts. The BOM website has a glossary of meteorological terms where I discovered I was wrong in my definition of fog as being cloud that touches the ground. But now we could be accused of getting into semantics.

Say g'day to Pete T for me. He used to monster me on my check rides and would ask me questions like these on my instrument rating tests. (How's his golf swing, these days?)

Happy flying.
Conway

[[email protected]]

Brian, the Met Office answer to your question would be 'Hill Fog' which they forecast regularly in UK, usually with a visibility in hundreds of metres.

If you live in the SW of UK, the moist Tropical Maritime airmass often produces very low cloud along with 30 -40 kt winds - to an observer at sea there is a low cloud base - an observer on a 200' cliff can see less than 1000m because he is in cloud but it looks just like fog.
There is no difference between fog and cloud, other than what triggers the condensation process - it all depends on where you are viewing the cloud/fog from.

[Brian Abraham]

Since my intrest was piqued I got the old Air Ministry Meteorological “Handbook of Aviation Meteorology” out (an old, old publication) which has the following to say,
“A fog composed of water droplets (or possibly of ice crystals) may be described as a cloud on the surface. Over high ground fog may indeed be merely one or other of the usual cloud types, requiring adiabatic ascent for its foundation; the hills may protrude into a sheet of cloud or may themselves be the cause of local orographic cloud.”
It then goes on to describe Radiation Fog, Advection Fog, Steaming Fog and Frontal Fog. It says fog is used to describe vis less than 1100 yards, mist a vis between 1100 yards and 6.25 miles caused by condensed water drops.
Blue Skies (no fog – maybe a mental one though),
Brian

[[email protected]]

Brian - same book as mine but I have a 1994 version:)