How to judge cloud separation height

[robinsm]

Just a question, how do you judge the distance from cloud base without actually flying to cloud base and noting it (illegal). Relying on the aviation weathjer forcast is fine but conditions change?

 

 

[ben87r]

Magic! And they fact that anyone on the ground (read CASA) is in a worse position would have a very hard time disagreeing with the PIC. Dont fly in it, keep adequate and approximate separation at all times is my best answer.

 

 

[red750]

Although I no longer fly, I was wondering the same thing. And more to the point, re horizontal separation, how can you tell if it's a large cloud at 6000m (6km), or a small cloud at 3000m? How do you assess 5000m?

 

 

[Happyflyer]

Remember under 3000 ft there is no margin if you have a radio and in sight of ground. It's just best judgement. Don't over think it, there are no measuring sticks up there.

 

 

[Guernsey]

I used to like the old VFR rules....'clear of cloud and in sight of the surface' .

 

 

[facthunter]

After a while you can judge a circuit height pretty closely without using the altimeter. so the cloud height difference will get the same. Cloud distance make an estimate and time how long it takes to get to it at your airspeed.. You develop your judgement with time and effort. Nev

 

 

[Chocolate]

Look to left or right. It's easier to judge the cloud height above you that way. Or to judge rate of descent...

 

 

[Yenn]

With broken or scattered cloud you can fly in the gaps until you see the base or the top of the clouds and check what the altimeter says, but stay in the gaps.

 

Who was the bright spark who changed from "octas" to broken, scattered etc. I can never remember which is which.

 

 

[Birdseye]

I hate to make such a stupid suggestion, but use common sense. The point of the rule is to provide enough time to see and avoid if somebody pops out of the cloud base. Beware of some CASA clown reading this thread and coming up with another idiotic requirement!

 

 

[dazza 38]

The thing is " clear of cloud " is an easy rule to comply with. Above 3000 when the rule say horizontal distance of 5000 metres. Seriously, who can judge a distance of 5000 metres.

 

 

[Happyflyer]

Horizontal distance is 1500 meters from cloud, but yes, your judgment of this distance is just a guess. No need to worry though, any CASA observer is also just guessing.

 

 

[dazza 38]

Horizontal distance is 1500 meters from cloud, but yes, your judgment of this distance is just a guess. No need to worry though, any CASA observer is also just guessing.

My apologies, I was thinking of 5000 metre visibility for some reason when I typed it.

 

 

[Guest Andys@coffs]

you take out your trusty multi $m multifrequency laser range finder, one of which penetrates the cloud and the other reflects and there you have it accurate distance between you and your canopy.....sorry you and your cloud.....

 

Its a stupid rule, there is nothing you can use as a point of reference scale so as others have said you really have no idea if the cloud is really big, but further away, or really small but close to you.

 

If the day is basically fine with not too many clouds, Id personally be looking for the shadow on the earths surface...you have much better chance of guessing with some degree of semi accuracy the range to the shadow.......of course that only works while the sun is high and not close to the horizons......

 

 

[Birdseye]

With broken or scattered cloud you can fly in the gaps until you see the base or the top of the clouds and check what the altimeter says, but stay in the gaps.Who was the bright spark who changed from "octas" to broken, scattered etc. I can never remember which is which.

Another bloody US adoption. As best I recall they used to use tenths when UK (and Europe) were using Oktas. I think its just a dumbing down - these days the US education system means a lot of Yanks can't count to ten or even 8, hence the stupid 'scattered' etc.

 

In WA quite recently the head of the BoM (or it might have been the head Bommer) decided that weather could not be described as "fine" any more. Why? Because he didn't like it.

 

 

[Birdseye]

My apologies, I was thinking of 5000 metre visibility for some reason when I typed it.

That is OK. After all, you did spell metre correctly.

 

 

[biggles5128]

When I learnt to fly many years ago I can recall an instructor saying if you hold your arm at full length your thumb will represent 500 ft below cloud when flying straight and level. This was only a rough guide but as good as any guess.

 

 

[facthunter]

Those distances are there because they have to have a figure if someone asks. probably ICAO sourced Your judgement will improve with practice. As for height .. IF you have to make an outlanding it is likely you won't know the exact height of the terrain so judging circuit heights is a good skill to have. Nev

 

 

[Guernsey]

When I learnt to fly many years ago I can recall an instructor saying if you hold your arm at full length your thumb will represent 500 ft below cloud when flying straight and level. This was only a rough guide but as good as any guess.

That's a good one to use as 'a rule of thumb'.

 

Alan.

 

 

[ayavner]

5000 metres is close to 3 miles, could you use your normal sight picture of "3 mile final" to roughly judge that distance from a cloud?

 

 

[facthunter]

I think the original distances were in miles and "metrified" and rounded up.. Whatever works for you. It's often the small thing close up or a larger one further away? issue. I still get caught out on the larger distances Over say 20 km's. That's what a stormscope or weather radar is for because I'm talking of systems rather than individual clouds.. Nev

 

 

[mnewbery]

5000 metres away is 200 seconds at 25 metres per second, 90km/h or 48KTAS. Double the speed halves the time.

 

If at 48KTAS a cloud appears to move from 45 degrees in front of your left wing to abeam your left wing in more than 100 seconds, it's more than 5000 metres away. If not, it's closer, assuming you are straight, level and cruising.

 

I don't have a PPL and I know this. It's also in my PPL syllabus.

 

Once you know the horizontal distance, going from one hand span above the glare shield to two hand spans is roughly 5 degrees. We know your descent angle is 3 degrees at 100 knots and 500 feet per minute or 48 knots and 240 feet per minute. So if the cloud in front of you goes up the screen by a hand span a minute and it's in front not above you ... Maths. ... At 48 knots it is 400 feet above you. At 100 knots it's 830 feet above you.

 

Excuses for certificated pilots not knowing this? Anyone?

 

 

[facthunter]

Well there you go. Been flying for 55 years and didn't know those formula's. If you didn't have much else to do and think about it might just work. Just out of curiosity, what syllabus is that in?

 

My excuse? well I have seen a lot of pilots who use numbers for most everything and I'm not sure it is the asnwer. Nev

 

 

[ayavner]

anyway, the question was "how to judge", not "how to calculate in real time". But no such thing as bad info, good to know mnewbery!

 

 

[facthunter]

It's all a question of priorities. There are a lot of things you must get exactly right. Approach speed descent profiles holding speeds weight and balance etc

 

On a normal flight there are plenty of things to keep your mind occupied. Map reading track keeping fuel monitoring. next position, radio frequencies. and lots more including looking for other traffic, birds etc. .

 

I don't mind having these ways of calculating things . Not doing it and needing to have an excuse bothers me. It just isn't that important to get it dead right. Humans have a great ability to develop ways of assessing things. To be aware of the total situation is important in aviation. Don't concentrate in any one thing to the neglect of something more important. That's my point.Nev.

 

 

[mnewbery]

Well there you go. Been flying for 55 years and didn't know those formula's ... Just out of curiosity, what syllabus is that in?

Mine. The bit where it says go and buy a Jeppesen E6B then do the sample questions on time and distance to a VOR station on page 20.

 

Same maths.