How to judge cloud separation height

[mnewbery]

Another one. If the cloud goes 45 degrees left to abeam left, however long it took in minutes to do that is the distance you were away when you finished timing.

 

So those of us doing 90 knot or 1.5 nautical miles a minute are 3 miles away from that pesky cloud if it takes 2 minutes.

 

3 nautical miles is 5430 metres

 

 

[dazza 38]

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?

True but I wouldn't bother, it is one of those rules that isn't really policeable.

 

 

[dazza 38]

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?

Why would you bother ? I have more important things to keep an eye on when flying around than worrying if this cloud or that cloud is 4800 metres away or 5200 metres away or 1000 or 1500 metres away ect.

 

 

[mnewbery]

Because it's on the exam. If I don't know it I will spend $$$$$, fail an exam and STILL not have a PPL

 

 

[ayavner]

Wasn't on my ppl exam... just have to know what the minima are. Not that there's any reason NOT to know the info, but it really wasn't that granular...

 

 

[mnewbery]

Having scattered cloud on the practical would have helped...

 

 

[dazza 38]

Everybody is different but when i'm above 3000 feet, I just use judgment/ guesstimate whether a cloud is further away than 1500 metres.

 

Each to their own though, if pilots want to be more accurate, fair enough.

 

 

[SDQDI]

I'm with you on this one Daz, I mean we all know inside when we are in the clear and when we are skirting a bit close. The more calculations you are trying to do the more likely you could inadvertently get too close, after all if the clouds are getting closer, thicker or lower you will be already working on your alternates so the workload will be high enough without complicating things.

 

 

[DWF]

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.

The move to Oktas was to make it easier for pilots and observers to determine the amount of cloud. It is much easier to divide the sky into 8ths than 10ths. 4 octas is half the sky covered in cloud. 2 octas is 1/4 (half of half), etc.

 

Decode: SKC - sky clear - 0 octas; FEW - few - 1 octa; SCT - scattered - 2-3 octas; BKN - broken - 4-7 octas; OVC - overcast - 8 octas.

 

I don't know why descriptions of the amount of cloud were adopted but the main one to remember is 'Broken' which is 4 to 7 octas, which means you can't (shouldn't) fly above that amount of cloud.

 

 

 

Tower controllers have a list of "Visibility assessment points" - locations a know distance away that they use to gain an accurate assessment of the visibility in different directions within their control zone.

 

The same thing can be applied at your home airfield/circuit area. Mt Wossname is say 9nm from the ARP and the Water Tower is 4000m North, etc.

 

Get to know these and you should be able to mentally relate these to other locations.

 

 

 

DWF

 

 

[Guernsey]

The problem is that those darn fluffy things in the sky always tend to cloud your judgement.

 

Alan.

 

 

[turboplanner]

True but I wouldn't bother, it is one of those rules that isn't really policeable.

Other than by a death sentence.

 

 

[turboplanner]

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 weather forcast is fine but conditions change?

 

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?

I agree with Facthunter that formulae can lead to a Human Factors error when you are under stress, and I think Ayavner's answer is the way to go becaise that builds the "feel" into your subconscious and you can be assessing the distance to cloud on a bad day automatically, leaving your conscious available for spotting potential Precautionary landing sites, map checking, flight planning for Alternates etc.

 

Just following on from Ayavner, 3 miles is not that much different to the length of a Downwind Leg, and you can practice a couple of three mile legs when you are out in the training area. You'll probably find that it doesn't take too much practice to get the distance into your brain, and this in turn will give you more confidence on a bad day.

 

Going back to the Downwind Leg equivalent - that's a very comfortable space to do a 180 in.

 

The picture below comes from the Visual Flight Guide

 

 

 

[dazza 38]

Other than by a death sentence.

And how is that ? We are talking about whether it is important to know if the cloud is exactly eg- 1670 metres away by wasting time mathematically working it out or guesstimating the distance at say 2000 metres. Give or take 500 metres. You're being melodramatic.

 

 

[turboplanner]

Doesn't take too long or people to lose the plot here does it.

 

CASA changed the regulations from something near impossible to get right, to 5000 metres to give ample warning that it was time to turn around, yet we have this silly discussion putting it down.

 

 

[dazza 38]

Doesn't take too long or people to lose the plot here does it.CASA changed the regulations from something near impossible to get right, to 5000 metres to give ample warning that it was time to turn around, yet we have this silly discussion putting it down.

The 5000 metres is for visibility, and up here in gods country it is normally more than 20 miles, i'm talking about the distance from your aircraft and the nearest cloud.

 

 

[ben87r]

Because it's on the exam. If I don't know it I will spend $$$$$, fail an exam and STILL not have a PPL

I would be very surprised if that was the case. Ive never heard of it before and have sat all three levels of met exams.

 

 

[turboplanner]

The 5000 metres is for visibility, and up here in gods country it is normally more than 20 miles, i'm talking about the distance from your aircraft and the nearest cloud.

Sure it's more than 20 miles, except when it isn't, as it wasn't when this multiple fatality occurred just 36 km SW of Gympie: https://www.atsb.gov.au/publications/investigation_reports/2012/aair/ao-2012-130.aspx

 

 

[turboplanner]

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

Metrication came to Australia in 1972.

 

Aviation, which had always used Nautical Miles (which may have had something to do with map projections) were given an exemption.

 

It shows you the out of control nature of CASA, when they start adding rules containing distances in metres, while retaining nautical miles.

 

 

[ben87r]

The M/KM thing is a joke.. Ive got no idea what a metre is in aviation terms and turn it into NM so i can get a time based guess, can see a min in front? Then I know ive got about 5k visibility. The states is weird also, using statute for visibility.

 

 

[facthunter]

1500 meters isn't very far. If you know of a distance in your locality which is 1500 meters or close , relate to that conceptual distance, as a basis for your estimate. You are doing this automatically doing circuits unless you do all of them at the one place or somewhere you are familiar with, when you cheat and use known features in the circuit as references. you CAN time your circuit or you can look behind at the strip and judge your distances and turn points. You also confirm your tracking accuracy this way, in the circuit.

 

( Another post sat for a day . Hope it still makes sense.) Nev

 

 

[dazza 38]

Sure it's more than 20 miles, except when it isn't, as it wasn't when this multiple fatality occurred just 36 km SW of Gympie: https://www.atsb.gov.au/publications/investigation_reports/2012/aair/ao-2012-130.aspx

None of my posts have anything to do with the weather on that particular day. This is a totally different thread.

 

 

[turboplanner]

Which day? I'm saying that although most days may be 20 nm visibility, there are still ones which will catch you out, as per the ATSB report

 

 

[Guest SrPilot]

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.

Maybe our stupidity and lack of aptitude is the reason we don't use 1500 meters despite the fact that it's an easy enough figure divisible as it is by 2, 3, 4, 5, 6, 10, 15, 20, 30, 50, etc. I'm sure I missed some but just credit it to our school system.

 

Actually, anytime something seems unsolvable simply look it up on the internet. It's gotta be there somewhere.

 

Or not.

 

http://aviation.stackexchange.com/questions/577/how-can-i-tell-how-far-i-am-from-a-cloud

 

But if it's there, and it's from the U.S., it will not be in meters, methinks.

 

 

[Old Koreelah]

...But if it's there, and it's from the U.S., it will not be in meters, methinks.

Australia metricated long ago and legislated to ban the advertising of goods in imperial measurements. Now, thanks to globalisation and American intransigence, they're infesting our shops again, and nobody is enforcing the law.

 

 

[turboplanner]

Ironically I deal with Americans involved in vehicle design and building, and, trying to be helpful was sending drawings and charts across for Australian truck design requirements using our metric dimensions and Imperial dimensions in brackets to help the Americans save time......or so I thought, until a few months later, when someone from US Engineering said "What's all this imperial crap, we've been metric for years; all the tooling is metric, the wheelbase holes are metric, and we switched years ago"