Aviathor wrote:
That’s what is called “selective memory”, i.e you remember only what you want
The basic cloud spacing rules for VMC are really very simple. 1000 ft vertically, 1500 m horizontally in all airspace. That’s it. Additionally you need 5 km flight visibility below FL100 and 8 km at or above. I frankly don’t believe that “practically nobody” can remember that unless they don’t want to.
The only complication is in uncontrolled airspace at or below the highest of 3000 ft MSL and 1000 ft AGL where you don’t need to keep any distance to cloud — clear of cloud is enough. Additionally the national CAA may permit lower flight visibility in certain circumstances — the most important one being that your IAS is max 140 kt. (E.g. Sweden permits 3 km, or 1500 m in the traffic circuit. And even lower for helicopters.)
I, too, find the definition of VMC vs. IMC rather straightforward – much more so than many other terms that have been discussed here. There’s really nothing fuzzy about it.
The controller example illustrates a point – but it does not illustrate what VMC vs. IMC mean. It illustrates that there MAY be ambiguity by the usage of the term and in order to avoid ambiguity (always a good idea in radio communications, I reckon) you might want to spare a word or two to describe to the controller what actual conditions you’re flying in (i.e. in cloud/clear of cloud). This does not make the rather universal definitions of the terms more ambiguous. If, on the other hand, a controller tells you to remain VMC, I do believe they would like you to remain VMC, not VMCish, marginal VMC, fuzzy VMC, or anything like that.
As to the practicability of cloud distance: In the abscence of METAR or equivalent data, it is obviously impossible to clearly measure this (same applies to visibility). But
a) On most flights, you have an idea of at least the ceiling based on terminal and enroute METARS to base your judgement on (this applies to flying below the cloud, of course. Tops are harder).
b) While judging the exact distance may not be possible, it is very well possible to fly so close to cloud that you know that’s not 1000 ft and it’s also very well possible to fly so far above/below the cloud that you know it should be 1000 ft or more. So I guess good airmanship sort of dictates on which side to err?
Having said that, of course I’ve flown closer to cloud than this due to various circumstances.
The three reasons for wanting to know whether someone is VMC:
Really call for different specifications and one size doesn’t fit all for practical purposes.
The normal reason ATC ask if you are “VMC” is
VRPs are for VFR traffic, which ought to be in VMC 
Hmmm… I could not find most VRPs without a GPS, but that’s another topic e.g. here
The cloud distance rules are there for a reason — namely to make it possible to apply see and avoid. Even if FIS/ATC gives you traffic information it doesn’t help much unless you can visually acquire the traffic, which you can’t if it is hidden by a cloud. (Applies equally well to visual flight. Imagine two pilots having a bit of fun circling the same Cu very close, but in opposite directions.)
I recall one flight (in controlled airspace, class E IIRC) in and out of layered clouds at FL80. The controller gave me traffic information about unknown traffic at unknown altitude (mode A transponder, squawking 7000 apparently) a few miles away and closing. I could only hope that it was not “VFR” traffic at my level because there would have been no way for me to see in time to avoid even though it would have been possible to fly visually.
I think that the VMC/IMC concept is a little fuzzy to Brits who come to France VFR, but fly in clouds, and when queried by ATC claim they are VMC.
Airborne_Again wrote:
I recall one flight (in controlled airspace, class E IIRC) in and out of layered clouds at FL80. The controller gave me traffic information about unknown traffic at unknown altitude (mode A transponder, squawking 7000 apparently) a few miles away and closing. I could only hope that it was not “VFR” traffic at my level because there would have been no way for me to see in time to avoid even though it would have been possible to fly visually.
I dont see what difference it would have made?
This happens all the time in the UK, due to so much Mode A…
However I don’t recall getting visual with a single non mode C aircraft above about 3000ft.
It’s a particular demographic that does mode A, or non TXP.
This reminds me of a particular scene in Lewis Carrol’s “through the looking glass”.
’There’s glory for you!’
‘I don’t know what you mean by “glory”,’ Alice said.
Humpty Dumpty smiled contemptuously. ‘Of course you don’t — till I tell you. I meant “there’s a nice knock-down argument for you!”’
‘But “glory” doesn’t mean “a nice knock-down argument”,’ Alice objected.
‘When I use a word,’ Humpty Dumpty said, in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’
‘The question is,’ said Alice, ‘whether you can make words mean so many different things.’
‘The question is,’ said Humpty Dumpty, ‘which is to be master — that’s all.’
Language is a funny thing. There is everyday use, and them there are legal definitions, and thet don’t have to be the same. It only gets problematic if these realms gets mixed. ICAO and most countries have the definition that VMC are conditions which allow you to fly VFR, IMC are conditions that require you to fly IFR, and Special VFR are flown in IMC. Pilot think that VMC are conditions in which you can maintain control visually, IMC are conditions where you have to fly on instruments.
Both definitions are equally valid, we only have to be careful that we use the legal definition when it comes to air law, and vice
versa. Otherwise, wr will claim that brakes are primary flight controls, an opinon that is perfectly valid when applied to musing about what one needs to control a skittish taildragger in a gusting crosswind, but does not apply when intepreting rules.
Fuji_Abound wrote:
I dont see what difference it would have made?
If it was indeed at my altitude and I could see it, then I could avoid it.
