Use this forum to flag up examples of red tape and gold plate
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By Genghis the Engineer
I doubt very much anybody will fix this, but I feel the need for a rant.

Like most people, I fly in knots, and plan in nautical miles. Most Brits, French, Americans, etc. etc. etc. all do this.

In Europe, visibility is reported in metres or kilometres, so are horizontal cloud separation minima, approach visibility minima, etc.

In North America, visibility is reported in statute miles, horizontal cloud separation minima are given either in thousands of feet (occasionally hundreds) or in statute miles. Approach visibility minima ditto.

Just possibly, could the world be persuaded TO GIVE VISIBILITY IN NAUTICAL MILES. I can handle even my approach minima being given in decimal or quarter miles, but it would just be so much more consistent for absolutely everybody. I can't think of any instance where anybody needs visibility requirements or minima giving more precisely than to the nearest 0.1nm, which would probably make for a really easy to handle standard.

It would just make life, flying around the world, that little bit easier, for absolutely no apparent loss anywhere.

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By Irv Lee
I have been pointing this out for years in my Masterclasses. People talk about 5km or 10km as if they are good, but when it is pointed out the first is only just beyond the airfield from the edge of an atz and the second same but a matz, many are surprised as they never think of it in real terms.
Just another example of committee work by experts.
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By Irv Lee
I seem to remember it all came in from what I assumed was icao in the early 90s
General belief was metres for vis traded for height in feet between the Anglo and French worlds.
By bookworm
Genghis the Engineer wrote:Just possibly, could the world be persuaded TO GIVE VISIBILITY IN NAUTICAL MILES.

Wouldn't you run into difficulties with approach minima? What's 550 m in NM?
By johnm
I suspect the best answer would be to go metric for everything, but that won’t happen as long as the US continues to use arcane and archaic units. :twisted:
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By T67M
The USA went metric some years ago. The metric foot is exactly 30.48cm - although of course in the UK the metric foot is only 30.00cm, which has caused some minor errors... Such as spacecraft missing Mars and heading into deep space.
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By jaycee58
In the unreal world of CAA exams I've had plenty of practice of altitudes in metres and pressures in Newtons/square inch. The first is fair enough, the second should be a hanging offence!
By PaulB
Genghis the Engineer wrote:Nothing arcane about the nautical mile, it's based upon the size of the planet, and as such incredibly logical.

So is a North/South nautical mile different to an East/West one (and was the estimate of the size of the planet accurate when the unit was defined?)

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By kanga
PaulB wrote:..

So is a North/South nautical mile different to an East/West one..

well, a minute of arc of a Great Circle at high latitudes is different, yes, the earth being an oblate spheroid not a sphere as I'm sure all Forumites knew :) But the Nautical Mile was originally defined as such an arc at the Equator, IIRC.

ISTR when doing my Canadian PPL exams in '60s, before Canada went fully metric:

.. in US, wind speeds in Met and ATC reports were all in MPH; in UK they were in kt
.. in Canada, surface winds in ATC and METARs were in mph, but 'upper' winds in TAFs were in kt :roll:

.. which actually made some sense, as nearly all light aircraft, the ones most vulnerable to surface crosswinds and navigating at low levels, were US-made with ASIs calibrated in mph and POHs with performace charts printed in MPH (and with altimeters calibrated in "Hg; but so were radio/TV met bulletin pressure reports then)

And, yes, there werre 'trick questions' in the exams checking that candidates spotted and knew the differences.
By chipmeisterc
I read what seemed like a useful rule of thumb recently which described a simple means of approximating the distance to the horizon in km for every 2000ft in height, making it then very easy to estimate the distance to/from objects based on their positioning between aircraft and horizon.

This may be common knowledge but I don't recall ever being taught it. Anyway, it was so good that I quickly forgot it and can no longer find the source :lol:

Anyone familiar?
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By Genghis the Engineer
Distance in nautical miles to the visible horizon is about 1.06 times the square root of your height in feet, or something.

So at 5ft (typical eye height) about 2.4nm.

At 800ft (circuit height) about 29nm

At 2000ft 47nm.

Visibility and obstructions permitting of course. Slightly further for radio range (I think that the standard rule of thumb is about 1.2 instead of 1.06).

But at first approximation, square root of your height in feet is probably close enough.

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By PaulSS
I hate flying to the US and getting visibility in miles (especially as they normally use statute miles which bears no relevance to the commonality of aviation units). I really dislike being given 3/8 sm as it means absolutely nothing to me and I can never tell why they use such fractions. Tell me 600m and I'm good to go :D

I especially find it difficult when we're down to the low numbers. Give me an RVR of 75m for a CATIIIB approach and it's easy to understand but I literally have to sit with a conversion table open when flying in cruddy US weather. Not something I really need when establishing if approach bans are in place as I approach the outer marker/FAF(P) (in the US).