Hectopascals

[Thrush]

HPa

its all to do with the US habit of knocking off the “2” so 29.91 becomes 991 on the RT.... There was an Airprox a while ago in the Shetland Isles between a US crew in a Kimg Air and an ATR. That’s what caused it all, I’m told. The AAIB report refers.
Having said that, I went to SNN recently and the atco asked us what units we were using. Mb obv....! Well, we were tempted to say it for a bit of sport but remained professional with HPa.

[faoiarvok]

Originally Posted by Thrush

Having said that, I went to SNN recently and the atco asked us what units we were using. Mb obv....! Well, we were tempted to say it for a bit of sport but remained professional with HPa.

Yep, we’re required to say it even above 1000, plus we add a zero if below 1000: “Zero Niner Niner Seven hectoPascals”

The result of a number of level busts including a couple where terrain was a factor, from 99X being misunderstood as 29.9X

[chevvron]

There was a suggestion a couple of years ago that an abbreviation of 'hectopascals' might be looked into and agreed, but I've heard nothing since.

[meleagertoo]

Originally Posted by chevvron

There was a suggestion a couple of years ago that an abbreviation of 'hectopascals' might be looked into and agreed, but I've heard nothing since.

There is always millibars, a universally-used unit that we all understand and can relate to, unlike the bizarre, meaningless Eurobabble hector-pastilles.

Oh? What? Were they?

Well why the digamma did they change it then? That is not progress.

[DB6]

Millibars? Nah, not enough syllables .

[ZOOKER]

DB6,

We're lucky........It could have been Gay-Lussac who did the pressure experiments......Or even worse, Avogadro.

[ZOOKER]

Imagine if there had been more recent research into pressure by Prof. Brian Cox.

'Hectocox'? Or 'Hectocoxes'.

[chevvron]

Originally Posted by meleagertoo

There is always millibars, a universally-used unit that we all understand and can relate to, unlike the bizarre, meaningless Eurobabble hector-pastilles.

Oh? What? Were they?

Well why the digamma did they change it then? That is not progress.

Regretfully hectopascals is an ICAO SARP, not an EU requirement. Nobody knows why ICAO decided on hPa instead of mb especially as the value is the same.

[LookingForAJob]

Nobody knows why ICAO decided on hPa instead of mb especially as the value is the same.

Not strictly true. ICAO has chosen - with a small number of well defined exceptions - the International System of Units to be used as the standard system of units of measurement for all aspects of international civil aviation air and ground operations. This makes some sense - why pick/develop/use something else when the vast majority of States worldwide (although, notably, not the US) have agreed to use SI units. By practise and general agreement the units are given names related to scientists whose work was related to the element being measured; for pressure the work of Blaise Pascal was selected (perhaps interestingly, the same Pascal after whom the computer programming language is named). ICAO, since its inception, has sought to harmonise the units of measurement used in aviation - originally it recognised five different sets of units that were used globally - and adopted a harmonised set of units based on SI in 1979. In 1984 ICAO States agreed that the days of the bar were numbered and set the end of 1985 as the final date that the bar would be used in aviation. The UK held out against the change for some time and continued to use the millibar for met reports and related purposes - clearly there are a few people on this form who think this is a good thing although personally I tend to find more important things to get excited about and got used to using hPa within a day or two of their eventual mandate in UK ATC. Oh, and just in case the final bit of the puzzle is still not obvious, 'hecto' is the SI prefix for hundreds of things.

[ZOOKER]

Thank heavens we're still using feet for all things vertical. Long may it continue to be so.

[meleagertoo]

Since (on an appropriate scale) metric aircraft use milimetres to measure length, mililitres to measure volume, miliamps to measure current, milivolts in the electronics, miliTeslas in magnetic fields, and above all pressure in bars it seems a completely retrograde step to suddenly divert from this logical and self-evident progression to abandon milibars in favour of the (to most) largely meaningless hectopascal, be it an SI unit or not.

To me, progress that ain't.