Hectopascals
 

Air pressure seems to be measured now in what sounds like Hectopascals. Is that different from the old measurements of QFE or QNH?

The previous unit was millibar.
Old QNH 1013 millibar
New QNH 1013 hectopascal
So it is only different name.

The CAA, against much opposition, decided a couple of years ago to implement this as it is the ICAO 'standard', otherwise it's exactly the same unit.
Pilots don't like it, controllers and FISOs don't like it, but the CAA insist on using it even though it makes RTF more complex as it doesn't 'roll off the tongue' like 'millibars'.
There is a possibility it may officially be abbreviated sometime in the future but the decision has yet to be made on this.

Yes, the Department for Pointless Change has struck again !

Isn't it only quoted over the radio for values < 1000?

Anyway bar is no longer directly related to atmospheric pressure, it was redefined equivalent to 100,000 pascals so really has no relevance anymore.

In so doing its value was reduced by 1.3%, which is why a 'standard atmopshere' is 1013 hPa and not 1000.

AFAIK, 1 bar is equal to 1000mb, which is equal to 1000hPa.
1 hPa is equal to 100 Pascals.
So 1 bar is equal to 100,000 Pascals, as you say.
But 100,000 Pascals is not equal to one hectoPascal!
100,000 Pascals is equal to 1000 hectoPascals.
Possible slip of a decimal point?

There was some french meeting redefining SI units and asking that they be called by the name of their inventor some time ago

But I thought his christian name was Blaise!!

Well if we're being picky, 1 bar is equal to 1000 mbar. The mb is a completely different unit (of area, in fact) with little or no relevance to aviation.

I was listening to ATC today when the pilot repeated back the air pressure figure without saying the word hestopastcals. ATC made the guy say the word.

So the controller was doing his job. And the word is "hectopascals". not your version!

Believe El Bunto has the right info. I believe it’s stop confusion between say 997 hectopascals and 29.97 inches. At least that’s what an ATC chap told me. It’s probably in CAP413?

Ah yes; the good old millibarn!

Thanks for the correction and Merry Christmas!

Actually, hectoPascals with a capital “P”.

I heard that a pilot used to altimeter settings in inches stupidly set digits passed as millibars on the same scale. So we've all had to change, rather than re-educate the few.

We have to say the word when the pressure is below 1000 as saying 999 can be mistaken by a US aircraft as 29x99 ! Yes I know !!!

Blame the French! Is there any metric unit commemorating someone else? Oops, I think Newtons, but who uses them?

GF

It was a very good idea to standardise and adopt ‘hectopascals’ as the unit of pressure, which most of the rest of the world already used.

The more UK-only idiosyncrasies we can eliminate the better.

While there was some resistance at the time of change, that soon disappeared. It’s just what we use now, and has had no adverse impact.

But don't hold your breath awaiting a post like that from the USA. :O

I’ll start with a :confused: , just in case you are posting in jest....then, (as someone who still uses newtons at times) off the top of my head I’d point out that the names of the basic SI units were actually deliberately chosen to commemorate the leading early researchers in their field.

From memory here is a very much none exhaustive list of metric units - yes, you can blame the French for some ....but not all of them:

Tesla, Watt, Joule, Ampere, Ohm, Volts, Curie, Hertz, Rontegen..........for the benefit if our American friends there was a fermi for a while but I think that’s no longer an official SI unit, but that reminds me of the Angstrom.......