Current QNH?

[FinnishATCO]

A question to fellow controllers around the world.

What means of updating altimeter/QNH are being used in your country/at your unit? Do you have a display showing actual altimeter/QNH values for setting altimeters available in your unit? If not, what kind of routine is used for letting pilots know the actual QNH, and what is the update frequency for the values?

Thank you for any replies in advance!

[chevvron]

A question to fellow controllers around the world.

What means of updating altimeter/QNH are being used in your country/at your unit? Do you have a display showing actual altimeter/QNH values for setting altimeters available in your unit? If not, what kind of routine is used for letting pilots know the actual QNH, and what is the update frequency for the values?

Thank you for any replies in advance!
You're an ATCO and you have to ask a question like that?
I think not.

[ShyTorque]

Seems like a reasonable question to me. Sounds like the lockdown is getting to some....

[Gonzo]

A question to fellow controllers around the world.

What means of updating altimeter/QNH are being used in your country/at your unit? Do you have a display showing actual altimeter/QNH values for setting altimeters available in your unit? If not, what kind of routine is used for letting pilots know the actual QNH, and what is the update frequency for the values?

Thank you for any replies in advance!

We have a live QNH/QFE readout which gives pressure to 0.1hPa.

As soon as the QNH or QFE moves up or down by 1hPa, our met page alerts and if it’s a QNH change then we pass that to aircraft via RT.

[Kooim00]

Here we have a live QNH feed displayed on a dedicated met screen with the feed coming from an on airport AWS

[jmmoric]

QNH/QFE with the option for an inHg-setting, for the US pilots if they require it.

Normally without any decimals, if we want to see that, it can be selected.... but the system does the rounding down just fine for us.

Should start blinking with changes, but that does not work... so we'll just keep an eye on it. Latest QNH is put on the strips when given, so rather straight forward.

[oneo]

We have an AWOS screen, updated instantly for pressure, temp, rvr etc changes.

[FlightDetent]

What is the rounding algorithm? 1 hPa equals 30 feet, give or take, and that is formally relevant.

[jmmoric]

What is the rounding algorithm? 1 hPa equals 30 feet, give or take, and that is formally relevant.

Rounding algorithm?? For what?

If it's the QNH/QFE, the decimal is always rounded down... so 1013.9 is given as 1013.

Oh, and the 1 hPa = appx. 30 feet.... that is only at ground level, due to the way an altimeter is set up, at 30.000 feet 1 hPa is roughly 70 feet. Which is the reason vertical separation is 2000 feet above FL290 (but is reduced in RVSM airspace with requirements on the altimeters of the aircraft flying there)

[FlightDetent]

QNH/QFE, the decimal is always rounded down... so 1013.9 is given as 1013. Thanks for confirming. Sorry for the simplification, it's understood that 1 hPa is around 27 feet on ISA SL but increasing going up, and thus around 30' below TA/L where pilots need it.

Going deeper, if the value as displayed in single digits decimals fluctuates between x.9 and x+1.0 what is the filtering logic? So you do not have to issue a new report for every instant change. Genuine geeky question.

[jmmoric]

Thanks for confirming. Sorry for the simplification, it's understood that 1 hPa is around 27 feet on ISA SL but increasing going up, and thus around 30' below TA/L where pilots need it.

Technically, I cannot come up with any situation where you need to convert hPa into altitude.... the 27 feet is something you learn at the academy, and in most cases never use it again (as a pilot). As a controller there are more situations where it may be relevant, but since most transition levels are now (or should be) at least 1000 feet from the transition altitude, and those calculations are done automatically, that one is not often required anymore at most ATC units.

But yes, if it keeps flipping between 1013 and 1014 (because it's flipping the decimal 3,9 and 4,0), you'd have to pass it. But those situations are relatively rare.... at least where I work.

[FlightDetent]

Things getting lost in translation, thanks for the insights provided.

As a regular (weekly basis) visitor to QFE run ATS theatres with a QNH built machine it becomes second nature and a good tool to have in the box. Not to mention some back-office calculations or the annual assessments of technical competence. :ok:

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/650x325/direction_matters_6b03bfb437516b1853d8e85ead8ad0b345911371.p ng

[42go]

I guess chevvron is feeling the pressure?

[jmmoric]

Back in my day, some 25 years ago....

It's a shame you cannot give "upvotes" here, really appreciate the reply.

I just went through the observers course... they've found out we could handle the observing from the tower, and moved the meteorologist.... (actually they fired the observer many years ago, because the meteorologist could do that)... and since the system is automated, and certified to operate without anyone doing anything anymore.... We're only supposed to poke it if anything is really wrong...

[Jim59]

I understand that the QNH for an airfield can be read directly from an instrument at the airfield.

When a Regional QNH (UK) is given how is that determined and obtained by approach controllers?

PPL

[Islandlad]

Rounding algorithm?? For what?

If it's the QNH/QFE, the decimal is always rounded down... so 1013.9 is given as 1013.

Oh, and the 1 hPa = appx. 30 feet.... that is only at ground level, due to the way an altimeter is set up, at 30.000 feet 1 hPa is roughly 70 feet. Which is the reason vertical separation is 2000 feet above FL290 (but is reduced in RVSM airspace with requirements on the altimeters of the aircraft flying there)
Doesn't that depend where your ground is?

[LastStandards]

When a Regional QNH (UK) is given how is that determined and obtained by approach controllers?

Hopefully, never, since approaches are not based on what is a rough and ready forecast (UK IAIP defines a Regional Pressure Setting as for use only when an appropriate airfield QNH is not available).

In practice the Met Office disseminate Regional Pressure Settings as their forecast for the current hour and the next hour - originally via Afpex, most of us see them nowadays on the Met Office Aviation Met site.

[grizzled]

I guess chevvron is feeling the pressure?

His reaction is a barometer of these difficult times...

[DaveReidUK]

I've always though he was a bit of a mercurial character.

[grizzled]

I've always though he was a bit of a mercurial character.

:ok: :D :D

[giggitygiggity]

Slight (and very pedantic/sad) divergence from the topic, but whilst some ATCOs are paying attention...Is - in a quiet gap of course - barking "QNH Check?" entirely on its own acceptable on a UK freq (akin to "Wind Check?") or do I need to introduce myself first then request it in the olf fashioned style?

[sambatc]

Slight (and very pedantic/sad) divergence from the topic, but whilst some ATCOs are paying attention...Is - in a quiet gap of course - barking "QNH Check?" entirely on its own acceptable on a UK freq

It would be for me, other grumpier controllers may not like it but if you need it then it's much quicker just to do as you've said

[jmmoric]

Arh, the word "check"...... way overused by some.... "check this", "check that"..... unecessary in may circumstances.