Airfield QNH - what's the point?

[vee-tail-1]

Hmnn... If like me, you only fly day VFR/VMC at flight levels over the UK, then only two pressure settings are needed. Standard 1013.2 & QFE (or A/F QNH if you like a bit more mental arithmetic)

[Whopity]

And very soon when the Transition Altitude is raised to 18000 feet you'll be flying on the QNH.

QFF is the location value plotted on surface synoptic chart and is closer to reality than QNH, though it is only indirectly used in aviation."

QFF (next to QFE in the Q Code) was the forerunner to QNH, and was replaced because QNH is more accurate. CAP1 Q-Codes dated 1945 does not include QNH, which did not appear until a few years later.

[mm_flynn]

Originally Posted by vee-tail-1

Hmnn... If like me, you only fly day VFR/VMC at flight levels over the UK, then only two pressure settings are needed. Standard 1013.2 & QFE (or A/F QNH if you like a bit more mental arithmetic)

You are very lucky to always fly in areas where there are no airways of other CAS defined as an altitude.

For most of my VMC non-airways flying I use the altimeter to ensure avoidance of airspace (as I can see the ground to avoid that and eye ball a landing pattern so the altimeter is more of a convenience than a necessity for these)

[Maoraigh1]

Flying from Inverness, they give me RPS on leaving. Lossie then tells me to use Lossie QFE. I Just use whatever keeps the guys i'm on radio contact with happy.

[CJ Driver]

Why do they still offer RPS? As was pointed out in an earlier post by ShyTorque, RPS was promulgated in the days of no-radio cross country flying, and is (by definition) NOT the correct altimeter setting for the region, but rather is guaranteed to be a lower number than the worst-case forecast for the period. It is intended to maintain terrain clearance when all other sources of altimeter setting have been lost.

If however you are flying near, or under, any airspace (such as the Scottish TMA) for which a proper QNH is available to you, then you must set that QNH, and not the RPS. Broadly speaking, a suitable QNH is always available to you providing your radio still works. In the last 30 years I have never had a total communications failure, and therefore have never needed to use the RPS (or had the pleasure of squawking 7600, come to think of it).

[Gertrude the Wombat]

Why do they still offer RPS?

I've not heard it used, or used it myself, for decades. Without checking I wouldn't have known it still existed.

(Edit to add: this is in south eastern England, where (a) it's flat and (b) there's an airfield every few miles.)

[dont overfil]

We need fisbangwallop to comment. Scottish Info regularly offer RPS probably because of the terrain north of the TMA.

The difference between the RPS and the Ed/Gla QNH can be huge.

Notams pop up regularly if there is low pressure, warning of the increased risk of infringement.

D.O.

[bookworm]

I'm inclined to agree that airfield QNH is more useful than QFE. The point of the post was to question the wisdom of aircraft in a small area using different QNH settings.

Why would this be an issue? If the aircraft are talking to the same ATSU who is offering them either a control service or an advisory service for separation, they will use the same QNH as given by that ATSU. If they're not, what hazard arises from the use of different QNHs?

[cotterpot]

I've not heard it used, or used it myself, for decades. Without checking I wouldn't have known it still existed.

(Edit to add: this is in south eastern England, where (a) it's flat and (b) there's an airfield every few miles.)

If you are flying by Wyton you get it as part of the basic service

[A and C]

Airfield QNH is essential for accurate IFR approaches down to CAT1.

QFE is used by the military mainly to recover fast jets by PAR and keep the pilot work load down.

QFE is prohibited in some airliners (B737NG) because it upsets the EGPWS.

Horses for courses really !

[Sideslipper]

Usually, whenever I depart from my local LARS provider they wish me farewell with "Squawk 7000, Regional QNH ****".
I take it as meaning "You are on your own now mate, and if you bump into something very solid it's your fault not our's".

[GeeWhizz]

I've not heard it used, or used it myself, for decades. Without checking I wouldn't have known it still existed.

Yep still used and constantly too. Given to any aircraft that isn't going to impact other inbound/outbound flights.

Flying from Inverness, they give me RPS on leaving. Lossie then tells me to use Lossie QFE. I Just use whatever keeps the guys i'm on radio contact with happy.

Giving an aircraft the RPS before leaving the frequency is a standard thing, but more importantly its the safest by nature of it being the lowest forecast QNH for the area. By crossing the path or flying overhead a aerodrome that primarily uses QFE for all its ops, its simpler for everyone to be flying a height on the same pressure (rather than mentally working out the separation). Of course if you need to use the QNH just ask for it, you will get a QNH and should get the airfield elevation too.

I take it as meaning "You are on your own now mate, and if you bump into something very solid it's your fault not our's".

Spot on!

[mm_flynn]

Originally Posted by GeeWhizz

Yep still used and constantly too. Given to any aircraft that isn't going to impact other inbound/outbound flights.

I suspect, until recently, RPS was used by the RAF for laughs when handing off poor GA aircraft to transit under the London TMA.

Until a few years ago it was common with some military units to go from QNH to QFE for the transit then to RPS and a free call on route . . . a few miles before you then flew a couple of hundred feet below (or maybe above) the QNH define base of the TMA. I always assumed it was a plan to mess with the heads of PPLs and the TMA controllers.

[Sir George Cayley]

History & Nostalgia intrusion!

I was once told the reason why the Queen Nan How and Queen Fox Easy came about. They are, according to my source, mnemonics which equate to NH = Newquay Harbour and FE = Field Elevation.

I'd love to know if I was being fed a line or whether there is something in it.

SGC

[Aerials]

Sir George, I would expect it was Newlyn harbour, not Newquay because I believe it is the place that Mean Sea Level and tides is measured.

[flybymike]

I was always told "Field elevation" and "nautical height."

[Slopey]

Originally Posted by Gertrude

I've not heard it used, or used it myself, for decades. Without checking I wouldn't have known it still existed.

Really? I get it leaving the Aberdeen Zone, from Scottish if in a different area, London if I'm down south, and at the arrival airport at least. VFR or IFR.

[sevenstrokeroll]

the "Q" codes are quite available...just google them

and for the ease of my students on the other side of the pond...

QFE... above field elevation
QNH...normal height

and QNE...normal enroute.

[vee-tail-1]

Hmnn ... I was taught that QNH = Altitude measured from Nil Height, or sea level.

[Thud105]

This thread perfectly captures UK GA's Rules & Regs. Everyone's got an opinion, and no one knows the answer!