Setting aerodrome QFE/QNH on arrival

[tomahawk1673]

When are you supposed to set aerodrome QNH on arrival to an airfield. My instructor told me it was within so many miles or so many minutes of the airfield, which ever is sooner. Typically I can't remember these numbers.

Also setting QFE, I know you should only set it when you have the airfield in sight, but are there mile/minute limitations too? I don't recall this, but don't think there is - but I honestly can't remember :)

Thanks guys :D

[Pronto]

I don't think that there's any hard and fast rule on when to go to or from QNH or QFE.

Personally, I usually set QNH before take off (if I'm intending to leave the circuit). This eases the cockpit workload. If I'm staying in the circuit I set the QFE and leave that set.

So far as setting QFE on my return to an airfield is concerned, I usually make my initial call at what I consider to be an appropriate distance out (usually about 5 or 10 minutes, unless there are airspace restrictions which cause me to call earlier). I will get the QFE during that call and I'll set it at the same time as I start my top of descent checks.

None of the instructors I've ever flown with have commented on this practice so I assume it to meet with approval.

Any other views anyone?

Pronto

[ETOPS773]

Well,for me I change to the destination airport QNH when I`m switching to their radio station.

For example,leaving london info,to contact Southend..I`ll quickly check the ATIS and scribble down the QNH/QFE,airport information,set the QNH..then make my call to Southend,contact them with "information echo" or whatever the ATIS is at,pass my message,get my instructions..get into visual range of the airport,then set the QFE a minute or two before entering the circuit.

As for distance / time,I always make my call about 10 miles out minimum,roughly 5 minutes I guess,if not more.
Gives me plenty of time to mangage the workload,get a picture of the situation,better situational awareness..generally making things nice and slick :cool:

[bookworm]

If you're flying below the transition altitude (i.e. not using flight levels), is there any good reason for not setting your destination's QNH immediately you get it from either the ATIS or their approach frequency?

[Final 3 Greens]

Tomahawk

There is no compulsio to use QFE either (although I do.)

Many pilots fly on QNH only and allow for the field elevation accordingly.

[Pronto]

There seems to be some confusion between QNH and QFE creeping into this thread.

QFE is the barometric setting which causes the aircraft altimeter to read zero when the aircraft is on the ground at the aerodrome to which the QFE relates. Aircraft elevations when QFE is set are reported as "height". It is usual - in the UK - to land and take off with QFE set. A few years ago the RAF experimented with the US system where aircraft operated only on QNH (but with QFE available on request).

QNH is the barometric setting which causes the aircraft altimeter to show the aircraft height above sea level. This is the setting usually used for cross country flying below the transition level as it also shows your height above the chart datum. When QNH is set, aircraft elevation is reported as "altitude".

If flying above the transition level (in the UK generally 3,000 feet amsl) pilots flying in accordance with the Instrument Flight Rules are required, and pilots flying VFR are advised, to use QNE. This is a standard setting of 1013.25 hPa. Aircraft elevation is reported as "flight level".

For further discussion see Thom vol 3 at pages 113 onwards.

Pronto

[Final 3 Greens]

Pronto

Can't see any confusion between the two settings here.

If you are referring to my last posting, allowing for field elevation when flying on QNH simply entails understanding that if you are flying at 1500' (QNH) over an airfield with a 500' threshold elevation, then you are 1,000 agl and will touch down at 500' altitude, zero height.

Furthermore many commercial pilots might take issue with your assertion that it is normal to land on QFE in the UK.

You'll also find that many flight schools, such as OATS teach QNH only, inline with airline SOPS.

In the USA (as this is a global website) the altimeter setting used is QNH, although it is not called that as they have no QFE to differentiate from.

If anyone in a low lying area wonders why this is, try winding on the difference between Big Bear or Aspen (circa 7000 agl!) Also, the transition in the USA is 18,000' to standardise and take the Rockies and others into account.

[bookworm]

If flying above the transition level (in the UK generally 3,000 feet amsl) pilots flying in accordance with the Instrument Flight Rules are required, and pilots flying VFR are advised, to use QNE. This is a standard setting of 1013.25 hPa. Aircraft elevation is reported as "flight level".

That's not quite correct. QNE is not the standard altimeter setting, but rather the pressure altitude at a reference point (usually an airport), i.e. the altimeter reading with the standard 1013.25 hPa set on the subscale. See ICAO Doc 8400.

[Keef]

If I'm planning to land at the airfield, I set its QNH as soon as I get it, or as soon as I go below transition altitude, whichever is later.

If I'm arriving in nice VMC, I set QFE when I have the field in sight. If I'm arriving IFR/in IMC, I land on QNH because things get a tad busy on a missed approach, and forgetting to reset QNH from QFE can be embarrassing.

I used to use QFE for IFR approaches, and eventually convinced myself that QNH is preferable. It also means no "conversion" needed when flying in the USA.

You pays yer landing fees, and you makes yer choices.

[RotorHorn]

Just to further confuse the issue,

QFE is the barometric setting which causes the aircraft altimeter to read zero when the aircraft is on the ground at the aerodrome to which the QFE relates.

I was taught that QFE is the setting which causes the aircraft altimeter to read zero when the aircraft is above the height of the highest obstacle on the airfield....

My altimeter usually reads about -34 feet when sat on the ground at Blackpool on QFE.

As for the original thread, I usually change the pressure settings as I receive them from the different frequencies - at take off I'll have QFE from the AFIS or Tower and change to QNH when handed over to approach to depart the zone.

On the way back into the zone I'll change back to the Tower frequency and change from QNH to QFE.

That way I always remember if I'm changing frequency, I probably need to change pressure setting.

[bookworm]

I was taught that QFE is the setting which causes the aircraft altimeter to read zero when the aircraft is above the height of the highest obstacle on the airfield....

No, QFE gives you no obstacle clearance at all. The "zero" level used for measuring/calculating QFE is the aerodrome elevation, or, for threshold QFEs, the runway threshold level.

[Whirlybird]

Rotorhorn,

Of course you set everything as soon as you're given it. We rotary pilots don't have enough hands to write things down do we? ;)

So long as you remember whether you're on QNH or QFE, who really cares? I've flown here and set QFE; I've flown in the US and remembered airfield elevation; same thing really. What does it matter so long as you're comfortable with it and remember which you're doing. Though it's probably a good thing to always do it the same way, or one day you'll forget.

[Hooligan Bill]

MATS PT 1 states that ATC should pass the QFE (unless it is known that an operator uses QNH) at a convenient time before the aircraft is on final approach or before joining the visual circuit to land.

It does not really matter which you select and when, but I would advise that when flying in Controlled Airspace you ensure that you are flying in compliance with your clearance. This is particuarly important at airfields where they may be a number of mbs difference between QNH and QFE.

[Final 3 Greens]

Rotorhorn

Bookworm is quite right, the standard QFE will be based on the highest point of the airfield surface.

So you might be 34ft below that (although remembering Blackpool in the distant past, I can't recall too many big dips - maybe a few big dippers ! :D) or it might just be altimeter calibration. (isn't a difference of +/- 50 feet allowed between 2 altimeters when flying IFR?)

[Hooligan Bill]

Final 3 Greens

the standard QFE will be based on the highest point of the airfield surface.

Also not quite right, the airfield elevation which the QFE is based on is the highest point on the landing area.

[Final 3 Greens]

Bill

Fair cop! of course, our south east airfields tend to be flat anyway ;)

[Circuit Basher]

Now we're just getting down to semantics!!! ;) ;) :D

[Final 3 Greens]

Don't say that or the Pedantry Police will want play too...... :rolleyes: :rolleyes:

[FlyingForFun]

F3G said:

our south east airfields tend to be flat anyway
Speak for yourself! :eek: :rolleyes: :eek:

:D

FFF
--------------

[distaff_beancounter]

our south east airfields tend to be flat anywayOh, so that explains all my poor landings.

Having done all my basic training at Elstree, I can only do greasers on runways, that have a hump in the middle & a downslope at both ends! :D

[Final 3 Greens]

Perhaps my landings are so smooth that the runways just feel flat......

But on the other hand self delusion is a dangerous things :D

[Who has control?]

Depends on the type of landing gear, now in a bouncy Cessna which is sitting on spring steel, all landings feel rough, but in a aircraft with shock absorbers, they are all smoooooooth.
:)

As an experimant, try settin all the altimeters in in your club aircraft to a standard value, eg 1010mb, and see what they height all read. Or try setting them to O' and see what QFE they produce. I'll bet they vary by +/- 50'

[Pronto]

Ok peoples, I put my hands up! When I trained for my licence, many moons ago, the only text books available were Branson and Birch, and Ron Campbells books. Campbell didn't make any mention of following what I've always believed to be the US practice of using QNH for landing. I've now looked at a copy of Thom which does.

However, it's not only me who didn't seem to be aware of the (UK) use of QNH for landings, see http://www.chirp.co.uk/air_transport/FB45.htm The information given in that document represents what I understood to be the UK standard practice. I cannot comment on commercial operations - I have no experience. However, since this is a Private Flying forum, I wouldn't expect to have to!

Having looked at http://www.chirp.co.uk/air_transport/FB46.htm I can only accept Bookworm's correction - it seems that I've tried to be too clever with the old Q code.

I now bow out.

Pronto

[tomahawk1673]

thanks for the replies everyone.

My instructor seemed to teach me a few things the commercial way, perhaps this is one of them. So my next question is what do commercial pilots do with regard to setting QNH and Reginonal QNH on departure? Or am I asking in the wrong place?

TIA :)

[AMEX]

Commercially speaking, I depart using the QNH and once cleared to a FL then use the Standard setting.

Most commercial operators use QNH only (apart from standard of course) because on Go arouund that's how the procedure should be flown. Some chose to set the QFE for the instrument approach which is perfectly acceptable... as long as they don't forget to change the setting during the usually quite busy times following the missed approach.

As for the regional QNH, well never really use it since this is good oustide controlled airspace and below transition level. IMC that low ain't my cup of tea.
Some light aircraft operators like to save a few pounds in avoiding airways charges so tend to fly low. Luckily not the way our boss sees it. How professional is it to be bumping around at low level, dodging between airspaces with PAX down the back ? ( and remember even in a Seneca they pay a fair amount of money for the :rolleyes: privelege).

[G-SPOTs Lost]

Nope sorry chaps

QFE is the HEIGHT given above the nominated landing runway threshold. Those BPL flyers will note there is a millibar difference between QFE on RWY13 and RWY28

I also hope that you would fly around with the most accurate altimeter setting available to you at that time.

As far as JAR OPS is concerned Im pretty certain that when flying within 25 miles of a reportable QNH measuring facility then that facility will be able to offer you the most accurate altimter setting so that you can maintain accurate terrain clearnace

One of my pet hates is a student who on departure sets the regional QNH for a flight that is to remain in sight of the airfield. Regional QNH is the LOWEST forecast QNH foreseen within that hour over an area covering many thousands of square miles.

You have a responsibility to yourself and your passengers to know EXACTLY how high above msl you are.

Flight Levels also have a terrain clearance issue, normally within the UK transition level is FL30 extending I believe to FL60 within the London TMA. This is because in the UK terrain is pretty much limited to below 3000 feet. In the states where there is a much highre level of terrain diversity TL is FL180 throughout the country even thought the highest ground in Florida is a little over 300 feet

Upon leaving Majorca TL is 70 which is incidentally the MSA for that area also.

[Them thar hills]

Tom
Regional QNH v aerodrome QNH..... a minor point but if you need to remain vertically clear below SRA's etc you should use the QNH of the associated aerodrome. Regional QNH will always cause you to be higher than actual. ATC may sometimes offer the regional, if you happen to be talking to them.
Our wise CFI said don't fiddle with altimeter settings unless you really know what they should be ! And he meant it.
Commonly I'd fly on local QNH from ATIS.
And to keep winding off 40 mb before landing gets to be hard work !!
Round here the fields aren't flat, men are men and the sheep are nervous !!

Fiddle-ye-not

TTH
;)

[Gerund]

I have been reading this thread with interest. I think the key is to be adaptable and use the setting that fits the circumstance - and to be FULLY aware of the setting one is using and why.

Sitting here in Johannesburg, I have just listened to the latest Johannesburg International ATIS. It gives QNH as 1026 and QFE as 837. If you are flying privately it is very doubtful if your aircraft will be equipped with an altimeter that can be wound to 837. So if you have come over from the UK for a flying holiday to fly in SA, you will have to use QNH.

You may wish to go on a continental, and beyond, touring holiday. If you fly into Russia, the arrivals and departures will be on QFE below transition level AND altitude respectively. The 'heights' will be given in metres based on QFE and at many, even moderately high, airfields you will not be able to wind your altimeter far enought to set QFE. You will now be faced with converting heights in metres to altitudes in feet both for landing and take off.

In Kenya, due to the scarcity of reporting stations, there are not enough QNH reports to enable pilots to determine the lowest flight level which will ensure terrain clearance - lowest flight levels are based on the application of the 'climatological method'!

Interestingly, in my Aerad Flight Information Supplement (which for just a few quid makes fascinating reading) Altimeter Setting in the UK is ICAO standard....except that Aerodrome QNH will be used at or below Transition Altitude for arrival, departure, ....... No mention of QFE.

Or try Peru - QNH within Lima CTA up to 3000 ft, elsewhere 1013.2 mbs.

As to a comment made that transition altitudes are related in some way to terrain clearance............. Maybe in some countries?, but please don't try taking off, climbing through transition altitude, setting QNE and setting sail. What is the height of Snowdon? And the Andes for that matter.

It all comes down to using the setting that fits the bill and KNOWING what setting you are using, and WHY you are using it. That way private flying will be safe and fun, WHICHEVER country you are in!

:)

[BillieBob]

Oh dear, G-SPOT really is lost this time

QFE is the HEIGHT given above the nominated landing runway threshold.
Not true! QFE is the atmospheric pressure (not height) at the aerodrome elevation (OR at runway threshold) - See UK AIP GEN 2.2. Normally, if you are given QFE it relates to the pressure at the aerodrome reference point which is defined as the highest point on the landing area. If, however, you are given 'Threshold QFE', this relates to the threshold of the relevant instrument runway - See UK AIP ENR 1.7 Para 5.2.2.1

Flight Levels also have a terrain clearance issue, normally within the UK transition level is FL30 extending I believe to FL60 within the London TMA.
Not true! The Transition Level varies with atmospheric pressure, it may be FL30 one day and FL35, or FL25 the next. The Transition Altitude however is 3000ft amsl over most of the UK, except for certain areas where it is, variously, 4000ft, 5000ft or 6000ft amsl - See UK AIP ENR 1.7 Para 4.1

In the states where there is a much highre level of terrain diversity TL is FL180 throughout the country
Not true! The terms Transition Level and Transition Altitude are not used in the USA. However, FAR 91.121 describes the altimeter setting procedure and requires that, below 18000 feet MSL (c.f. Transition Altitude) the current reported altimeter setting (c.f. QNH) is used and at or above 18000 feet MSL the altimeter subscale should be set to 29.92"Hg (c.f. Standard Pressure Setting). A table of the lowest usable flight level is also provided, which varies with - guess what - Current Altimeter Setting (i.e. atmospheric pressure).

In broad terms, therefore, the US system is identical to the UK except that the 'Transition Altitude' is set at 18000 feet amsl instead of varying between 3000 and 6000 feet amsl. In both cases, the 'Transition Level' varies with atmospheric pressure.

[distaff_beancounter]

Now that you lot have totally baffled me with more facts about altimeter settings, than I had ever thought about, may I ask another question, please?

Last Saturday, I & another PPL were trying out a Garmin GPS Map 196. This has a "panel page", which amongst other instruments, shows a conventional altimeter.

When we were flying mostly under 3000ft, using airfields' QNHs, the altimeter on the GPS gave readings that were within about 30ft of the aircraft's 2 altimeters. We travelled over a route that had actual ground level heights between about 20ft and 600ft.

I assume that a GPS measures an absolute distance between the A/c & Earth's surface, and, of course, takes no account of varying barometric pressures.

BUT, where/how does the GPS measure the Earth's surface?
Mean Sea Level?
Or actual elevation under the A/c?
Or some sort of average from a database?
OR ....... ????
:confused:

[Final 3 Greens]

Distaff

At the risk of being shot down, for I am no expert, I reckon that a GPS actually works out your altitude <under> the satellites that it is triangulating from, by timing the radio signals from the satellties against an almanac database.

I am hypothesising that the GPS is set to calculate altitude from a sea level base figure.

Thus is the time for the radio signal should be x and is actually x-0.0000001 (or whatever), then the GPS calculates you are xxxx feet above sea level.

That is how I understand the horizontal triangulation to work and it seems reasonable for the vertial to be similar.

Hope this bit of saturday morning speculation helps! Anywone out there know for sure??

[G-SPOTs Lost]

Not quite so lost as you may think.... ;)

Speak to your local scare traffic controller, in the vast majority of cases ATC will give you threshold QFE without you realising. Consider Leeds Bradford where 32/14 has a 1% gradient over a 2km+ runway! giving airport QFE could be as much as 50ft out. Again its all about accurate information

Instead of swallowing the AIP and repeating it, I suggest that you look at general gist of what i was saying which was trying to encourage people to fly around on the most accurate info available, which is actually what the thread was about. Having said that you are right of course TL does alter with baro pressure, but who would want to fly at FL25??? and be wetting their pants about terrain clearnace the whole trip, that would be silly wouldn't it ????

Besides I was actually refferring to arrival not departure which incidentally is where most CFIT incidents occur. :p

How many US traffic controllers would climb an aircraft to sit on Transition level or altitude...answer none you are inviting an accident. More often than not when passing a lower altitude you would be cleared onto a flight level exceeding 18000 or FL180. It is good practice then to set standard so that altimter checks can be conducted in the climb. Only resetting them then should the controller "reclear" you to a lower sub18k, FL180 level.

Just exactly how many FAA ATPL's do you think use this chart you are refering to operationally on a daily basis, flying airplanes that will actually fly above 18000 feet

I would also suggest you check your weight & balance it must be questionable with all those AIP's on the back seat to refer to in flight.......... :rolleyes:

[Gerund]

distaff_beancounter, what an interesting thread you have running here.

I am afraid that I don't know the answer to your question about how the GPS calculates altitude, but presumably on some model of the earth - bearing in mind the damn thing isn't spherical! Using this model I assume the unit calculates altitude, ie height above msl.

This leads on to another interesting thing.

A previous poster said "You have a responsibility to yourself and your passengers to know EXACTLY how high above msl you are."

Well, this is down to interpretation; I am sure he didn't mean 'exactly'.

Altimeters are calibrated on the ISA which we all know doesn't exist in real life. When an altimeter is set to QNH we assume it should give us a reasonably accurate altitude for terrain clearance. But does it?

If our altimeters are calibrated on the ISA and this doesn't exist, what sort of errors are we looking at?

The last time I checked the two altimeters in a plane I was flying at FL250, and wound them both to the local QNH, they read within 50ft of each other. And the GPS figure? Around 1,500 feet difference (fortunately in the right direction).

Makes you think doesn't it!


:)

So what about an approach to an airfield in IMC with these sort of differences? Not a problem as the airfield observes its own barometric pressure and then adjusts this using a table of corrections (based on the ISA) to give an airfield QNH. As the altimeter is calibrated on the ISA you will have accurate altitudes for the approach using your ISA calibrated altimeter.

But dig a hole down to sea level and observe the QNH there. It will be different.

Vive la difference!

:)

[tomahawk1673]

Thanks for your help everyone, i'm not sure where my instrucctor got his numbers from, it's a shame, because he's moved away to work for an airline, and he was quite strict on them...

Scenario: If doing some local flying within 10 to 20 miles of the airfield, is it worth getting the reginal qnh if not passed and set that, along with requesting FIS?

[Gerund]

tomahawk1673 - I would advise that you set airfield QNH when you depart and leave it there until you return. Then set airfield QNH (or QFE if YOU prefer) when you contact the airfield prior to entering the circuit.

I assume you will be flying in VMC, so you can establish your own terrain clearance.

It makes sense to obtain a FIS while you fly around, but in uncontrolled airspace this is up to you. For practice, and that additional margin, why not obtain a RIS - they are so helpful and friendly.

The key thing is to have fun and enjoy the flying. Don't let all the people with their fancy theories, rhetoric, and 'must do', 'don't do' rubbish detract from the reality that flying is straightforward and enjoyable.

Yes, attention to detail is important, but if you listen too much to those who 'know', you'll miss out on the wonderful FREEDOM that flying offers!

In the immortal words of that ad, 'Just do it'.



:)

[bookworm]

d_b

The GPS calculates the position as an X, Y, Z position in 3-D space with an arbitrary reference frame. It then compares this with an ellipsoid (egg-shape) which approximately represents the surface of the earth, to give a position and altitude.

Even neglecting measurement errors, this may differ from the altitudes or elevations we know and love because the "mean sea level" we use as a reference is not a simple ellipsoid, but rather a complex shape that depends on terrain, known as the "geoid". In principle the difference (typically no more than 100 ft) could be provided in a lookup table in a GPS receiver, but usually isn't.

+-30 ft as you saw is unusually good -- not so much because of the accuracy of the GPS but rather because of the inherent errors of altimetry!

[G-SPOTs Lost]

Gerund

Wise words indeed - my apologies

[slim_slag]

How many US traffic controllers would climb an aircraft to sit on Transition level or altitude...answer none you are inviting an accident. More often than not when passing a lower altitude you would be cleared onto a flight level exceeding 18000 or FL180.

There is nothing unusable about FL180 in the US as long as regional QNH is 29.92 or above.

[Final 3 Greens]

bookworm

Thanks for that - I thought it must be something along that line!

[distaff_beancounter]

Final 3 Greens, Gerund & bookworm Thanks very much for your interesting & informative replies.

After posting my question, I realised that I was being a bit of a bozo (or technophobe) & that the base line for GPS's calculating altitude, had to be some arbitrary calculation for mean sea level.

The main thing that I have learnt from this thread, is just how many limitations & variables, & hence errors, that are just a fact of life in altimetry.

So, when in IMC, never, never take a chance on going any lower the the MSA, or MDH+50' for altimeter error, when on an instrument approach.

That is, unless your A/c has a Radar altimeter.
Now ..... I wonder how one of those works. :confused:

[Final 3 Greens]

Distaff

Just remember that a radalt only sees down (not obstacles or terrain in front)- so never go below SSA/DH/MDA per se!

;)

[tomahawk1673]

Gerund:

Thanks for your reply.

Under controlled airspace, I would definetly get FIS, or even try RIS (never had it before).

But as most of my flying is now in the open FIR, would u recommend I:


Obtain a FIS from my local ATC (if possible?)
Switch to Scottish Info to obtain a FIS
Not bother with FIS and just stay on local ATC to get the standard service (do they call it Procedural Service?)

[TheFox]

Tomahawk, you cannot get a RIS in controlled airspace as this is a service probided outside controlled airspace.

I suggest you have a look at this and it might clear up some things http://www.caa.co.uk/docs/64/ATC_Options.pdf

If you obtain a FIS from an atsu then that would probably be best, but you probably will not get traffic, and if you get a FIS from scottish you will only get info on traffic that is talking to scottish. FIS is on of the lowest kind of service you get get, its just above an alerting service and all an alerting service is that the atsu will tell someone if you stoof in.

5 Flight Information Service

5.1 A Flight Information Service (FIS) is a non-radar service provided, either separately or in conjunction with other services, for the purposes of supplying information useful for the safe and efficient conduct of flights. Under a FIS the following conditions apply:
a) Provision of the service includes information about weather, changes of serviceability of facilities, conditions at aerodromes and any other information pertinent to safety.
b) The controller may attempt to identify the flight for monitoring and co-ordination purposes only. Such identification does not imply that a radar service is being provided or that the controller will continuously monitor the flight. Pilots must be left in no doubt that they are not receiving a radar service.
c) Controllers are not responsible for separating or sequencing aircraft.

5.2 In addition to the above, controllers will, subject to workload, provide pilots with information concerning collision hazards to aircraft operating in Class C, D, E, F or G airspace when self evident information from any source indicates that a risk of
collision may exist. It is accepted that this information may be incomplete and the controller cannot assume responsibility for its issuance at all times or for its accuracy.

[distaff_beancounter]

Final 3 Greens
.... so never go below SSA/DH/MDA per se! Don't worry, I would certainly never do so, 'cos ....

- the puddle-jumpers that I fly, only have steam driven altis
- I have not got around to doing the full IR, I have only got an IMC
- I DO, have a strong sense of self preservation!
:D

[Whipping Boy's SATCO]

Sorry to get back to the question but, IMHO, the following should apply;

QFE - on approach/landing (Aerodrome or, if an instrument runway, Touchdown Zone Elevation)

Aerodrome QNH - when flying in a vicinity of an aerodrome.

Regional QNH - when transiting uncontrolled airspace.

Standard (1013.2 mbs) - when flying above the transition altitude.

All of these subject to the caveat "unless otherwise instructed by ATC". The key to all of this is that everyone knows which pressure setting they are using.

PS. As an air traffiker, I remember being asked my thoughts on the QNH vs QFE argument a few years ago by the then Air Officer Commanding Training Units (including Central Flying School). My response, that didn't go down too well, was:

"I don't give a toss sir, providing they all use the same pressure setting!"

[Chilli Monster]

WBS

Question for you from the military side (I know what a lot of civilians think - myself included).

Has Regional Pressure Setting run its course in this day and age - should we not just go onto the QNH of an adjacent airfield, whether obtained by two way comms or by listening to an ATIS?

Very relevant when you consider vast portions of the Chatham ASR should actually be flown on the London QNH as it's under the London TMA.

Enjoy EGOS - you going to be operational or training?

CM

[Whipping Boy's SATCO]

CM, I agree that it would probably be better to use the QNH of the nearest airfield. However there are two problems. Firstly, at 420 kts, the aircrew would spend half their low level life (!) trying to ascertain a pressure setting. Secondly, how do you decide which is the 'closest' airfield. Sounds silly, but you would have to have designated airfields. Otherwise, you would have some aircraft on, lets say, the East Midlands QNH with others using Langar. RPS works, although I also agree that the lateral dimensions of ASRs should mirror the CAS (TMAs) they lie under. In my neck of the woods everyone seems to get on fine using the London QNH. To be really radical, if we had satisfactory LARS coverage, the easiest thing to use would be the QNH of the particular, designated, LARS unit - no need to take a service.

One option, that may reduce confusion, would be to raise the Transition Altitude. Currently you may find aircraft floating around in the same piece of airspace on 4 pressure settings. For example, an ac in a military radar pattern may be at 3000ft QFE vs transit traffic at 3000ft QNH (airfield or RPS) and another at FL40. I certainly remember having fun controlling in a combined MATZ/CTR (FFD/BZN) where our aircraft were on QFE mbs (unless in the hold at a FL) whilst the adjacent airfield was on QNH inches. I don't have to tell you that the mental gymnastics required was potentially very confusing/dangerous. Now, if we put the TA at something reasonable (let's say a minimum of 6000ft, as in the London TMA) you take away one of the options.

The other solution is to bin QFE. The RAF tried this a few years back and it worked. The only problem was that many of the aircrew still liked to see zero on landing, consequently we changed back. Bizzare, as I have just returned from a detachment where the airfield elevation was 5871ft - try setting 800mbs on the altimeter! Needless to say, QNH was the order of the day and there were no problems.

Don't know about EGOS yet - it's just one of the options that is being floated around. If I do go, it will be the School, again.:D

[Gerund]

I wondered whether to post this or not, and then thought that, although it is not strictly applicable to the thread it might help someone doing an IMC rating who is given the question by the examiner on altitude corrections for temperature.

Although not often applicable in the UK, with winter coming and a test on a cold day, who knows what the examiner may ask?

As we know altimeters are calibrated on the ISA, which has a temperature element. If the temperature is lower than ISA then an altimeter will over read - a real life application of the 'hot to cold, don't be bold' saying.

Both Aerad and Jeppesen publish charts of values to be added to published chart altitudes in feet for instrument approaches, when the temperature is particularly low (ISA at Bournemouth 15, and a frosty morning?). They differ in the way they approach the problem (Aerad basing theirs on ISA deviations, and Jeppesen on an a/d elevation of 2000', but may be used at any aerodrome).

So just setting QNH (or QFE) for the approach may not be enough!

Hope this helps someone who may get a curved ball on their test! How nice to be able to say, with confidence, the airfield temperature is not relevant because :D ...............or is and I have made an adjustment ;), rather than :mad:

:)

[Tinstaafl]

I never use QFE. VFR or IFR.

1. Altimeter has to be reset it on a missed approach

2. Obstacle heights are referenced to SL

3. Other traffic passing through the area (apart from UK circuit & Mil. :rolleyes: ) are on some form of QNH. Even with the UK's impractical 'system', the difference between xxx feet on QNH versus Regional is less of a problem than xxx feet on QNH/regional versus QFE.

The sooner the UK ditches QFE AND establishes a common transition altitude the better.

[Whipping Boy's SATCO]

Gerund, you're absolutely right. There is an AIC about temperature correction but I couldn't find it because, unusually(!), the AIS web site is down. However, for those that are interested, follow the the following link to the US FAA explaination.

http://www.faa.gov/avr/arm/ac91-xx.doc

[tomahawk1673]

Thanks for all your replies everyone.

I've just been flicking through the PPL Confuser, and I found an Air Law question on the minimum time at which you should contact an ATSU on arrival.

The answer is 15nm or 5 minutes, which ever is greater [sooner].

I think this is what my instructor must have been on about, if I contact the unit before that time, then I must wait until 15nm or 5 minutes to set the Airfield QNH.

Does anyone think otherwise?

[LowNSlow]

I've always thought of QFE as Q Field Elevation ie the altimeter reads zero when on the ground within the limitations mentioned by other posters. QNH then translates to me as Q Nautical Height ie the altimeter reads your height above the ISA sea level which cues me to think flight level.

I used to set QFE for landing as I liked an instrument to confirm my height above the ground.
Now that I operate from a strip within controlled airspace and all approaches and departures are referenced to LTN's QNH, I use that as it is a waste of time to change it to QFE. Also I can't be bothered to do the mental gymnastics required. As you should know the elevation of the field your landing on, if it's beyond your mental capabilities to deduct this figure from that shown on your altimeter maybe you ought to ask yourself what you are doing sitting in the driving seat :D :D

[Chilli Monster]

tomahawk 1673

What you have been told is total B***S**t ;)

My radar descent chart is based on Mean Sea Level. When I descend inbounds therefore they get descended on QNH so that the reference datum is the same. Seeing as I can start descending people 40 miles out from the airfield that rather puts the "only at 5 min / 15nm" theory in the dustbin very rapidly.

CM

[Whipping Boy's SATCO]

CM, that's a pity, because my Radar Descent Chart (and the ones used at most other military airfields) is based on aerorome elevation.;)