Transition Altitude, Contact approaches..

[coolcaptain]

Hi.

I'm studying for my JAR atpls, currently holding one in Canada. From my study materials, I cannot find this information so I'm asking it here.

In the UK, where do the Flight Levels start? 3,000 ASL? I can't seem to find this answer.

Also, in the UK, is there such a thing as a contact approach? When cleared for a visual approach, must you have the field/or preceding traffic to field in sight?

Cheers.

[Gargleblaster]

Hi coolcaptain, must be nice to be such a cool to-be-captain :-)

Sorry, I'm not UK based, and only a poor PPL based in an country following ICAO/Jar docs rather closely.

BUT, generally the lowest available FL (or the Transition Level (TL)) depends on the pressure, see the local AIP for the procedure. Where I come from, ATIS says what the TL is.

Have no idea what a contact approach is, but when in a control zone (generally airspace D in ICAO speak) there are certain rules on what kind of separation is provided by ATC. When you're VFR, ATC will separate you from IFR flights and will separate you from other VFR flight through traffic information.

When you and the other traffic is VFR, whether you have the traffic in sight or not is YOUR problem, once ATC have given you the traffic information. You can always ask them where the traffic is of course, but the responsibility is yours.

[Jezzmeister]

Hi there

As far as im aware flight levels start at the height the surface is of constant atmospheric pressure (1013mb)
Im pretty sure its 500ft above the transition level; which is above the transition altitude
The transition altittude is 3000' in the uk


To be visual, two conditions have to be satisfied.
You must be in VMC conditions and maintain safe seperation from all other traffic. If not, you are flying under IFR

VMC is defined as (i quote):

Above 3000'AMSl to FL100-1500m horizontally from cloud
1000' vertically from cloud
5km visibility

at or below 3000'amsl(and below 140kt) same as for above 3000' OR clear of cloud, in sight of surface and 2km vis.

Generally, when approaching the airfield, I ask for a visual approach a few miles back when airfield is visible.
If not then i assume you are under IFR conditions and must approach under IFR.

I stand to be corrected on the above and if anyone else knows differently please reply to save us all embarrasment later down the line

Cheers

[Tinstaafl]

The UK, for some byzantine reason, doesn't have a single transition altitude. It varies depending on location & the nearest major airport.

It could be 3000. Or 6000. Or whatever is specified for the relevent airport & its airspace (including the airspace steps).

One source of info is the approach charts for the airport.

[Jerricho]

Hi Coolcaptain.

A contact approach is something that isn't used in the UK. You'll have a lot of people scratching their heads at that one (as with VFR on top ;) ). If memory serves me correctly, for a visual you have to have the runway (or approach lights?) in sight.

The transition altittude is 3000' in the uk

Not entirely correct, as the transition (QNH depending) in the London Terminal area is 6000 ft. As I have tried to forget more about millibars than you would ever know, I'll leave it to somebody else to provide the actual math regarding the actual QNH and the first actual "available" Flight Level.

[coolcaptain]

Hmm this transition layer thing is really peculiar.


Now is the transition layer based on AGL or ASL? And what's with the QFE. Do people actually set QFE on their altimeter during an approach to get height above threshold?

[what who me?]

In the UK QFE is only used by the military and by GA. You don't set QFE when you're on final for Heathrow.

Transition altitude is based on QNH (ie above sea level). If it was based on QFE it would be called a Transition Height (altitude being AMSL, height being AGL).

There is a drive towards a common transition altitude in the UK and Europe. Maybe in another decade or two.

[HEATHROW DIRECTOR]

<<You don't set QFE when you're on final for Heathrow>>

You sure could if you wanted to...

[eyeinthesky]

The transition altitude varies across the UK. Generally it is 3000ft AMSL, but in the London TMA it is 6000ft, Scottish TMA 5000ft, Birmingham 4000ft, Manchester 5000ft (I think).

The Transition LEVEL is the first usable flight level above the transition ALTITUDE. For example, using a transition ALTITUDE of 3000ft AMSL and a QNH of 1013mb, the first usable flight LEVEL will be FL35. The transition LAYER is that bit of air between the transition ALTITUDE and transition LEVEL. In this case it is 500ft thick.

Now consider a situation where the QNH is 983mb. Using 30ft/mb as a conversion, you can work out that 3000ft AMSL on 983mb is 3600ft on 1013 (20 mb difference). Therefore FL35 is not usable as it is 2900ft AMSL. So the first usable LEVEL is FL40, with a transition LAYER which is 400ft thick.

The above of course uses the UK system of Quadrantal Levels outside Controlled Airspace. If you add in the need to provide 1000ft minimum vertical separation between semicircular levels inside CAS and you increase the Transition Altitude to 6000ft but leave the QNH figures as above, you get minimum usable flight levels as follows:

QNH 1013: FL70 (actual altitude above sea level of 7000ft)
QNH 983: FL80 (actual altitude above sea level of 7400ft)

So that is why the minimum holding level for London Airports varies depending on the QNH. This is because the minimum holding level must provide AT LEAST 1000ft vertical separation above the traffic climbing to 6000ft QNH on the SIDs.

I hope this helps. The easiest way to see it is to draw the levels at various pressures on a piece of paper and see how they interact.

[Piltdown Man]

Previous replies: pretty good gen, only the last bit left. Before you are cleared for a visual approach, you will have generally confirmed that you are both visual with the airfield/runway and any other relevant traffic. Then you will hear the words "XYZ cleared visual approach, runway nn"

[180 Too Fower]

eyeinthesky.....Very well put indeed and explained, However, unless I'm going mad I work the pressure diff out to be 30mb (1013 - 983) which would be 3900ft on the 1013mb giving FL40 but with a 100 ft transition layer.

Thus: QNH 983: FL80 (Actual altitude above sea level of 7100ft)

Cheers.:ok:

[Spitoon]

I'm not going to try and work out the maths - the time I did it was for an exam and I vowed I'd try and avoid it from then on (I have a machine that does all the calculations for me nowadays)!

But there is sometimes confusion about the first FL above Transition Altitude. As I recall the definition (from the same exam) the Transition Level is the first available FL above TA. That is to say, the first FL ending in a 0 or a 5 above TA. In the UK this level is often not used because it is not separated for traffic flying just below TA - but it can be used by a controller if it suits the traffic situation.

In some other countries TL is considered to be the first FL separated from TA.

[eyeinthesky]

180:

Doh!:oh: Of course you are right! As I was typing it out I was sure I would make a mess somewhere, but didn't spot it. Thanks!

[coolcaptain]

Hey, thanks you guys.

In case anybody was wondering, a contact approach (in canada and the states, and maybe other places.. ) is a visual approach which can only be requested by the pilot. (meaning, a controller will not issue the clearance, unless you request it)

It requires you to be clear of cloud, with 1 mile ground vis, and a reasonable expectation of getting in.

Generally you would use it at an airport you were familiar with as a short-cut, so to speak.

[-IBLB-]

In the US there exist visal approaches and contact approaches, they are not the same thing.

The major difference between the two is that for a contact approach you need not have the airport (environment) in sight, which you do for a visual approach. Also as said before by coolcaptain you need to have 1mile, a good chance of getting in, and it can only be asked for by the pilot.

The contact approaches as such are not used in Europe as far as i am aware, i don't know about the rest of the world.

-IBLB-