IFR outside controlled airspace

[dont overfil]

I've just received the latest CAA notification update about possibly changing the transition level to 18000ft.

How will IFR outside controlled airspace <10000ft work if this proposal goes through?

D.O.

[2 sheds]

You mean transition altitude. Presumably semi-circular cruising altitudes, the UK-peculiar quadrantal system probably being dropped.

2 s

[sapperkenno]

It seems to work quite well in the US.

[dont overfil]

I did not put the question clearly. I was thinking of altimeter settings changing on route. I suppose the regional settings would do most of the time. As SK says it works fine in the USA. However am I right thinking there is no IFR outside controlled airspace in the rest of Europe?

It might be interesting to do the sums for near my home base where three altimeter setting regions come together. There are occasionally dramatic differences in settings between Portree, Tyne and Belfast.

D.O.

[pmh1234]

How long before EASA puts an end to IFR outside controlled airspace?:yuk:
Can you imagine this to be different between the member states. I don't think the other countries will accept this possibility in their air space

[BillieBob]

the UK-peculiar quadrantal system probably being droppedNo probably about it. Qualdrantals will cease to exist by 4 Dec 2014 when Part-SERA becomes law in the UK.

[bookworm]

I was thinking of altimeter settings changing on route. I suppose the regional settings would do most of the time. As SK says it works fine in the USA.

Discussed in a fair amount of detail in the CONOPS discussion here (http://www.caa.co.uk/docs/2257/20120131HarmonisedTAConsultationDocument.pdf).

However am I right thinking there is no IFR outside controlled airspace in the rest of Europe?

No, SERA permits it, and in fact some of the "rest of Europe" in which IFR is not currently permitted in class G is having to have a rethink.

[dont overfil]

Thanks Bookworm. That really does answer my questions and doubts. I hope you are right about IFR still being permitted in class G.

I see the ASRs will be rearranged and additional pressure reporting sites will be established. Lots of lovely new acronyms as well:8

D.O.

[aluminium persuader]

I can't see any reason why IFR ATSOCAS would change much, if at all. Where I work, the TA has recently changed from 3000 to 6000'and has had negligible impact.

With reference to RPSs, don't forget that ASRs are huge, and a QNH from a nearby airfield will be a lot more accurate and may (currently) prevent banging your head on CAS above!

[Level Attitude]

Quote:
However am I right thinking there is no IFR outside controlled airspace in the rest of Europe?
No, SERA permits it, and in fact some of the "rest of Europe" in which IFR is not currently permitted in class G is having to have a rethink.

Hmmnn....
Could be a requirement brewing for a simple to acheive, yet safe, qualification
that allows IMC(IFR) flight outside CAS.

I wonder what EASA could come up with? Probably nothing!

If only there was a current/historic Rating in a member state that might
fulfil, or form the basis, for this?

[ShyTorque]

I can't see any reason why IFR ATSOCAS would change much, if at all. Where I work, the TA has recently changed from 3000 to 6000'and has had negligible impact.

With reference to RPSs, don't forget that ASRs are huge, and a QNH from a nearby airfield will be a lot more accurate and may (currently) prevent banging your head on CAS above!

I totally agree! I fly from one ATIS to the next most appropriate one, rather than relying on the RPS which is, after all, a "best guess" forecast by a Met Man.

[bookworm]

I totally agree! I fly from one ATIS to the next most appropriate one, rather than relying on the RPS which is, after all, a "best guess" forecast by a Met Man.

I think you're missing an important aspect of this. Under SERA there is a mandatory cruising level scheme applicable above 3000 ft. The cruising level scheme, if it is to have the intended effect, has to assume that aircraft are flying on a common altimeter setting. With a 3,000 ft TA, that wasn't a problem, the common altimeter setting was 1013. With an 18k TA, there needs to be a legally correct choice of altimeter setting.

[ShyTorque]

So, please give the reference for which altimeter setting is to be used under SERA.

[chevvron]

Whatever setting is displayed on the radar of the ATC unit you're talking to?

[bookworm]

So, please give the reference for which altimeter setting is to be used under SERA.

It doesn't get a mention in either the IR or the AMC/GM. That will be interesting.

[tmmorris]

Surely the same as now if you are IFR under CAS defined as an altitude, i.e. 'the QNH of an airfield under the CAS' or words to that effect.

Tim

[bookworm]

Surely the same as now if you are IFR under CAS defined as an altitude, i.e. 'the QNH of an airfield under the CAS' or words to that effect.

And if you're flying in an area where the only controlled airspace above is the UIR above FL195?

If you're receiving a service from ATC in the vicinity of an airport, it's easy -- you use whatever QNH they give you. The tricky case is where you're talking to no one in the middle of nowhere.

[Jabawocky]

IFR OCTA?

That is how MOST of it operates down here.

Heck even Airline ops are conducted IFR, OCTA in Class G and without radar or ADSB.

Do I think that AIrline ops should be....no, more like the USA with Radar and E, but we do it all day every day down here.

[BEagle]

The issue of harmonised TA is nothing like as simple as folk might imagine.

The real problem is the Transition Layer, which is of variable vertical extent and many cruising levels will be lost at and near the TA. Not a problem with a 3000 ft TA, because not much traffic cruises that low. With a 6000 ft TA, the Heathrow holds become a problem due to traffic separation standards and inbound IFR traffic on SPS approaching the vicinity. A 10000 ft TA would lose cruising levels popular with unpressurised IFR GA aircraft - and an 18000 ft TA would lose levels popular with airlines flying short legs (e.g. Birmingham to Dublin)..... One major airline has already said that 18000 ft would cause them financial issues.

Even if an 'ideal' TA is identified, traffic cruising below the TA needs to use an altimeter setting which meets a number of requirements. The ASRs would need to be large enough to avoid frequent changes of altimeter setting but not so large that a significant pressure gradient would cause unacceptable errors, the setting must meet MoD's terrain avoidance criteria, the same setting must be used both inside and outside CAS to ensure separation is maintained..... At aerodromes, there would need to be a point at which altimeter settings are changed to/from aerodrome QNH; even if on departure that was 'on completion of noise abatement or at the ATZ boundary, whichever later' that might conflict with inbound arrivals. And what about go-arounds?

It's a very complicated topic indeed; however, NATS are well aware of the issues which affect GA and will certainly involve us in any future consultation before a final decision is made.

And before Mr GPS pops up, no, you cannot simply rely on GPS altitude!

[peterh337]

I know the USA is a totally insignificant part of the world's aviation scene, but before deriding this proposal as [various shades of] nearly impossible, has anybody asked how it works over there?

I recall being in a UK CAA presentation on GPS approaches, c. 2005, where the presenter (now a very high ranking figure in FCL) said that the CAA "found" that the FAA never analysed the reliability of GPS... So the CAA paid a bunch of consultants a load of £££ to do a GPS realibility study.

[Silvaire1]

Enroute VFR, the pilot tunes in the closest and best source of aeronautical altimeter data when he needs it. When en route IFR, he is occasionally supplied with a new setting by a controller and updates the instrument if/when its required. Having ATIS is mandatory when inbound to an controlled airport, updated just before the hour. Uncontrolled fields often have ASOS, or don't have enough traffic to matter. Mode C helps ATC independent of aircraft altimeter settings.

I find it interesting to read apparent concern with adjoining airspace having different settings. Nature doesn't work like that. Altimeter settings don't make make huge step functions at airspace boundaries unless one of the sources is out of calibration.

I suspect the real issue with uniform TA, above typical GA altitudes, is when there's not enough altimeter data available, and not enough funding to supply it reliably.

[On Track]

BEagle, it seems to me that you are looking for problems where none exists.

Countries far bigger than Britain manage perfectly well with a universal transition altitude.

Don't try to reinvent the wheel, just look at the big picture and see how it's done elsewhere.

[Gertrude the Wombat]

When en route IFR, he is occasionally supplied with a new setting by a controller
But this topic is about IFR outside "controlled airspace", where you've quite likely not got any "controller" to supply you with the occasional new setting, particularly at weekends.

[Silvaire1]

In Class G, you could surely get altimeter data from any available aeronautical source such as an airport ATIS?

[On Track]

Exactly. That's how it's done in other countries.

[BEagle]

The problem is not a harmonised TA, it's identifying the optimum harmonised TA....

Having attended the discussion session at CTC Swanwick, I can assure you that it IS a complex issue.

I find it interesting to read apparent concern with adjoining airspace having different settings. Nature doesn't work like that. Altimeter settings don't make make huge step functions at airspace boundaries unless one of the sources is out of calibration.

Consider an area with 2 adjoining altimeter setting regions. The atmospheric pressure at the boundary between the 2 might be the same, but if the atmospheric pressure is considerably different at the far edges of each area, it is obvious that, in order to have a single setting within each area, the settings for each area will need to be different....

The ideal is to minimise the number of altimeter settings needed when cruising below the TA - so the MetO was tasked to analyse data in order to identify the largest feasible area within which an acceptably significant pressure gradient might exist. Once that work has been completed, progress can be made towards the preferred solution.

In Class G, you could surely get altimeter data from any available aeronautical source such as an airport ATIS?

Not possible in large parts of the UK.....:uhoh:

[Sir George Cayley]

How would this affect an IFP which commences OCA? Staverton for instance offers RNAV (GNSS) approaches which commence in Class G.

There are TAAs for each IAF expressed as altitude, so what would one set if leaving the airway system on 1013 for the segment up to their airspace?

SGC

[Silvaire1]

Consider an area with 2 adjoining altimeter setting regions. The atmospheric pressure at the boundary between the 2 might be the same, but if the atmospheric pressure is considerably different at the far edges of each area, it is obvious that, in order to have a single setting within each area, the settings for each area will need to be different....

Of course that is true with a large pressure gradient and large altimeter setting regions. The way around it is aviation infrastructure - automated altimeter data where you need it, when you need it. We don't have official 'regions' in the US, at least none that I'm aware of.

If the data is available, it then becomes a pilot responsibility to keep his altimeter and position accurate, backed up by radar and mode C in busy areas.

The ideal is to minimise the number of altimeter settings needed when cruising below the TA - so the MetO was tasked to analyse data in order to identify the largest feasible area within which an acceptably significant pressure gradient might exist. Once that work has been completed, progress can be made towards the preferred solution.

I just checked online with my notebook, and there are 11 sources of automated altimeter data, accessible by radio or internet, within 30 miles of here. Of course you can set to airport elevation before takeoff too. An extreme (but true) example that's useful in making the point.

[mm_flynn]

I suspect the challenges in the UK are due to a combination of traditions.

1 - OCAS IFR separation used quadrantial levels, so there was only 500 feet vs 1000 feet in the US separating potentially conflicting traffic - so a difference in altimeter setting is more likely to compromise the separation (although in real life being at random levels probably reduces collision risk
2 - Large areas both laterally and vertically in the UK are OCAS and traffic densities are reasonably high. In the US, for example, OCAS (i.e. not Class E) tends to be in very remote area away from any sensible point to point navigation systems (i.e. not near a VOR or between two VORs, where you would logically expect a Class E Victor airway).
3 - The availability of and tradition of using en-route QNH is limited so 'feels' unsafe (a little like flying in IMC without separation 'feels' unsafe to the US pilot despite its statistical safety in the UK).
4 - There seems to be a UK tradition (possibly inspired by the RAF of old) of operating low level without TAWS or radar altimeters and far from (distance or time) a relevant QNH, thus the Regional Pressure Setting is a forecast highest pressure over the region and a time period - i.e. it ensures a conservative setting for terrain separation (which is only relevant if you are operating close to the ground but not visually and not landing at an airport able to provide a QNH.
5 - I suspect as well that the procedural approach of UK FIS means it is easier for them to just have a couple of RPSs rather than need to work out (based on the pilot's lame description) which QNH is most appropriate.