Graham wrote:
My understanding is that the rules about boundaries are absolute. The offence, or non-offence, is where you actually are.
Cobalt wrote:
The indicated altitude (assuming correct altimeter setting).
Malibuflyer wrote:
Interesting! Two opposing statements!
Not quite. You omitted
There is nothing else they could do, and nobody can tell the difference.
from your quote. The altitudes in aviation are pressure based; the only way to measure a pressure altitude in a particular location is a pressure altimeter. The only altimeter that is in the vicinity of the aircraft is the one in the aircraft itself. This instrument is calibrated to a certain, regulated tolerance.
So sure, the boundary is an absolute altitude, it just in practice cannot be determined to any higher precision than the altimeter in front of you.
So both statements are correct.
That the instruments have a certain error is “built in the system”. Sometimes there are corrections applied, for example to minimum altitudes in cold weather, but in the absence of those, nobody is required to add the possible altimeter error to the MSA, the MDA, or any other altitude in aviation.
It is still prudent to keep. say, 100ft below controlled airspace to account for sloppy altitude keeping or the occasional distraction, though.
Peter wrote:
And there are lots of ways to get bitten. Look at this proposition. You want this CAS transit, from bottom to the top.
I seem to be missing the complexity, but if I wanted to do this transit, my plan would be to arrive at VRP Sheerness at 2500 ft (making sure I stayed well below 3500 under the class A) then do the crossing Sheerness to Northey Island (or, depending on the local situations it might be that I’m only cleared sheerness to south Woodham via Southend pier) at 2500 and after that start climbing again clear of airspace delta after passing Tiptree or so.
Obviously I can only fly it when I’m cleared for…
What catch am I missing?
Cobalt wrote:
So sure, the boundary is an absolute altitude, it just in practice cannot be determined to any higher precision than the altimeter in front of you.
That is not true. The altimeter in front of you has all kind of errors. Two plane in the same lateral position with the same altimeter setting can be vertically 100ft apart (so factually at different altitudes) even if their altimeters read the same.
If the rule is about where you actually are, the reading of the altimeter in front of you might be an indication but is for sure not the reference.
To be fair the UK has no margins for IFR inside airspace:
- LTMA vectoring happens at the base of airspace with MVA outside airspace
- IAP platforms for ILS/RNP to CAT AD are barely 500ft or 0ft inside airspace
Most ICAO countries tend to implement an ICAO standard of 1000ft separation between IFR in airspace and unknown traffic OCAS and they even keep 1000ft between unknown infringing traffic, this is not the case in UK, there is 0ft separation between IFR in CAS and unknown traffic OCAS, which makes the lowest base of airspace a “NO GO ZONE”, also on infringement, ATS would have to apply 500000ft vertical separation, which make a 1ft airspace bust a loss of separation which half of NAT traffic being told to confirm their fuel endurance or fly back to JFK…
Aside from instrument tolerances, the real question who can come up with such crappy design?
With CAIT, this is generating more noise than real concerns but it’s seems like a good way to keep ATS busy and milk few pilots, I think the safety benefit is zero or negative, especially if people start to fly on altimeters with transponders switched off (a better way to sort the problem), which does not help other GA/CAT pilots to rely on TCAS or TAS for avoidance…
Ibra wrote:
Most ICAO countries tend to implement an ICAO standard of 1000ft separation between IFR in airspace and unknown traffic OCAS and they even keep 1000ft between unknown infringing traffic, this is not the case in UK, there is 0ft separation between IFR in CAS and unknown traffic OCAS,
Ibra wrote:
Aside from instrument tolerances, the real question who can come up with such crappy design?
Typically that “crappy design” is actually celebrated by pilots in this and other forums.
It is exactly this “crap” that allows for transfers between OCAS and CAS under IFR.
If ATC has to keep 1000ft separation between IFR in airspace and the traffic OCAS, they can not clear any IFR traffic into the lowest 1000ft of CAS and therefore there is no legal way to switch vertically between CAS and OCAS.
Malibuflyer wrote:
Typically that “crappy design” is actually celebrated by pilots in this and other forums.
It is exactly this “crap” that allows for transfers between OCAS and CAS under IFR.
If ATC has to keep 1000ft separation between IFR in airspace and the traffic OCAS, they can not clear any IFR traffic into the lowest 1000ft of CAS and therefore there is no legal way to switch vertically between CAS and OCAS.
In some other countries, it is Class G – Class E – Class D/C/A.
So for a VFR traffic it is no problem, and IFR traffic usually flies with more precise instruments.
In the UK that is not the case – Class G just below Class A. There are no “shades of grey”. :)
Typically that “crappy design” is actually celebrated by pilots in this and other forums.
It is exactly this “crap” that allows for transfers between OCAS and CAS under IFR.
If ATC has to keep 1000ft separation between IFR in airspace and the traffic OCAS, they can not clear any IFR traffic into the lowest 1000ft of CAS and therefore there is no legal way to switch vertically between CAS and OCAS.
I don’t recall a single occurrence where a B747 was sent OCAS under LTMA to land at Headcorn 
I am aware of a DC3 that did that once through…
You are probably referring to artificial Echo constructs where people have to say they are VMC in the first 1000ft to legall switch VFR/IFR? or confirm VFR at MVA to legally descend on their own separation? the LTMA is very different it’s Class Alpha, no VFR inside, then Golf outside, it’s a bloody sharp design !
Where it’s problematic is the design: take east of Gatwick, MVA is 2kft, TA is 6kft, IFR route MSA is 2.4kft, VFR route MSA is 1.4kft, CAS base is 1.5kft for CTR and 2.5kft for TMA, on SRA you are flying 2kft platform, the ILS/RNP have 3kft platforms, on ATIS you hear TL = FL60
The whole thing could be made easy by pushing things a bit up 
It’s nowhere like 6kft MVA in Echo and people wondering how to get there legally on Z/Y-FPL with all VFR/IFR technicalities in Echo if there are two clouds at 3kft and no other single IFR aircraft around…
Ibra wrote:
Where it’s problematic is the design: take Gatwick, the MVA is 2kft, the TA is 3kft, IFR MSA is 2.4kft, VFR MSA is 1.4kft, CAS base is 1.5kft and 2.5kft, on SRA you are flying 2kft, on ILS 3kft, TL = FL30
@Ibra, what is more “interesting” is that to the North-East of EGKK, just East of EGKB, if you try to fly IFR OCAS between EGKB and EGTO, then:
MSA is 2400 and LTMA is 2500.
No way you can maintain a safe IFR flight while keeping 200 ft away from CAS. Or am I missing something?
Yes everything is cramped in that corner !
The Class E stuff, done many times, is 100% political: in E, IFR needs a clearance, and nobody wants to pay for the radar desks, at > £1M/year per desk for H24 cover.
The ATC business is fully indoctrinated to be on-message (visit the NATS HQ and even the potted plants there are on-message) which is why you never get serving ATCOs participating on any UK forums – except
)It works in the US, in France, etc, because they have taxpayer funded area controllers.
