Somebody told me years ago it was something to do with being just above the highest mountain in the USA…
AFAIK the TA (18.000’) in the US has to do with the elevation of the highest mountain. They may have put the class A base at the same altitude for convenience.
Having said that, Wikipedia lists two US mountains (including Mt. McKinley in Alaska) above 18.000 feet. If you exclude Alaska, the highest mountain in the US is only 14.505 feet (Mt. Whitney).
Mount McKinley is 20,237 feet tall in Alaska. In the CONUS lower 48 states, the highest is Mount Whitney at 14,505 feet. Class A was defined by ICAO and became a US airspace designation in 1991. Previously it was called Positive Control Area. J routes start at 18,000 MSL.
In a few years it will be 18000 in the UK
I’d guess 18,000 ft for the Class A floor was picked because its at or above the service ceiling for most planes that are flown predominantly VFR. The same altitude was then chosen for TA so the VFR traffic wouldn’t have to screw around with flight levels, and 100% of everybody talking to airport ATC (as opposed to en route ATC) would be on the same altimeter setting.
In other words, 18,000 ft for both Class A and TA was chosen for the convenience VFR cross country traffic, with talking on the radio considered relatively inconsequential (or perhaps impossible) for that traffic, and with an eye toward simplicity for those choosing to do so.
In a few years it will be 18000 in the UK
All over Europe.
Why?
In a few years it will be 18000 in the UK
I thought that the plan was Class C above FL195 all over Europe? And that is what appears to be happening in practice (but with VFR excluded from the class C!)
A big factor must be that if you allow VFR anywhere near FL200 then you will have loads of sub-5700kg traffic (most of the King Airs and a lot of bizjets) flying VFR and avoiding the route charges.
Maybe not jets (unless doing a short leg) because they still pay a heavy fuel flow price for flying that low but TPs certainly can.
I even flew in an A320 Heathrow to Brussels at FL190 all the way but there the AOC will mandate “IFR only”.
France already bans VFR in its Class D (generally FL120-FL195), presumably for this reason because why else? There is virtually zero traffic in that airspace – anywhere in Europe. I am not sure how big this area is but it comes up in notams over much of France.
It’s funny… last night I was talking to Justine about the Lancair Evolution TP. If (a) IFR was allowed in it and (b) one could freely fly all over Europe in a homebuilt then I would buy one immediately. She has had 11 years of “exposure” to all the aviation regulation crap and she asked “why can’t you just fly VFR, when most trips are not in cloud” 
She knows that only Class A bans VFR. Yeah….
Nothing IMHO will actually change. If Europe adopts FL180 as a Class A base (or whatever similar) all we will get is a formalisation of existing dodgy “private ATC policies” banning (or making stupidly difficult) VFR traffic in most of the “new” CAS. Already, in Europe, Class A is not really an issue for VFR, because only the UK and Italy have lots of it. The real issue is dodgy ICAO-breaching ATC policies [effectively] banning VFR in non Class A airspace.
I thought that the plan was Class C above FL195 all over Europe? And that is what appears to be happening in practice (but with VFR excluded from the class C!)
That is the plan as far as I know. EASA is EASA I guess, once they agree and decide on something, they have to change the rules every 5 years. In Norway VFR is allowed to FL195, so above FL195 it practically is A anyway even though it is Class C. And now they have agreed? to call Class A for Class A, which after all is in’t an entirely unreasonable thing to do 18000 feet sounds odd though.
