Plans for a common transition altitude in Europe has been underway for some time. Different scenarios have been described and graded, and as far as I remember, those scenarios were 7000, 10000 and 18000 ft. I seem to remember that 10.000 feet was likely to be the end result, but I am not sure.
The problem is (supposedly) cockpit confusion due to wildly variable transition altitudes. In tiny Denmark, it is 5000 ft around Copenhagen and 3000 feet in the rest of the country. And I think most airliner pilots find 3000 feet an uncomfortably low altitude to adjust altimeters for final descent if they have been leveled off at FL40.
On the other hand, a general 18.000 ft transition altitude will mean that to most propeller driven air traffic there will be a lot of QNH adjustments en-route, which will also add to cockpit workload and risk of errors.
I do not think that airspace classification (A or C) is part of that discussion.
Deleted – posted in error
On the other hand, a general 18.000 ft transition altitude will mean that to most propeller driven air traffic there will be a lot of QNH adjustments en-route, which will also add to cockpit workload and risk of errors.
I think the opposite has proven true. In keeping his altimeter accurate with respect to nature and sea level, a pilot resets it slightly every once in a while but the timing is not critical, and everybody in local radio communication is unambiguously on the same setting. If OTOH he has to transition into and out of man made flight levels on every VFR flight, there is a much greater chance that he will forget at the critical time and altitude, and much more scope for confusion with ATC – which may anyway be in simultaneous communication with aircraft on different altimeter settings. The only reason transition altitude ever existed for GA was to allow for the unavailability of airborne altimeter data – which I think is dumb assuming 20th century or better technology.
I have found a little more about Europe. I was partly right :-)
There is a Eurocontrol document as far back as 2005
https://www.eurocontrol.int/sites/default/files/field_tabs/content/documents/nm/airspace/airspace-atmprocedures-flight-deck-perspective.pdf
that concludes favorably about a “Common Transition Altitude” around 10.000 ft.
Then there is this page
https://www.eurocontrol.int/articles/harmonised-european-transition-altitude-heta
introducing the HETA = Harmonised European Transition Altitude, and which does not have the common-TA-below-10000ft-scenario, but includes a “do-nothing”-option. Our flying club responded to the stakeholder questionnaire, but whether we favored “do-nothing” or 10.000 ft I do not remember.
I have not heard anything since then and I guess we will see an NPA sometime.
On the other hand, a general 18.000 ft transition altitude will mean that to most propeller driven air traffic there will be a lot of QNH adjustments en-route
However, we have mountains in Europe higher than 10000ft, and in their vicinity you’d want your altimeter to read as close as true altitude as possible. Currently, many airways across the alps will need their lowest flight level to be closed below some (usually different) temperature. This may well mean you planned on a level that’s not available when you fly (happened to me). So I’m with Silvaire here.
And if you get more than about 4 different QNH’s during a longer flight (like Peter’s trademark 7h+ flights), then you likely have worse weather related problems than adjusting the QNH.
“If OTOH he has to transition into and out of man made flight levels on every VFR flight, there is a much greater chance that he will forget at the critical time and altitude”
I think that is partly the reason why a common TA below 10.000 ft has been abandoned. I can attest to the fact that with a TA of 3000 or 5000 ft a lot of such errors occur with VFR flights. And I guess 99+% of VFR flights are flown below FL 100.
There is a number of pros et cons for different TA’s given in the Eurocontrol papers. Curiously, one of the stated advantages for 10.000 ft is that it will eliminate the frequent R/T misinterpretation of 10.000/11.000 ft (or FL100/110 as of now). Another is that 10.000ft is an altitude often used in SOP’s e.g. for sterile cockpit, so not easy to forget. A disadvantage is that exceptions will be necessary in some mountainous areas and around some altiports.
Stated disadvantages of 18.000ft are that it is a late trigger during climb, and that several QNH updates could be necessary during descend. I admit that I have not heard US pilots complain about that, though.
Changing altimeter settings as you fly along is no big deal. Every time you contact ATC, they give you the altimeter setting as part of the check in dialog. For VFR, especially with flight following or using a weather receiver which is ubiquitous in the US, it is a no brain-er and pilots reset their altimeter almost subconsciously. There don’t seem to be may errors setting the altimeter. When you are IFR, the controller will advise if you are off altitude by more than 200 feet.
Ah but this thread was about a single class of airspace above a certain level. I understand that Europe is moving to class C above FL195.
A transition level is an entirely different thing and usually takes local geography into account.
AFAIK the 18.000 ft in the US stem from the fact, that the highest mountain in the Lower 48 is Mount Whitney in the Sierra Nevada, CA, and tops out at 14.500 ft. Some safety margin was added and thus the 18k arrived at.
As for changing altimeter settings – no big deal at all, every ATC unit (or FlightWatch if not in contact with ATC) will include the current setting in the initial call.
I check nearby ASOS’s ATIS’s anyway, as I fly along, its useful to know the surface winds in many areas. Checking the altimeter at the same time takes only a glance and a tiny twist of the knob.
