I know its the controller's section of PPRUNE, but as a pilot I would rather have to change QNH in the cruise or early descent when my work load is at its lowest. People always quote the day when a pressure change is 10 mb over 200nm but fail to quantify that it only happens on 35 days of the year, the rest of the time it is much less. The majority of long sectors are flown above 20,000' and it would be a mistake to design the UK air traffic sysyem around the 3 flights a day that route from EDI to LSI. The vast majoity of flights will still be cruising on STD. Of the few flights that dont, they will still take of on one QNH then land on another QNH. The only difference is they will use an intermediate QNH for cruise rather than STD. On a high pressure stable day there might be no altimter changes..... but that would also only be 35 day per year .
What is a problem is having pilots changing from STD to QNH while changing frequency at around 6,000' and the work load is at its greatest.
This excellent proposal will remove a very old but dangerous procedure. Many altitude busts have occurred because of the low TA. The much slated GA pilots will no longer be challenged by lower airspace that could be a FL or altitude with no rhyme or reason as to which it is. This could lead to fewer airspace busts.
Airspace planning will no longer have to stop outbounds at 6,000' for fear of clearing a dim and retarded pilot to climb to a Flight Level with the risk they might forget to change to STD. This will save fuel, reduce noise, increase safety through reduced workload in the cockpit and release airspace/ create more airspace for other airports traffic.
I would prefer to see 24,000' but am equally happy with 18,000'.
As a pilot I can see no down side and found it worked well in the USA in busy airspace.
bb