Re the US system of flight levels above a comon very high transition altitude, I have the following questions;
An aircraft flies from the east coast to the west coast IFR at 14000ft. What are the laid down procedures that ensure;
a) The pilot has access in flight to the most appropriate QNH?
b) The flight does not hit a VFR flight coming the other way that hasn't reset the QNH for the past 1000nm?
Do Area Control Sectors have a QNH that they use for all flights within their sector?
When is this QNH updated and how much R/T time does it take to tell everyone on frequency and get an acknowledgement of the new QNH including some "say again"'s.
Since the QNH could be different in every sector how often do pilots change QNH on average per flight?
Finally, if the QNH in two sectors is measured at the centre of the sector, and the distance from the QNH source to the sector boundaries is 200nm, what is the worst case separatin minima of opposite direction aircraft on vastly different QNH and planned 500ft vertical separation plus some mode C error?
Of course, it looks like a great idea. However it seems to me to be an extra burden because - leaving FL350, passing FL190, set the sector (area) QNH which ensures separation from other enroute traffic then, before making the approach, set aerodrome QNH.
Seems like extra altimeter setting requirement to me.......like going back to using QFE again!
Regards,
DFC