So......
Jeppesen/ATC/AU-501/1.2.1.4
Quote:
The position to change between QNH & 1013.2 hPa shall always be in the Standard Pressure Region on climb after passing 10,000ft and prior to leveling off, or on descent to a level in in the Altimeter Setting Region prior to entering the Transition Layer.
So in plain English, set 1013.2 at or after passing 10,000' on climb, and set QNH prior to FL110 on descent to any level at or below 10,000'
From UK AIP ENR 1.7
"When cleared for climb to a Flight Level, vertical position will be expressed in terms of Flight Level, unless intermediate altitude reports have been
specifically requested by Air Traffic Control.
When an aircraft is descended from a Flight Level to an Altitude preparatory to commencing approach for landing, ATC will pass the appropriate aerodrome QNH. On vacating the Flight Level, the pilot will change to the aerodrome QNH unless further Flight Level vacating reports have been requested by ATC, in which case, the aerodrome QNH will be set following the final Flight Level vacating report."
In general therefore, unless ATC request otherwise, you can change to STD as soon as cleared climb to a flight level, and you can change to QNH as soon as you commence descent to a cleared altitude.
Exeptions are:
You must have QNH set for take off and can't change to STD below flap retraction altitude.
At least one altimeter (e.g. the standby) should remain on QHN below MSA for terrain awareness.
that means that there are differences depending on the FIR you are flying in. Would it be safe to assume all JAA FIRs have the same rule? What about in North America? What about the rest of the world?