UK Lower Airspace transition level is 10000ft (not 18000ft as in the USA). So when climbing ie on a SID from EGKK you would reset your altimeter to 10.13mb on passing 10000ft. Your "altitute" then officially becomes a "Flight Level" (which lets ATC know you are operating on the standard pressure setting).

Yes Jay,you are correct. FL 270 is the flightlevel for switching over to Mach-reading; the pitot fed IAS becoming unreliable then.Paddy.

Squawkident,I disagree. Here's part of one of the SID charts for EGKK. It clearly states the Transition Altitude is 6,000ft. Pilots would change the altimeter when passing 6,000ft - not 10,000ft as you suggest.http://forums.avsim.net/user_files/110353.jpgCheers,

Wrong. Transition altitudes in the UK are between 3000 and 6000ft (why they would have different ones in different areas of the country beats me).Maybe in some mountainous areas it's 10k ft, but not in general.

Some charts also give the Transition Level is the lowest flight level available for use above the transition altitude.

>Yes Jay,you are correct. FL 270 is the flightlevel for>switching over to Mach-reading; the pitot fed IAS becoming>unreliable then.I think good Air-data computer can correct most errors. Piper Meridian goes to FL300 and there is no Mach meter on this aircraft and its AOM doesn't talk about IAS being unreliable above FL270.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2