Sorry if this has been asked before, did a search but couldn't find anything.

 

When I set up a flight in Radar Contact, I go into the Controller Info page and check the Transition levels are correct.  However when I 'start' RC, the T/L showing in the Display Window is always different to what is set in the Controller page.  For example I normally fly in and out of the UK so most of the time the T/L is 6000ft, but the RC Disp Window will show T/L 080 or 090 - what am I doing wrong ?

 

Glen

Nothing, you're just confusing the terms Transition Altitude and Transition Level.

 

What RC shows on the controller page is the Transition Altitude for a particular airport and this is a fixed value - the basic UK Transition Altitude is 3000ft but, as you mention, many UK airports have a TA of 6000ft. However, what RC shows in the display window is the Transition Level which is a calculated value obtained by applying the local pressure (QNH) to the Transition Altitude to give the lowest usable flight level that will provide the required separation from the Transition Altitude.

 

By definition in the UK the Transition Altitude is the altitude at and below which vertical reference is by altitude (i.e. vertical distance above sea level in thousands of feet) and the Transition Level is the flight level at and above which vertical reference is by flight level (i.e. vertical distance above the 1013Hpa pressure line). So, in the example you give (TA 6000ft, TL FL80), climb clearances up to 6000ft on the climb out will be passed as altitudes in thousands of feet and above that, the instructions will be in flight levels. It works in reverse coming down with descent clearances down to FL80 being given as flight levels and below that once again as altitudes in thousands of feet.

 

Although it's good to know, it's not really necessary to understand it as RC does the work for you. When it's time to change from QNH to standard pressure as you are cleared above the Transition Altitude or vice versa on descent below the Transition Level, you'll receive an "altimeter check" call from your co-pilot. Also, the controller will prefix his climb/descent clearances with the word "altitude" for altitudes at and below the Transition Altitude and the words "Flight Level" for levels at and above the Transition Level.

 

Pete

Hi Pete

 

Many thanks for such a detailed reply, I forgot about the difference between T/L and T/A  :blush:

 

Glen