Transition Altitude/Level (TA/TL)
The TAs within the XZ division are fixed and to be at least 1000 feet above the highest ground within a 25nm radius of the airfield. Refer to the table below to get the TA for certain aerodromes or an aerodrome chart. The TL within the XZ division are not fixed and change depending on the QNH Setting.
The following table indicates the correct TL for an airport depending on the TA and the QNH Setting:
| QNH (hPa) | 3000ft | 4000ft | 5000ft | 6000ft | 7000ft | Inch. of Merc |
|---|---|---|---|---|---|---|
| 942 – 959 | 060 | 070 | 080 | 090 | 100 | 27.82 – 28.33 |
| 960 – 977 | 055 | 065 | 075 | 085 | 095 | 28.34 – 28.86 |
| 978 – 995 | 050 | 060 | 070 | 080 | 090 | 28.87 – 29.39 |
| 996 – 1013 | 045 | 055 | 065 | 075 | 085 | 29.40 – 29.92 |
| 1014 – 1031 | 040 | 050 | 060 | 070 | 080 | 29.93 – 30.46 |
| 1032 – 1050 | 035 | 045 | 055 | 065 | 075 | 30.47 – 31.03 |
| 1051+ | 030 | 040 | 050 | 060 | 070 | 31.04+ |
If you require a TA and TL for an airfield with no published TA and which is more than 25nm away from an airfield with a known QNH, use the following:
| TA | TL | |
|---|---|---|
| In VMC: | 2000ft AGL | 3000ft AGL |
| In IMC: | Use lowest safe cruising altitude for the area | Add 500ft to the lowest safe altitude |
In controlled airspace the ATC must provide the pilot with the TA and TL either by ATIS or when on request.