When climbing to the cruising altitude you should switch to the standard pressure setting when passing through the transition altitude of the departure airport. Similarly during the descent you should switch back to local QNH pressure setting when you are descending through the transition level on the way to your destination airport.
When you have not switched to STD pressure setting above the transition altitude during climb the pressure setting starts flashing.
- Pull the pressure setting knob on the EFIS control panel to set standard pressure barometric reference (Std)
During the descent when you have not switched back to QNH below the transition level the pressure setting also starts flashing.
- Push the pressure setting knob on the EFIS control panel to set QNH barometric reference
- Rotate the pressure setting knob to set the local pressure setting
Hint - In the U.S. the transition altitude and transition level are 18,000ft but in Europe these values change depending on the weather and airport surroundings. Naturally you can find higher transition altitudes near mountainous terrain where it is important that aircraft know the correct height relative to mountains in the area.