An aeroplane is equipped with a Flight Director (with crosshair trend bars), heading 270° , in HDG mode (heading hold). A new heading, of 360° , is selected the vertical trend bar:
deviates to the right and will be centred as soon as you roll the aircraft to the bank angle calculated by the flight director.
deviates to the right and remains in that position until the aircraft has reached heading 360° .
disappears, the new heading selection has deactivated the HDG mode.
deviates to its right stop as long as the aeroplane is more than 10° off the new selected heading.