Bearing south on excursion leaving runway (8)
I believe the answer is:
airstrip
'runway' is the definition.
(thesaurus)
'bearing south on excursion' is the wordplay.
'bearing' becomes 'air' (I've seen this before**).
'south' becomes 's' ('S' can be a synonym of 'south').
'on' says to put letters next to each other.
'excursion' becomes 'trip' (I've seen this before).
'air'+'s'+'trip'='AIRSTRIP'
'leaving' acts as a link.
(Other definitions for airstrip that I've seen before include "From which you might take off" , "(Unprepared) runway" , "Temporary runway" , "for those taking flight?" , "Land here" .)