Reference: I’laam al-Mu’aasireen bi-Fataawa Ibn ‘Uthaymeen – Page 88
Question: With respect to the traveller, when do the rulings related to travel begin and end?
Response: With respect to him (the traveller), the rulings related to travel come into effect when he has left his town, and they end when he returns to his town. For example, if a person travels from ‘Unayzah, as soon as he has passed the buildings [of ‘Unayzah] and whatever is attached to them (outer buildings), then the rulings related to travel come into effect. And [likewise] based upon this, if he was travelling by plane, then he is to combine and shorten the prayers when he is at Qaseem Airport, because it is disconnected from the town (i.e. out of town).