Refers to a flight service or a plane trip, often used in contexts like booking or checking flight availability.
東京までの空の便を予約しました。
I booked a flight to Tokyo.
悪天候で空の便が欠航になった。
The flight was canceled due to bad weather.
Compound of 空 (そら, 'sky') + の (possessive particle) + 便 (びん, 'service, mail, flight'). Literally 'sky service'.