Meaning of くうろ in Japanese

みなさま、空路の事故で到着が遅れる見通しです。
Ladies and Gentleman, due to an accident at the airport, our arrival will be delayed.

君の言っていることは机上の空論にすぎないよ。
What you are saying is nothing but building a castle in the air.

皆、空理空論ばかり言って、時間の無駄だよ、この会議は。
This meeting is a waste of time. Everybody is just talking in vague theoretical terms.

これらの青い線は、航空路をあらわす。
These blue lines correspond to airlines.