航线 (hángxiàn) is a noun meaning "route" or "shipping/air lane." It refers to a regular path followed by ships or aircraft, and is commonly used in transportation and travel contexts when discussing flight paths or shipping routes.
这条航线每天有三个班次。
Zhè tiáo hángxiàn měi tiān yǒu sān gè bāncì.
There are three flights per day on this route.
航空公司新开了一条从北京到伦敦的航线。
Hángkōng gōngsī xīn kāi le yī tiáo cóng Běijīng dào Lúndūn de hángxiàn.
The airline has opened a new route from Beijing to London.
这条航线的票价最近降了不少。
Zhè tiáo hángxiàn de piàojià zuìjìn jiàng le bù shǎo.
The ticket price for this route has dropped quite a bit recently.