en route flight advisory service 航路飞行咨询服务

air route flight 航迹飞行

en route flight watch 航路飞行观察哨

flight route 飞行路线

route-proving flight 试飞

high-altitude flight route 高空航线

cross-country flight route 长途飞行航线

route instrument flight rules altitude 最低航路仪器飞行高度

route familiarization flight 航路熟悉飞行