Question

what is the meaning of the foreign expression in bold? when thunderstorms broke out in the region, air traffic controllers at the somerville airport scrambled to redirect flights already en route to somerville to other nearby airports. on the way exiting moving back about to depart

Explanation:

The phrase "en route" is a French expression. In English, it means "on the way". When flights are "en route to Somerville", it implies they are already in the process of traveling towards that destination. The other options: "exiting" (leaving a place), "moving back" (returning), and "about to depart" (just starting the journey) do not match the meaning of "en route".

Answer:

on the way