The phrase "en route for" is correct and can be used in written English.
It means "on the way to" or "in the process of going to." Example: We are currently en route for the airport and should arrive in about an hour.
En route for London, Benouville was arrested in Algiers.
En route for holidays to his native Albania via Istanbul, he tells me that he initially planned to fly another European airline.
The frigate has now left, probably en route for Malta.
She was reportedly en route for an appearance in Independence Square.
Past Reims and en route for Troyes the gentle hills peter out.
Mrs Hoover changed trains at Philadelphia en route for Palo Alto, California, her home.
"Two days later, 50 of us were en route, for four days in the trains.
And pilgrims – yes, genuine pilgrims, straight outta Chaucer – en route for Santiago de Compostela.
Three spacecraft are en route for landings in December and January.
I see it as a hard climb, but he's en route for new adventures".
Late that evening they took a steamer en route for England, sailing early the next morning".
