Polar express: How airlines are plotting a new route to Asia

A Russian airspace blockade meant quickly diverting some Europe to Asia flights over the North Pole. Here's how an airline creates a new route over the top of the world.

(CNN) — The closure of Russian airspace to some international carriers, including many in Europe, has forced airlines to seek alternate routes. For some flights, such as those linking Europe and Southeast Asia, that's especially problematic since Russia, the world's largest country, stands directly in between.

The problem is best illustrated by Finnair's flight from Helsinki to Tokyo. Before the invasion of Ukraine, planes from Finland's national carrier would take off and quickly veer into the airspace of neighboring Russia, crossing it for over 3,000 miles.

They would then enter China near its northern border with Mongolia, fly in its airspace for about 1,000 miles, before entering Russia again just north of Vladivostok.