AtD translation: flying bridge

[Mike Jing]

P775.20-24   And they were on the move once again, aboard a river steamer
down the Angara, as it was known at this end—its name would change farther
along to Upper Tunguska—past the city, beneath the great flying bridge,
borne by the current flowing out of Lake Baikal, north into the beating
heart of shamanic Asia.

What is the "flying bridge" here exactly?