The VFR sectionals show a number of airways/routes marked in red. Here are several near KMTH, you can see B-646 extending east of the NDB:
There are others in Alaska that are lettered A, R or G, e.g. A-7 runs between the CMQ and MNL NDBs.
What are these airways or routes and how are they different from Victor airways?
These are Red Federal Airways, and can be found in Order 7400.9
Red airways are one of a 1950s-ish system of airways: Red, Blue, Green, Amber, which are designated by an NDB (rather than a VOR or VORTAC for a V or J route).
Green and Red airways go east/west, and Blue and Amber routes go north/south.
These routes were prioritized: GARB, with Green routes having the highest priority.
