Do airlines have to plan their flights so that their flight route always follow an airway, or do they.........

Question

... also plan that they fly i.e. to VOR1, and the next waypoint would be VOR2, however, these 2 waypoints are not directly on one airway?

Answer 1

They do not have to follow airways.  They certainly may fly direct from VOR to VOR. IFR  Enroute Charts  depict some VOR-to-VOR routes that are not airways.

Answer 2

yes, they need to follow charted territory in case of the unthinkabe crash they will know the area a plane was flying in.

Answer 3

Airlines are not required to plan their routes along federal airways, however, many times they do.

The advantage of remaining on a federal airway is that you are guaranteed to have proper navigational and radio reception while on it.

Answer 4

Yes.

The information may be dated, but they fly radians off VOR and TACAN.

North/South and East/West flights fly at different altitudes to avoid contact.  Example:  odd thousand for N/S and even for E/W.

They do this, in part, to facilitate tracking. In part, for ease of flying (Automatic pilot)

Answer 5

When they file flight plans they’ll need to use navaids and/or airways just so there will be some reference on file as to what they’re planning to do. Once underway however, one can go direct anywhere if ATC approves it. With an FMC this is pretty easy. Without an FMC, they’ll just give you a heading and have you maintain it. In the middle of the night, I’ve been able to get a heading from Las Vegas to the initial fix on my JFK arrival, all without an FMC on board. No big deal.