OpenFlights

About

FAQ says:

In a nutshell, it's a tool that lets you map your flights around the world, search and filter them in all sorts of interesting ways, calculate statistics automatically, and share the resulting maps with friends and the world. You can also check airport route maps for nearly every airport in the world and find out what airlines fly where.

Format

More on data format at:

• http://openflights.org/data.html

Openness

As of October 2009, data is available under the Open Database License (ODbL):

• http://openflights.org/blog/2009/10/13/comprehensive-airline-route-data-released/