OpenFlights Licence is favourable.
"Licensing and disclaimer
The OpenFlights Airport, Airline and Route Databases are made available under the Open Database License. Any rights in individual contents of the database are licensed under the Database Contents License.
Airport data derived OurAirports and DAFIF, as well as route data from Airline Route Mapper, is in the public domain. Airline data derived from Wikipedia may be subject to the GNU Free Documentation License. Whether these databases pass the threshold of originality and are thus copyrightable in the United States is an open question, and Contentshare does not assert the validity or lack thereof of such a claim.
This data is not suitable for navigation. OpenFlights does not assume any responsibility whatsoever for its accuracy, and consequently assumes no liability whatsoever for results obtained or loss or damage incurred as a result of application of the data. OpenFlights expressly disclaims all warranties, expressed or implied, including but not limited to implied warranties of merchantability and fitness for any particular purpose."
Download: airports.dat (~350 KB)
(a donation is suggested to help maintain the database)