Until hauteboy's great tool is back online, if you are stuck with a flight you -know- exists, but the validator rejects it, here's a workaround.

Say you want to check a RTW that includes DFW-ANC. Now, because DFW-ANC is a seasonal flight, and the tool is currently "stuck" at a time of the year when that flight was not available, you too are stuck, until the tool is finally updated. You can substitute DFW-ANC with a dummy segment, but that is not very satisfactory.

So, here's what you do, with apologies to the software author for taking the liberty of semi-hacking his work:

0. Make a backup copy of flights.js
1. Open flights.js with a text editor (Notepad will do).
2. Find a really weird city pair, one you know you will never ever use.
3. *Carefully* replace the original city pair with the new city pair.
4. Repeat steps 2 and 3 for each new flight you want to introduce.

Save the file and run the tool. Presto! you have now *created* new flights and can go on using the tool.