The airline Eurowings is now enabling participants in the Miles&More frequent flyer program to partially pay for tickets with miles. The option is called "Cash & Miles" and requires that you have collected at least 3.000 miles.
Depending on how many miles you have in your Miles&More account, the fare can be reduced or you can get a free flight. The carrier also wants to appeal to infrequent flyers who have accumulated a few points, but these would not be enough for a free flight.