Andorra still doesn’t have its own international airport. Andorra-la Seu d’Urgell airport is still in the process to get a license for becoming an international airport. Authorities expect that to happen in May 2019.
The closest airport you can fly to is the La Seu d'Urgell airport in Spain, which is located about 10km to the south of the Spanish-Andorran border. There are various transports from this airport to Andorra – you can rent a car, use taxi services or check out the bus timelines.