Claim: In 2019, the busiest domestic route at Adolfo Suárez, Madrid–Barajas International Airport, an international airport serving Madrid in Spain, is Catalonia Barcelona (served with three carriers), while the least busy domestic route is AsturiasOviedo,  (served with two carriers).
Evidence: Adolfo Suárez Madrid–Barajas Airport (Spanish: Aeropuerto Adolfo Suárez Madrid-Barajas [aeɾoˈpweɾto aˈðolfo ˈswaɾeθ maˈðɾið βaˈɾaxas) (IATA: MAD, ICAO: LEMD), commonly known as Madrid–Barajas Airport, is the main international airport serving Madrid in Spain. Busiest domestic routes at Adolfo Suárez, Madrid–Barajas International Airport (2019) Catalonia Barcelona 1 Air Europa, Iberia, Vueling AsturiasOviedo 10 Air Europa, Iberia