There's no train connection with Managua Airport.
Car and bus
Managua International Airport is situated 12 kilometers north of the city center. In a rental car you can cover this distance in 15 minutes via the Carretera Norte C1 or the Carretera A Sabana Grande.
City bus 266 connects the airport with Managua City. Buses leave every quarter.
Car rental Managua Airport
You can find desks of car rental companies in the Arrivals Hall. Eight rental companies are present at Managua International Airport: Alamo, Budget, Dollar, Hertz, National, Payless, Thrifty and Toyota Rent-a-Car.
The taxis outside the Arrivals Hall all have a meter. For destinations outside the city you need to agree on a price with the driver upfront. The airport taxis are quite expensive; it's a lot cheaper to walk to the main road and stop a taxi there.
There's a small parking lot outside the main building. You pay 20 cordobas for the first hour, and then 10 cordobas per half hour.