Bhutan has one international airport, Paro Airport, and two airlines, Druk Air (government-owned) and Bhutan Airlines (privately owned). Only these two airlines operate international flights to the country, as it takes specialized pilots and airplanes to land on a runway so short and so high in the mountains.
The schedules for Druk Air and Bhutan Airlines flights vary by season, but there are usually a number of flights each week from Kathmandu, New Delhi, Singapore and Bangkok. These flights are either direct or go through Dhaka, Kolkata or Bagdogra depending on the day of travel. There are on occasion flights from Guhawati and Ahmedabad. During the Thimphu tsechu (dance festival) in October and the Paro tsechu in April, there are more flights to the country. An easy option for you is to fly into Bangkok on Thai Airways or take a connecting flight on JAL, Korean, United, All Nippon, Air China, Asiana, Singapore, China, Eva and Cathay Pacific.
All landings and takeoffs in Paro are done by visual flight rules (VFR) in daylight hours. This means the pilot needs to see the runway before landing and the surrounding hills before takeoff. It also means that no flights are operated at night or in conditions of poor visibility, and cloudy days in the Paro valley will lead to long delays that can last for days.