Due to the capacity constraint of Haneda Airport, airlines in Japan have to rely on large-size aircrafts to increase capacity for transporting increasing volume passenger in domestic aviation. Consequently the average aircraft-size has been unusually large in Japanese domestic market in comparison with the other western countries. This means that level of service in terms of the flight frequency is low in many air routes in Japan. In this study, first, we broadly compare the flight frequency and aircraft size among major countries. Second, in order to get an idea on the potential flight frequency, we analyze the flight frequency in US and Japan from taking into account the characteristics of each air route such as passenger demand, route distance and number of airline entries. The study results, though based on simple quantitative analysis, provide valuable insights for policy makers concerning future strategies in expanding capacity of Haneda Airport.