What is required for an airline to operate in another country?

For an airline to operate in another country, a bilateral air transport agreement is essential. This agreement is a formal arrangement between two countries that establishes the terms under which airlines from each country can operate flights to and from each other's territories. It defines key aspects like the rights to operate, routes, and the frequency of flights, ensuring that both nations benefit from the arrangement.

In the context of international aviation law, these agreements are crucial because they provide the legal framework for cross-border airline operations, ensuring compliance with each country's regulations and promoting fair competition. Without such an agreement, airlines cannot legally perform international flights between the two countries, rendering them unable to expand their services across borders efficiently.

The other options, while important in their own contexts, do not directly pertain to the fundamental legal requirement for operating international flights. Local weather conditions can influence operational decisions but are not a regulatory prerequisite. Membership in international aviation organizations may offer benefits and support but is not required for operating in another country. Investment in local airports could enhance services and operations but is not a necessity for obtaining the authorization to fly internationally.