How are charter flights classified under international air law?

Under international air law, commercial air transport is categorized into scheduled air services and nonscheduled flights. Charter flights are generally classified as nonscheduled flights.1

Under the Chicago Convention on International Civil Aviation, contracting states agree to allow aircraft from other member states engaged in commercial nonscheduled flights to enter their territory without prior diplomatic permission. This includes the privilege to pick up and discharge passengers, cargo, and mail; however, in practice, this specific provision has become a dead letter.1

While charter flights fall mostly into the nonscheduled category, they do not do so invariably.1