Fua'amotu International Airport (TBU), 21 km southeast of Nuku'alofa, is closed on Sunday. Domestic flights use the old terminal, beyond an army camp about two kilometers by road around from the new international terminal.
A special airport bus meets most flights but if there are two or more of you, the taxi fare to town is just as good. Be sure to check the fare before getting into the taxi, and don't let the driver steer you to some hotel you never intended to stay at just so he can collect a commission. Often they will tell you the hotel you requested is closed with the aim of tricking you into going where they want. Know exactly where you want to go and how before you step out of the terminal. Hope that your flight doesn't arrive in Tonga late at night, as the taxis demand fifty percent more then.
Some accommodations provide free transfers from the airport if they know you're coming (ask) but charge a fee to drive you back there. Several companies have car rental offices at the airport. Airport-bound, you can book a bus from the main hotels directly to the terminal. If you're on the lowest of budgets you could also take the infrequent Fua'amotu bus right to the airport access road, or any Mu'a bus to the crossroads at Malapo, then hitch the last six km.
The Tonga Visitors Bureau counter and bank exchange office are to the right as you come out of arrivals. The bank at the airport changes traveler's checks at a rate similar to the banks in town, less a commission. Western Union offers a similar exchange rate without commission. There's also an ATM. A snack bar and duty-free shop are in the departure lounge.
Check in early as international flights are often overbooked and this airport is mildly chaotic. The T$25 departure tax on international flights is included in your plane ticket.