Terminal service units are used to calculate the total amount of terminal navigation charges paid by airspace users, mainly commercial airlines, for the air navigation services provided.
Terminal service units are a result of the mass of the aircraft raised to a specific exponent as defined below.
Terminal navigation charges, i.e. the price paid by airspace users, are equal to the total number of service units multiplied by the terminal unit rate.
Terminal service units are defined in the Annex V of the [[EC 1794/2006|charging scheme regulation]] (all references below refer to articles of this regulation):