Basically it's a clause in an air transport agreement, the model that Canada uses, that stipulates that our airlines should not be paying tax in more than one municipality. It's a similar clause to what we would use in any of our trade agreements.
Therefore, for our domestic carrier, whichever airline is flying those routes, if they are paying tax in one jurisdiction, either Canada or the other, the article ensures that they will not be paying taxation in both jurisdictions. It avoids double taxation. With some of our partners, they would use an agreement like this as an opportunity to collect tax revenue when it is already being paid. It ensure that airlines pay in only one jurisdiction.