In case anyone reads this in the future, here’s what I did.
As posted previously there’s no (currently as far as I can see) no native autocomplete for AirportInfo (unlike say UA* for Search endpoint). So I did a call to AllAirports and cached locally (JSON parsing in Swift 4 is beautiful) then all you need is a call to AirportInfo (or NearbyAirport in v3) with an airportCode (or airport_code) that you obtain from the user in say an UISearchController (assuming iOS with Swift 4). Just be mindful that a separate call to AirportInfo will happen for each filtered object in UISearchResultsUpdating so you may want to limit that to the top 3 (say).
Like I said, this approach is already documented previously in this forum but thought I’d write my experience with Swift and iOS.