Relations between tables

I have two tables (picture), AirportIn is a foreign key of AirportID, and AirportOut is also a foreign key of AirportID.

The problem is I can't make relations between these tables like this:

dataset.Relations.Add("AirportFlight", dataset.Tables["Airport"].Columns["AirportID"], dataset.Tables["Flight"].Columns["AirportIn"]);
dataset.Relations.Add("AirportFlight", dataset.Tables["Airport"].Columns["AirportID"], dataset.Tables["Flight"].Columns["AirportOut"]);

In runtime I get an error. How to solve the problem ?

Give the 2 relations unique names.