Making a form with excluding fields to search for flights (iOS app)

I am currently facing a UX situation which I'm not sure how to solve.

I have a place on my app where I can search for flights inputting either the Airline, Departure and Destination airports, or the Flight Number.

One thought was to separate the airline, departure and destination fields from the Flight Number with an OR. I don't like too much this one, as it might be confusing if someone has filled more than one field.

Another could be a picker selecting which type of search (Dep/Dest airports or Flight Number).

What are your thoughts? What other ideas could be better?