What is the definition of “Common Purpose”?
For example: I agree to fly someone from Cambridge to Glasgow and we fly there in my aircraft with him bearing half of the cost. Our common purpose is a desire to go to Glasgow. Is that enough? Or when we get there, do we then have to remain joined at the hip for the duration of our time there?
Supposing when we get there we each go to a separate and unrelated business meeting before flying back together that evening. Does that destroy our common purpose?
And what then about the return flight? When we fly back together, I want to go back to my home in Cambridge, and my passenger wants to go home to Kent. Am I allowed to drop him off at Biggin Hill when I have no absolute need to go there myself?
And after all that, suppose the “common purpose” is declared to be: “we both wanted to go for a flight”?
Personally, I think a better test of legitimacy would be: “Is the flight genuinely planned to happen anyway, whether someone shares the cost or not?”. I would also insist on the pilot paying at least an equal share.
That means that a pilot posting a flight on a site such as Wingly would have to specify a date, time and destination. The common purpose then would simply be a desire to get to that specific destination. That’s not to say that they can‘t cancel the flight if they don’t get a rider, or accommodate a reasonable request for an earlier or later departure time.
That would allow pilots to offer genuine cost share flights and, at least if properly policed by the flight share sites and the authorities, it should stop the “let me know where you want to go and when, and I’ll take you if you pay 99% of the costs” ads.