John T wrote:

OK. What if the mechanic were not onboard the flight and it were only Mark
and the replacement crew (with nobody getting paid for their time)?

It still boils down to the fact that you can only share the expenses of a flight
that the group is making as an entity. The Feds have ruled that you cannot accept
compensation for transporting passengers unless you were going there anyway and
they're just along for the ride. You also can't advertise and take payment, and
that includes saying something to your friends like "Hey guys, I'm flying up to
Boston Saturday. Anybody wanna go along?" Half the people at Oshkosh probably
violate that one. It also includes offering to pilot a twin for free if you need
more twin time for a rating.

George Patterson
Battle, n; A method of untying with the teeth a political knot that would
not yield to the tongue.