I think it is usually obvious who welcomes conversation and who does not. One time I was really happy about making a new friend was when we were on TACA next to the daughter of a TACA pilot. Her dad was piloting the leg of our trip from El Salvador to Guatamala City. She introduced us and he allowed my daughter (age 12) and me to ride the trip in the jump seats - got to see the volcanoes surrounding Guatamala City at night from a panorama window. Unforgettable.