Brien K. Meehan wrote:
Is it customary for passengers to tip their charter or sightseeing
pilot?

Customary, no. Appreciated, yes. I don't know why, exactly, except it
makes you feel that you are being recognized for a good job. The money
was nothing to me; after all, I am a retired successful businessman who
already has everything he needs. It was just the sign of appreciation
that I liked.

I made a practice of splitting my tips 50/50 with the line guys. This
did two things: 1) it made sure that my passengers always had a red
carpet and primo parking spot; and 2) the treatment encouraged my
passengers to give me more tips.