George Kennedy's Best film
He's made lots of great ones, but I just saw what may be his best: The Human Factor (1975). He is the lead (not supporting) actor and his role is as a computer expert who's family is killed by terrorists. He singlehandedly tracks them down and...well I won't go further, but it's definitely a great ending! I also thought all the use of cutting edge (for the time) computer technology is of historical interest. The terrorists were those of the time: far-leftists allied with Arabs.
Anyway his other great ones where he is supporting actor are:
Flight of the Phoenix
Airport
Cool Hand Luke (for which he won the Oscar)
to name a few.