Originally Posted by steve64

At least at AA (I'd imagine all airlines are similar), the company's (IE: union contractual) duty limits would be reached before the FAA limits.
Crews may elect to overfly the union limits. Operations can't ask them to do it, the crew has to state they will operate the trip.
FAA limits can't be exceeded. Both sets of limits are multi-layered and convoluted so it isn't always easy to determine if/when they time-out.

AA liked to use the term "illegal crew" to describe any crewmember exceeding any limit. Oh the explanations that had to be given after passengers hear that phrase come out of the Gate Agt's walkie talkie. Particularly after the crew states they'll operate the trip anyhow.