Per the Alaska contract, FA's can only be scheduled up to 10.5 hours in a duty period. They can, after having checked in, be rescheduled up to 12.5 hours in a duty period. Irregular operations (delays for most any reason) can require a FA to stay with their original trip indefinitely. That said, if a FA is at a domicile (any domicile) and they are projected to go past 14 hours they can opt to be removed from a trip and sent into rest. FAA rules state that FA's can't be originally scheduled longer than 14 hours but can extend indefinitely due to irregular operations. There are exceptions where a FA could be originally scheduled over 14 hours. No US airline currently does this that I know of, but it involves augmenting the crew with additional crew members. Hope that helps