Originally Posted by
PILOTGUY
No.
It is good for 24 calender months, unless you are employed continuously by a 121 carrier, then it does not expire. Took my ATP ride almost 6 years after the written test.
You do not have to be continually employed in order to use an expired ATP to upgrade at a 121 carrier. The FAR's say, verbatim, that you may use an expired written at a 121 carrier. No caveats about when or where you were employed prior to the upgrade.
I think the idea being that 121 employment and training covers the topics on the ATP written anyway.
It's possible that an individual airline might have a different policy, but I'm not sure why they would bother.