Originally Posted by
Often1
[...] if connecting, will only need to pass through a TSA checkpoint if there is no airside physical route to your new departure gate.
Pretty much. For example, flew DUB-PHL. Went through DUB security, then DUB preclearence FIS security. Arrived in PHL, just walked to next gate.
Same goes for BOS if you're flying Aer Lingus or Westjet (provided you're flying jetBlue or Delta)
Air Canada, not so much... considering the gate area is the size of a cubicle and is isolated from the rest of the terminal. Thankfully, that's changing within the next 6-12 months.