Originally Posted by
ashill
Huh? Isn’t the main point of preclearance to serve airports without Customs (the prime examples being LGA and DCA)?
No, it's not. Pre-Clearance is just that. PRE clearance.
The flight is still required to land at an airport with full AoE status so that if USCBP choose, they can re-clear the flight.
Alaska learned this the hard way when they scheduled YVR-SNA before SNA was an AoE, and the flight had to sit on the ground for hours for US Customs to arrive only to say "OK". Alaska cancelled the route after one day.