Originally Posted by
Zaynab
I have no experience with pre-clearance airports, but logistics suggest AMS is a more logical choice than LHR. In AMS, security is done at the gate, with a "clean area" right after security. As such, it would be relatively easy to do pre-clearance at the gate, without the risk of screened passengers mingling with un-screened (potentially visa- or ESTA-less) passengers.
AMS is changing - the security check at each gate (in the non-Schengen area) will soon be a thing of the past.
US Pre-clearance could not be done under such a system. Once customers have passed through USCBP, they cannot then mingle freely or circulate in the airport - they only have access to the departure gates used for US flights. This requires a single facility and it involves its own security check. It would be impractical and unworkable to expect the USCBP officials to process passengers at whichever gate is assigned to the departing US flight. Instead, it requires dedicated gates which are accessible only to those who have passed through USCBP.