NOT IN lists are transformed into multiple predicates that use the <> operator.
<> predicates are not optimizable, but they are sargable. For example:
orig_airport NOT IN ('ABQ', 'AKL', 'DSM')
becomes
orig_airport <> 'ABQ' AND orig_airport <> 'AKL' AND orig_airport <> 'DSM'
In addition, large lists are sorted in ascending order for performance reasons.