According to El Al’s Rav Hayut, even the duty free at Ben-Gurion International Airport which sold its chametz continued selling chametz during Pesach, transgressing the sale.
The rav points out however that El Al’s chametz was sold in strictest adherence to halacha, sold to a non-Jew by Rav Wosner, and it was under lock and key, stored away during yomtov in compliance with halacha. He recommends buying duty free items on board El Al flights to avoid problems
