Portuguese government set up a no-fly zone above the Azores according to the U.S. Joint Intelligence Committee. Daily summary dated 18 March 1942

An item reported that the Portuguese government forbade aircraft to fly over the Azores and the territorial waters of that archipelago. Seaplanes which need to land or or near Horta were to allowed to that with clear weather flying on a maximum height of 200 metres.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 98 dated 18 March 1942.