Most airplanes using airports in that area, are generally cargo flights that cannot do non-stop flights, because of heavy payloads, from South America to Europe, or back. At the present time, Recife gets the brunt of that traffic, with Fortaleza as the filed alternate airport.
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Most passenger flights from Europe to South America do overfly that area, and use Recife and Sal (Cape Verde) as their ETP oceanic alternates for ETOPs computations in the case of 2-engine aircraft, so the use of Natal would be limited in considering that type of traffic.
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One thing however, is the tourist industry. While NE Brazil ("Nordeste") as they say in that country, was a economically depressed area, the afflux (I call it an invasion) of tourists from Europe to the beach resorts, might change the image of the traffic, and Natal would be a good addition. Tourist air traffic to Fernando de Noronha islands, a little tourist paradise just off the coast from Natal would also be a bonus, as connection point for smaller aircraft.
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Brazil, now, finally a nation with outstanding economic future should never be discounted for investments, and strong ties exist between the EU and Brazil.
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Happy contrails