I didn't check regarding international traffic law, but I don't see big troubles here in case an international company try to operates flights to Brazil, if the airport has capacity. To Sao Paulo Emirates got permission to fly without much trouble, actually the company has already permission to increase to two daily flights if they wish.

Domestic flights are the problem. The actual legislation restrict international capital participation up to 20% in National Companies. But, there are currently three projects of Law in the Senate (I'm just mentioning those originated in the Senate, the Lower Chamber can do as well, no time to research though...) to scrap this old protectionist legislation. I looked into the one proposed by the Senator Tiao Viana (Project # 259/2006). I choose this one because the guy is from PT (Labor Party) the folks that traditionally block any liberalization proposal in Brazil. To my surprise, the project is pretty good (proof that species can evolve; it doesn't differentiate anymore between Brazilian companies with or without national capital, i.e., any company located in Brazil (it's enough an office), is a Brazilian company, regardless of the ownership. Additionally, foreign companies can also operate internally. The bottom line, foreign companies can operate in Brazil.
Well, the project still have to be approved, but is really a good surprise to see this project coming from the government & Labor Party, as I said before, the folks that in the past object any economy liberalization. And please, don't come and say that the companies still will have to get flight permissions to fly from A to B, because if this is approved (my guess is yes), it will be a huge step forward.

For those who read Portuguese, here is a piece of the project justification:

"Seu caráter protecionista das empresas aéreas nacionais não mais se justifica, diante da demanda de transporte aéreo e da necessidade de ampliar a oferta desse vetor fundamental para o desenvolvimento do turismo e da economia nacional.(Bold added)

O Código não apenas veda a prestação de serviços aéreos por empresas estrangeiras, mas limita a participação do capital estrangeiro nas empresas brasileiras a 20%. Assim sendo, vigora um reserva de mercado absoluta, que impede o consumidor brasileiro de ter acesso a serviços de melhor qualidade e mais baratos.

Não há setor da economia nacional tão protegido contra a competição. Ao invés de fortalecer as empresas brasileiras, esse modelo, de duvidosa constitucionalidade, tornou-as acomodadas e ineficientes. Apesar de toda essa proteção, algumas das mais tradicionais companhias aéreas nacionais atravessam dificuldades financeiras e outras foram obrigadas a encerrar suas atividades.

Não menos importante é o benefício ao consumidor, que desfrutará de serviços melhores e mais baratos, em decorrência da ampliação da concorrência no setor.""

If you would like to check the project, just go to the Senate site and type the #:
Atividade Legislativa - Matérias Legislativas