Originally Posted by IAN-UK

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But please note that use of 3-letter codes is not a requirement Indeed it's best to employ codes only when you are confident in their use, and confident that most people are familiar with them.

GDR is the code for the airport of Angra dos Reis. Angra is a small community in the extreme south of Rio de Janeiro state.

BA's current service to Buenos Aires is normally via Sao Paulo Guarulhos (GRU). It's a longish transit stop, and i think EZE-bound passengers are decanted airside: however you won't be required to enter Brasil, and I doubt that the Brasilian authorities have specific covid requirements for transit passengers. But if they do, or if some calamity requires a stop-over in Sao Paulo, I'm guessing you will be armed with PCR/vaccine certificates for Argentina.