Brazilian authorities have lifted a ban on flights from three major airports after fixing a failure in the air traffic communications system.
An equipment failure had prevented air traffic controllers from talking to pilots, throwing airports into chaos.
Take-offs were suspended in the capital Brasilia and in Belo Horizonte, while most were also cancelled at Sao Paulo's domestic airport.
International flights to and from Sao Paulo's other airport were unaffected.
Hundreds of flights were delayed and many passengers were forced to stay overnight at airports until the communications equipment was fixed early on Wednesday.
Landings were allowed at all three airports and the busy Sao Paulo-Rio de Janeiro shuttle was unaffected.
The director of Brazil's aviation agency, Milton Zuanazzi, said there had never been a collapse of communications like it before.
Flights throughout Brazil have already been disrupted for several months as air traffic controllers work to rule.
Following Brazil's worst air crash disaster in September, air traffic controllers have been refusing to handle more flights than international guidelines recommend.
They say they are overworked, underpaid and understaffed, putting safety at risk.
Authorities are still investigating whether air traffic controllers had a role in the 29 September mid-air collision over the Amazon jungle between a Gol airlines Boeing 737 passenger jet and a small executive jet.
All 154 people on board the Gol flight were killed.
A Brazilian court ruled on Tuesday that the two American pilots of the executive jet can leave Brazil.
Authorities had prevented them from leaving while the crash was being investigated.