According to this
BBC article, both aeroplanes were equipped with TCAS and the collision was "inexplicable". Excerpt below.
The Estado news agency reported that the Legacy was piloted by a US citizen who had taken off from the Sao Jose dos Campos airport near Sao Paulo.
Ramon Bueno, an aviation official in Sao Paulo, told Estado that the mid-air collision was "inexplicable."
He said that the two planes were "very modern and have anti-collision systems, which sound an alarm to alert the plane to any obstacle".