During the Crysis 3 Mission 2: Welcome to the Jungle, you can collect two blackboxes.
Crysis 3 Blackbox no.
Once you reach the subway and defeat all enemies, jump over a huge gap in order to meet with Psycho. After the jump, you will enter the room full of dead soldiers. The blackbox is next to the dead soldier behind Psycho (screenshot no. 2).
Crysis 3 Blackbox no. 2
In order to proceed you need to smash a red door and go up the stairs. Once you reach the North railyard area, drop down one level, and you will find the second blackbox in the upper right corner of the map. The blackbox is next to a dead soldier and ammo crate.