One black box from a crashed Lion Air jet has been recovered, which could be critical to establishing why the brand new plane fell out of the sky, the head of Indonesia’s National Transportation Safety Committee said on Thursday,.

“We found one of the black boxes,” Soerjanto Tjahjono told AFP.

“We don’t know yet whether it’s the FDR (flight data recorder) or CVR (cockpit voice recorder).”

The devices record information about the speed, altitude and direction of the plane as well as flight crew conversations.

They could be a key piece of evidence in determining why the Boeing-737 MAX 8, which went into service just a few months ago, plunged into the Java Sea off Indonesia’s northern coast on Monday, killing 189 people.

Images from the crash site showed two divers swim to a support vessel and place an orange-coloured device into a plastic tub, which was then carried onto the boat.

Despite their name, black boxes are typically bright orange.

Authorities picked up the box’s signals below the water’s surface on Wednesday, but were unable to get to the device immediately because of rough seas and strong currents.

AFP.