Authorities sifting through the crash site where Ethiopian Airlines Flight 302 plunged from the sky — killing all 157 people on board — said they recovered the aircraft’s so-called “black box” Monday, a critical discovery in the search for what caused the disaster.

Ethiopian Airlines announced on Twitter the Digital Flight Data Recorder and Cockpit Voice Recorder had both been recovered from the crash site at Bishoftu, or Debre Zeit, located some 31 miles south of where the plane took off from the capital of Addis Ababa.