The almost brand new Boeing 737 MAX crashed into the Java Sea after leaving Jakarta on October 29. The jet, which is the latest version of the 737, had problems on its previous flight the day before.
At a press conference, investigators said maintenance procedures were not followed correctly.
"In our opinion, the plane was no longer airworthy and it should not have continued," the BBC quoted Nurcahyo Utomo, aviation head at Indonesia’s National Transport Safety Committee.
Data shows the aircraft experienced problems with airspeed readings and altitude. Its anti-stall system forced the nose of the aircraft down 26 times in 10 minutes before it hit the sea at 400mph.