"From what we know, there are nine things that contributed to this accident," Indonesian air accident investigator Nurcahyo Utomo told reporters at a news conference.
"If one of the nine hadn't occurred, maybe the accident wouldn't have occurred."
The 353-page report found the jet should have been grounded before departing on the fatal flight because of an earlier cockpit issue.
However, because the issue was not recorded properly the plane was allowed to take off without the fault being fixed, it said.
Further, a crucial sensor - which had been bought from a repair shop in Florida - had not been properly tested, the report found. On Friday, the US aviation regulator revoked the company's certification.
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Further, the report found that the first officer, who had performed poorly in training, struggled to run through a list of procedures that he should have had memorised.
He was flying the plane just before it entered into the fatal dive, but the report said the captain had not briefed him properly when he handed over the controls as they struggled to keep the plane in the air.
The report also found that 31 pages were missing from the plane's maintenance log.