A plane's black box records conversations of pilots, as well a monitors the mechanical systems and electronics of each flight.
"The captain said the problem was resolved and he made a decision to continue the trip to Jakarta".
Once retrieved, it could take up to three weeks to download their data and up to six months to analyse it, Soerjanto Tjahjono, the head of a national transport safety committee (KNKT), said.
Now experts have said a fault with a pitot pipe - which was found to have caused the Air France Flight 447 to crash into the Atlantic in 2009 - could have been responsible.
While victims' relatives are desperate to know what happened, the investigation of the first crash of a Boeing Co 737 MAX, which only went into service in August, is also the focus of scrutiny by the global aviation industry.
President Joko Widodo, visiting the search operation's headquarters at Jakarta's port, thanked rescue officials and the military involved and appealed for them to step up the search.
Radar showed that the aircraft climbed and descended erratically and that its speed increased dramatically.
The Boeing 737 MAX 8 crashed early on Monday just minutes after take-off from the Indonesian capital Jakarta. The chief of the police's medical unit, Arthur Tampi, said it has received dozens of body parts for identification and is awaiting results of DNA tests, expected to take 4-8 days.
According to Australian aircraft engineers, the 737's tech log had a record of an issue with "elevator feel and control" on the last flight the day before the tragedy.
"Today we will remove Lion's technical director from his duties to be replaced by someone else, as well as technical staff" who cleared the flight to depart, Budi Karya Sumadi told reporters.
Armed forces chief Hadi Tjahjanto said this afternoon a search and rescue effort has identified the possible location of the Boeing 737 MAX 8 in the Java Sea.
The pilot of flight JT610, which was bound for Pangkal Pinang in the Bangka-Belitung tin-mining region, had asked to return to base (RTB) shortly after takeoff.
There were 178 adult passengers, one child, two infants, two pilots and six cabin crew on board. But he acknowledged the plane's technical problems and said they were checked in Jakarta after it landed about 11:00pm, and the plane was deemed safe to fly the next morning.
The tragedy has raised questions about the safety record of a country whose airlines were for years judged too risky to fly over Europe.
Boeing reportedly suspended release of the 737 MAX just days out from its first commercial delivery previous year due to an engine issue, according to airline safety and product review site airlineratings.com. The ban was completely lifted in June.
Boeing and US National Transportation Safety Board officials have joined the Indonesian team in sifting through twisted metal plane parts and piles of passengers' torn clothing, shoes, wallets and phones. Local airline traffic more than tripled between 2005 and 2017 to 97 million people, according to the CAPA Center for Aviation, and is dominated by flag carrier PT Garuda Indonesia and Lion Air Group.