Indonesian investigators said on Wednesday a Lion Air Boeing 737 jet that plunged into the sea, killing 189 people onboard, was not airworthy on a flight the day before it crashed on Oct. 29.
The Oct. 28 flight from Bali to Jakarta had experienced similar technical issues to the doomed flight the next day from Jakarta to Pangkal Pinang, said Nurcahyo Utomo, head of Indonesia's national transport safety committee (KNKT).
The pilot of the Oct. 28 flight chose to press on to Jakarta after shutting down the plane's anti-stall system, Utomo said.
"This is the basis of our recommendation to Lion Air. In our view, the plane was not airworthy," he told a news conference in Jakarta.
Ahead of the release of its first report, the committee gave more details on the problems the pilots faced in controlling the plane before it crashed.
During the early morning flight, one of the pilots asked flight controllers to confirm the altitude and speed of the aircraft.
The pilot then reported that they were experiencing a "flight control problem," the statement said.
Last week, KNKT investigator Nurcahyo Utomo told parliament that the jet's Maneuvering Characteristics Augmentation System (MCAS) - an automated modification new to the model that crashed - activated and directed the jet's nose down to prevent a stall.
The jet's systems had detected it was in a stall due to a faulty indicator and gave the captain a warning through a "stick shaker" that vibrated the controls, he said.
Pilots flying the same plane a day earlier had experienced a similar problem until they used switches to shut off the system, KNKT said in its statement on Wednesday.
The agency recommended that Lion Air improve its safety culture to ensure that a pilot can make proper decisions to continue a flight.
The investigation into the crash is in its early stages and is hampered by the lack of evidence from the cockpit voice recorder, which remains lost on the seabed.
KNKT has not yet said what caused the crash and the recommendations are an indication of areas of focus, but not necessarily the ultimate cause.
On Wednesday, KNKT acknowledged actions to improve safety had been taken by Boeing, Lion Air, the U.S. Federal Aviation Administration (FAA) and Indonesia's Directorate General of Civil Aviation.
At Indonesia's request, Boeing issued an advisory about MCAS to airlines earlier this month. That was quickly followed by a U.S. Federal Aviation Administration directive making that mandatory.
— CNBC contributed to this report.