Boeing also said it will form a committee to review the company's policies and process for designing airplanes. It also noted that the accident is still being investigated.
The pilots then cranked a manual wheel in an attempt to stabilise the plane, the report said, but they eventually chose to restore power to the usual electric trim on their control yokes, likely because the manual attempt did not achieve the desired results.
Chicago-based Boeing, which is also the target of lawsuits over the October 29 Indonesia crash, has been working on a software fix and new training guidelines for the Max.
Family members of crash victims said they were unsettled by the report's findings.
The Ethiopian report clearly showed that MCAS - the Maneuvering Characteristics Augmentation System, a safety measure added to the new plane to prevent it from risky stalls - had activated multiple times.
In a statement, Boeing called the additional problem "relatively minor" but did not offer details of how the second issue affects the plane's flight-control system.
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Boeing's software-based MCAS system was added to the 737 MAX as a safeguard against stalling, but in both cases, investigators said a faulty sensor fed bad data into the system.
Ethiopian Airlines had on Thursday disclosed in its preliminary report, that the pilots of the ill-fated aircraft followed instructions that Boeing recommended and FAA approved emergency procedures to handle the most hard emergency situation created on the airplane.
Ethiopian Airlines has released a statement alongside the report which confirms that the crew complied fully with the correct operating procedures set for regaining control of the aircraft.
"Together, we'll do everything possible to earn and re-earn that trust and confidence from our customers and the flying public in the weeks and months ahead", Muilenberg added. The pilots followed the "emergency checklist" but could not take back control of the aircraft, according to the report. The plane made four nose dives before it crashed into the Java Sea.
In a statement, Boeing said that to make sure unintended activation of the MCAS system doesn't happen again, it is developing software and "associated comprehensive pilot training" for the Max.
The preliminary report, which stops short of determining the cause of the crash, chronicles the chaotic last moments aboard the flight before it crashed. As a result, three motions of the stabilizer trim were recorded.
Also the report does not address information about unreliable airspeed procedures which should be considered because they had erratic airspeed; and there is no information about the Auto-Throttle status - the FDR data appears to show the engines remained at a high power setting, said Mr Feith.