The Ethiopian Airlines plane that crashed last month nosedived several times before it hit the ground, a preliminary report has said.
Pilots “repeatedly” followed procedures recommended by Boeing before the crash, according to the first official report into the disaster.
Despite their efforts, pilots “were not able to control the aircraft”, Transport Minister Dagmawit Moges said.
Flight ET302 crashed after take-off from Addis Ababa, killing 157 people.
It was the second crash of a Boeing 737 Max aircraft in five months.
Last October, Lion Air flight JT 610 crashed into the sea near Indonesia killing all 189 people on board.
In a news conference in Addis Ababa, Ms Dagmawit said: “The crew performed all the procedures repeatedly [that were] provided by the manufacturer but were not able to control the aircraft.”
Her comments were based on a preliminary report into the crash, which has not been published yet, but could be released by the end of the week.
An investigation into the Lion Air flight suggested the system malfunctioned, and forced the plane’s nose down more than 20 times before it crashed into the sea.
The preliminary report from Indonesian investigators found that a faulty sensor on the aircraft wrongly triggered MCAS without the pilots’ knowledge.
Boeing has been working on an upgrade of the MCAS software since the Lion Air crash.
It has said the system can be disabled – allowing pilots to regain control if there appears to be a problem.
But the latest comments from Ethiopian officials suggest that pilots could not regain control, despite following procedures recommended by Boeing.
Now Boeing has issued guidance to pilots on how to manage MCAS.
It plans to install an extra warning system on all 737 Max aircraft, which was previously an optional safety feature.
It is also revising pilot training to provide “enhanced understanding of the 737 Max” flight system and crew procedures.
The planemaker says the upgrades are not an admission that MCAS caused the crashes.