ADDIS ABABA, Ethiopia — Just two minutes after takeoff, the captain of the doomed Ethiopian Airlines Flight 302 said the plane was having problems. Pilots then began having trouble controlling the aircraft.
In the plane’s short and fatal flight, pilots followed safety procedures recommended by Boeing, performing actions on the emergency checklist, including cutting off electricity to an automatic system that was pushing the nose down. But they were still unable to prevent the jet from crashing, according to an initial report by Ethiopian investigators.
About six minutes after takeoff, the plane went into a fatal dive that killed all 157 people on board.
The report, released Thursday, laid out a timeline of the flight based on analysis from 18 Ethiopian and international investigators and information from the jet’s flight data recorder and cockpit voice recorder. The investigators’ initial report was released several hours after a news conference held by Ethiopia’s minister of transportation.
The data showed that shortly after liftoff, a crucial sensor that measures the angle that the plane is moving through the air, began fluctuating wildly on the pilot’s side, falsely indicating that the plane was close to stalling. The sensor, one of two angle of attack sensors on each side of the plane’s nose, began giving readings nearly 60 degrees different from that of its counterpart.
About a minute and a half after takeoff, after the pilots had performed routine tasks like retracting flaps on the wings, the false reading appears to have set off an automated system known as MCAS, the black box data shows. MCAS is intended to prevent a stall and began rapidly pushing the nose of the craft down.
Left sensor angle
Right sensor angle
Left sensor angle
Right sensor angle
The pilots countered that by pushing electrical switches on their control wheels that adjusted the angle of stabilizers on the tail of the plane, which had been moved by MCAS. About five seconds after the pilots tried the right the plane, MCAS again engaged, moving the stabilizers to a dangerous angle in another nose-down action.
The pilots pushed the electrical switches again. Then, the report says, they followed the emergency checklist and disabled the entire stabilizer electrical system using the so-called stabilizer trim cutout.
“The first officer called out ‘stab trim cutout’ two times,” the report says. “Captain agreed and first officer confirmed stab trim cutout.”
Although that move disabled MCAS, it also forced the crew to control the stabilizers manually with wheels at their feet — a physically difficult task on a plane moving at high speed. A little under four minutes after takeoff, the first officer said the manual method “is not working.”
Soon after, the black box data indicates, the crew turned electricity back on and tried two more times to move the stabilizers by hitting the switches. But once they turned the electricity back on, MCAS engaged again, putting the plane into a dive from which it would not recover.
The crash of Ethiopian Airlines Flight 302 on March 10 followed the unrecoverable nose-dive almost five months earlier of another jet of the same model, a Boeing 737 Max 8, in Indonesia. Indonesian investigators have implicated MCAS in that disaster, in which the plane’s computer system appeared to override pilot directions based on faulty data.
“These guys are executing the checklist,” Dennis Tajer, a spokesman for the American Airlines pilot union, said of the Ethiopian pilots after reviewing the report. “They were identifying the problem and taking swift action.”
The initial findings are likely to heighten scrutiny of the Max, Boeing’s newest and top-selling generation of jets. Since the Ethiopian Airlines crash, airlines worldwide have grounded their Max fleets, amid concerns over the apparent propensity of MCAS to malfunction when fed erroneous data.
Ethiopian authorities portrayed the pilots of the plane in a positive light. Dagmawit Moges, Ethiopia’s minister of transportation, said that the flight crew repeatedly followed procedures recommended by the plane’s manufacturer “but was not able to control the aircraft.”
Both 737 Max 8 jets crashed at high speed minutes after takeoff in clear weather, following roller-coaster trajectories that hinted at desperate struggles by pilots to control planes seemingly immune to their interventions.
In a statement on Thursday, Boeing’s chief executive, Dennis A. Muilenburg, said that the company was “confident in the fundamental safety of the 737 Max.” Boeing has said it plans to release a software update to MCAS soon, along with increased pilot training for the 737 Max planes.
“This update, along with the associated training and additional educational materials that pilots want in the wake of these accidents, will eliminate the possibility of unintended MCAS activation and prevent an MCAS-related accident from ever happening again,” Mr. Muilenburg said.
After the report from Ethiopia was released, Boeing said it was working “to ensure unintended MCAS activation will not occur again.”
“Boeing has developed and is planning to release a software update to MCAS and an associated comprehensive pilot training and supplementary education program for the 737 Max,” the company said in a statement.
Investigations into both crashes are continuing. A final report on the Lion Air accident is expected in August, at the earliest. Ethiopian officials said on Thursday that their final findings could take a year to be released.
Indonesian investigators have focused on whether the anti-stall system was activated by incorrect data on the plane’s angle of attack, essentially a measure of an aircraft’s likelihood of stalling.
After the Lion Air crash last October, pilots and airlines complained that they had not been adequately briefed on MCAS by Boeing. The Max manual had no specific mention of how to correct a malfunctioning MCAS. Some pilots reported that they had not even known of the software’s existence.
In creating the Max jet, Boeing added bigger engines to the 737, which gave the airplane the fuel efficiency it needed to compete with a new model from its rival, Airbus. But the change also altered the jet’s aerodynamics and the larger engines had a tendency to push the airplane’s nose up in certain flight conditions.
To compensate, Boeing engineers created MCAS, which was meant to make the Max behave more like older versions of the 737. To receive certification to fly the Max, some pilots with prior 737 experience had to complete only a couple hours of online training.
Boeing has said that existing procedures were sufficient to address a MCAS malfunction, but early data suggests that pilots on the doomed flights may not have known how to disengage the system, or may have done so too late to save their flights.
Most airplane systems are built with backup redundancies to prevent a single data malfunction from altering a plane’s course, but MCAS is activated by data from just one angle-of-attack sensor, not two.
The Federal Aviation Administration released a statement saying it was still working with Ethiopian officials to investigate the crash. “As we learn more about the accident and findings become available, we will take appropriate action,” the F.A.A. said.
In the news conference, Ms. Moges, the transport minister, cautioned against holding any party responsible for the plane’s fatal plunge.
“The major objective of this investigation is to make sure that there is safety in the aviation sector,” she said. “It is not to blame someone.”