ADDIS ABABA, Ethiopia — A doomed Ethiopian Airlines jet suffered from faulty readings by a key sensor, and pilots followed Boeing’s recommended procedures when the plane started to nose dive but could not avoid crashing, according to a preliminary report released Thursday by the Ethiopian government.
The findings, including the faulty sensor data, drew the strongest link yet between the March 10 crash in Ethiopia and an October crash off the coast of Indonesia, which both involved Boeing 737 Max 8 jetliners. All 346 people on the two planes were killed.
Both planes had an automated system that pushed the nose down when sensors readings detected the danger of an aerodynamic stall, but it now appears that sensors malfunctioned on both planes.
Thursday’s report, based on flight data and cockpit voice recorders on the Ethiopian Airlines jetliner, showed that a faulty sensor on the plane touched off a series of events that caused the pilots to lose control of the plane. The report from Ethiopia’s Aircraft Accident Investigation Bureau said the sensor problems began about a minute after the plane was cleared for takeoff.
It said air speed and altitude values on the left side of the 737 Max conflicted with data from the right sensor, causing flight control problems. Eventually the Ethiopian Airlines pilots couldn’t keep the plane from crashing into the ground, killing all 157 people onboard.
The problems are similar to those reported on the Indonesian Lion Air flight that crashed last October. Investigators found that software on that plane took readings from the sensor and pointed the nose down. Thursday’s revelations raise questions about repeated assertions by Boeing and U.S. regulators that pilots could regain control in some emergencies by following steps that include turning off an anti-stall system designed specifically for the Max, known by its acronym, MCAS.
Investigators are looking into the role of MCAS, which under some circumstances can automatically lower the plane’s nose to prevent an aerodynamic stall. The Max has been grounded worldwide pending a software fix that Boeing is rolling out, which still needs to be approved by the U.S. Federal Aviation Administration and other regulators.
In a statement, Boeing acknowledged the faulty data from the sensor activated the MCAS system, which was similar to circumstances in the Lion Air crash.
The company said that to make sure unintended activation of the system doesn’t happen again, Boeing is developing software and “associated comprehensive pilot training” for the Max.
The software update, Boeing said in the statement, adds layers of protection and will stop erroneous data from activating the system.
Ethiopian investigators did not specifically mention the MCAS, but recommended that Boeing review “the aircraft flight control system related to the flight controllability.” They also recommended that aviation officials verify that issues have been adequately addressed before allowing the planes to fly again.
At a news conference, Minister of Transport Dagmawit Moges said the Ethiopian Airlines crew “performed all the procedures repeatedly provided by the manufacturer but was not able to control the aircraft.”
However, it wasn’t clear whether the Ethiopian pilots followed Boeing’s recommendations to the letter in dealing with the system repeatedly pointing the nose down.
The pilots initially followed Boeing’s emergency steps by disconnecting the MCAS system, but for an unknown reason, they turned the system back on, an official familiar with the crash investigation told The Associated Press on Wednesday. The official spoke on condition of anonymity because at the time, Ethiopian investigators had not released their preliminary report. Boeing’s procedures instruct pilots to leave the MCAS system disconnected and continue flying manually for the rest of the flight.
Ethiopian investigators did not address that issue at the news conference, saying only that the pilots had done what they were supposed to.
However, Moges told The New York Times after the press conference that the pilots turned MCAS on and off, but she couldn’t say how many times. That will be addressed in the final report, she said.
Boeing is the focus of investigations by the U.S. Justice Department, the Transportation Department’s inspector general, and congressional committees. Investigations are also looking at the role of the Federal Aviation Administration in the U.S., which certified the Max in 2017, declined to ground it after the first deadly crash in October. The agency was also reluctant to ground the planes after the Ethiopian Airlines crash and was among the last agencies to do so.
The FAA, which must certify the 737 Max is safe before it can go back into the air, said in a statement that the investigation is still in its early stages.
“As we learn more about the accident and findings become available, we will take appropriate action,” the agency said.
The statement did not say if the FAA would review the Max’s flight control system as recommended by Ethiopian investigators, and FAA spokesman Greg Martin would not comment beyond the statement. Boeing is working on improvements to the MCAS software that would make it less aggressive in pointing the nose down and easier for pilots to disable. The FAA has said it will review the software before allowing the Max to fly again.
The agency said Monday that it anticipates Boeing’s final software improvements for 737 Max airliners “in the coming weeks.”
