Ethiopia's Civil Aviation Authority has released a preliminary report into the March 10 crash of an Ethiopian Airlines Boeing 737 MAX 8.
The aircraft crashed into a field 28 nautical miles (52 km, 32 miles) southeast of Addis Ababa's Bole Airport, six minutes into a flight to Nairobi. All 157 passengers and crew died in the accident.
The report highlights a number of issues on the doomed flight, including erroneous data from the Angle of Attack (AOA) sensors. Information from the left and right sensors, which are part of anti-stall equipment, differed dramatically at times during the flight.
Airspeed, altitude and pitch values also differed between sensors.
After the autopilot was disengaged, the nose was pushed down four times without any input from the pilot. The flight crew tried to correct the trim to counter the automatic input, but were ultimately unsuccessful.
Ethiopian Airlines said the preliminary report “clearly showed” that the pilots of the flight “have followed Boeing's recommended and FAA's approved emergency procedures to handle the most difficult emergency situation created on the airplane.
“Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the airplane from the persistence of nose diving. As the investigation continues with more detailed analysis, as usual we will continue with our full cooperation with the investigation team.”
The Ethiopian crash is the second involving Boeing's best selling 737 MAX range. A Lion Air 737 MAX 8 crashed off the Indonesian coast in October last year with the loss of 189 lives.
Boeing chief executive Dennis Muilenburg said “with the release of the preliminary report of the Ethiopian Airlines flight 302 accident investigation, it's apparent that in both flights the Maneuvering Characteristics Augmentation System, known as MCAS, activated in response to erroneous angle of attack information.
“The history of our industry shows most accidents are caused by a chain of events. This again is the case here, and we know we can break one of those chain links in these two accidents. As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment. It's our responsibility to eliminate this risk. We own it and we know how to do it.”
The preliminary report comes after the flight data and cockpit voice recorders were recovered and the data downloaded from the damaged devices by French accident investigators, the BEA.
The investigation is being led by Ethiopia's Aircraft Accident Investigation Bureau, with the Ethiopian Civil Aviation Authority, the US NTSB as representatives of the state of manufacture, France's BEA, and the European Aviation Safety Agency as technical advisers.
The final report could take up to a year to complete.