The crash of Ethiopian Airlines Flight 302 on March 10, 2019, shortly after takeoff from Addis Ababa, resulted in the loss of all 157 people on board. This tragic event brought to light critical questions about the emergency procedures and the aircraft's control systems, particularly the Maneuvering Characteristics Augmentation System (MCAS). This article delves into the events leading up to the crash, the actions taken by the pilots, and the subsequent investigations and recommendations.
Ethiopian Airlines Boeing 737 MAX 8
The Crash and Initial Findings
Ethiopian Airlines Flight 302 was a scheduled international passenger flight from Bole International Airport in Addis Ababa, Ethiopia, to Jomo Kenyatta International Airport in Nairobi, Kenya. The aircraft was a new Boeing 737 MAX 8, delivered to Ethiopian Airlines on November 15, 2018. On 10 March 2019, the Boeing 737 MAX 8 aircraft which operated the flight crashed near the town of Bishoftu six minutes after takeoff.
The Ethiopian government reported that data from the plane’s recorders showed "repetitive uncommanded aircraft nose-down conditions" and suggested that Boeing should review its aircraft control system. According to the country’s transport minister, Dagmawit Moges, the crew performed all procedures repeatedly provided by the manufacturer but was not able to control the aircraft.
The pilots of the Ethiopian Airlines 737 Max that crashed last month killing 157 people correctly followed Boeing’s emergency instructions but were still unable to stop the plane’s nose repeatedly pointing down, investigators said. In the final seconds before the crash, pilots tried desperately to right the plane by switching its anti-stall software on and off but to no avail. The jet hit an airspeed of 500 knots (575mph), well above its operational limits, before cockpit data recordings stopped.
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Ethiopian Airlines said the report clearly showed that the pilots had followed procedures. "Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the plane from the persistence of nosediving," it said.
The initial findings intensified pressure on Boeing to explain and resolve the issues with its Max jets, the company’s newest airplanes, which have been grounded worldwide following two fatal crashes in five months. It was the second crash of a 737 Max after the Lion Air disaster in Indonesia in October, which killed 189 people.
Emergencies in the Boeing 737 MAX 8! | Multi-Crew Coordination Course (MCC)
Detailed Flight Analysis
Forty-four seconds after takeoff, the angle of attack (AoA) sensor on the left side of the aircraft sustained damage, possibly from a bird strike. This damage caused the sensor to send faulty readings, leading the Maneuvering Characteristics Augmentation System (MCAS) to falsely detect an imminent stall. In response, MCAS repeatedly commanded the horizontal stabilizer to push the aircraft's nose downward.
Approximately one minute into the flight, the first officer retracted the flaps, following the captain's instructions. Within 10 seconds of this action, the autopilot disengaged, and the aircraft started to descend. By the second minute, the MCAS had angled the horizontal stabilizer sharply downward, pitching the aircraft into a dive. The first officer, correctly identifying that they were experiencing a runaway MCAS activation, called out "Stab trim cut-out!"
The pilots toggled switches to disable the aircraft's electrical trim tab system, which also deactivated the MCAS software. Without the electric trim system, the other possible way to move the stabilizer is by cranking the trim wheel by hand, but because the stabilizer was located opposite to the elevator, strong aerodynamic forces were acting on it due to the pilots' inadequate thrust management. At the plane's high speed, there was further pressure on the stabilizer.
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Three minutes into the flight, with the aircraft continuing to lose altitude and accelerating beyond its safety limits, the captain instructed the first officer to request permission from air traffic control to return to the airport. Permission was granted, and the air traffic controllers diverted other approaching flights. Following instructions from air traffic control, they turned the aircraft to the east, and it rolled to the right.
About five minutes into the flight, having struggled to keep the plane's nose from diving further by manually pulling the yoke, the captain turned the electrical trim tab system back on in the hope that it would allow him to put the stabilizer back into neutral trim. However, in turning the trim system back on, he also reactivated the MCAS software, which reactivated nine seconds later and pushed the nose further down.
Boeing's Response and Recommendations
After the Lion Air crash, Boeing issued instructions to pilots on how to override the MCAS system, but the Ethiopian crash report suggests they may not have worked. On Thursday Boeing announced that new software would ensure that pilots will always have the authority to override the system if it is activated by faulty sensor data.
Boeing says it has developed an MCAS software update to provide additional layers of protection from the system activating due to erroneous data. The update will also limit how powerfully the flight system acts, and was put through hundreds of analysis while its chief executive Dennis Muilenburg joined the test flight yesterday, the company said. It has to be approved by the FAA, however, and it is unclear when it would be deployed by airlines.
Kevin McAllister, Boeing Commercial Airplanes president and chief executive, stated, "Understanding the circumstances that contributed to this accident is critical to ensuring safe flight. We will carefully review the AIB’s preliminary report, and will take any and all additional steps necessary to enhance the safety of our aircraft."
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Timeline of the Boeing 737 Max Crisis
The following table summarizes key events in the Boeing 737 Max crisis:
| Date | Event |
|---|---|
| May 22, 2017 | Boeing 737 Max enters commercial service |
| October 29, 2018 | Lion Air crash |
| November 7, 2018 | Boeing's new advice |
| March 10, 2019 | Ethiopia Airlines crash: Flight ET302 crashes about six minutes after taking off from Addis Ababa, killing all 157 people onboard. |
| March 13, 2019 | Boeing grounds fleet: The EU, Canada and the US all ground the Boeing 737 Max. |
| April 4, 2019 | Interim report findings: The interim report into the Ethiopian Airlines crash finds that the pilots correctly followed Boeing’s emergency instructions, but were still unable to stop the plane’s nose repeatedly pointing down. |
| June 27, 2019 | A new potential risk: Airlines extend their ban on using the Boeing 737 Max after the US aviation regulator said it had identified a new potential risk with the plane. |
| July 10, 2019 | Airbus soars: Airbus seems set to overtake Boeing as the world's biggest planemaker. |
| October 30, 2019 | Sensor concerns ignored: Lawmakers were shown internal records revealing that three years before the crashes an employee had expressed concern that an anti-stall flight system could be triggered by a single sensor. |
| January 10, 2020 | The crisis deepens with the release of hundreds of internal messages between employees working on the 737 Max aircraft, which boasted of deceiving safety regulators and said the plane had been “designed by clowns”. |
| February 19, 2020 | Boeing orders inspections of its entire fleet of grounded 737 Max planes after it found foreign object debris in the fuel tanks of some of the mothballed planes. |
Pilot Training and Procedures
As the potential problems with the automated system became better known, the question of whether pilots were well-versed with how to deal with the plane’s MCAS system has also come into focus. Many pilots in the US qualified to fly the earlier version of the 737, on which the Max is based, only received training amounting to “an iPad lesson for an hour,” which did not cover the anti-stall system.
The procedure Boeing recommended to airlines after the Lion Air crash, which was repeated in an airworthiness directive issued by the FAA, includes a line near the bottom that “higher control forces may be needed to overcome any stabilizer nose-down” position.
MCAS Schematic
Ongoing Investigations and Analysis
While air investigation reports do not apportion blame, the Ethiopian inquiry has again highlighted the 737 Max control system. Indonesian investigations into the Lion Air crash have focused on Boeing’s anti-stall system, Mcas, new on the Max model of 737 aircraft.
The Ethiopian Civil Aviation Authority (ECAA) released an interim report on the crash on March 9, 2020. This report stated that the left and right angle of attack (AOA) values deviated by 59°. The AOA disagree message did not appear. The left minimum operating speed and left stick shaker speed was computed to be greater than the maximum operating speed without any invalidity detection. The pitch Flight Director bars disappeared then reappeared with left and right displaying different guidance. The left stick shaker activated. The nose-down trim (MCAS) triggered four times. The right over-speed clacker activated. On the third MCAS trigger there was no corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches being in the "cutout" position at that moment. The MCAS design relied on single AOA sensor inputs making it vulnerable to undesired activation.
The US team concurs with the EAIB's investigation of the MCAS and related systems and the roles that they played in the accident. However, many operational and human performance issues present in this accident were not fully developed as part of the EAIB investigation. These issues include flight crew performance, crew resource management (CRM), task management, and human-machine interface.
