Black Box data from a past Ethiopian Airlines flight indicates that the crash was caused by a faulty sensor that had mistakenly activated an automated Boeing 737 Max system, a series of similar events that occurred last year
Data from a wing-type device known as a pitch sensor has mis-activated the computer-controlled system, three people were informed about the contents of the black box in Ethiopia. The system, known as MCAS, is believed to have pushed the nose of the aircraft down, resulting in a non-recoverable dive that killed all 157 people on board.
The black box, also called flight data recorder, contains information about dozens of systems aboard the aircraft. The black boxes of both aircraft, Boeing's latest generation of the 737s, survived the crashes and allowed the investigators to pinpoint the causes of the catastrophes. Both investigations are ongoing and no final findings have yet been made.
The design and certification of the aircraft are the subject of multiple state investigations. The Ministry of Justice is investigating the development of the aircraft while the Inspector General of the Transport Department is investigating the certification process. The Inspector General has issued at least one former Boeing engineer a complaint for documents relating to the Max 737, according to a person familiar with the investigation.
MCAS was originally intended to be based on data from a single attack sensor that measures the level of the nozzle nose relative to the incoming air. Aviation security experts, as well as former Boeing employees and the supplier who made the sensor, expressed concern that the system had this single point of failure, a rarity in aviation.
Such sensors are extremely reliable and have been used for years by passenger jets, but like any aircraft component, they can fail, the engineers said. As the sensor is faulty, it is surprising that Boeing alone was able to activate a system that automatically pushes the aircraft to the ground, said a former engineer involved in the construction of the sensors at Rosemount Aerospace, a subsidiary of industrial giant United Technologies Based in Burnsville, Minn.
In a tacit affirmation that the original design was flawed, Boeing unveiled a software update this week that would require the system to rely on both sensors instead of just one. If the two sensors do not agree by a certain amount, MCAS will not turn on.
Boeing said he could not comment on the black box results until investigators publish their official report under international aviation agreements. A spokeswoman for United Technologies did not immediately respond to a request for comment.
The sensors, which are actually wind vents on the nozzle nose, have been bothered in the past for several reasons, including bird strikes, according to former engineers at Boeing and Rosemount. They were also broken by passenger board bridges, which are attached to the aircraft so that passengers can board and get off the plane.
The sensors may also malfunction when water accumulates around them and then freezes when the aircraft reaches a certain altitude, the engineers said. The sensors have built-in heaters to prevent freezing at such high altitudes, but sometimes they do not work fast enough or can fail, said the Rosemount engineer.
Investigators in Indonesia Submitting a Preliminary Report and Publishing Some of It The information from the box showed that one sensor produced a reading that was at least 20 degrees different from the other when the plane started and began its ascent , With the bad data, MCAS was activated and mistakenly pushed down the nose of the aircraft.
The pilots of the Indonesian flight repeatedly tried to override the system. But after about 12 minutes they lost their battle and the plane crashed.
None of the people said that the black box data indicated how or if the Ethiopian pilots had tried to counteract the system. The same bouncing, jiggling trajectory of the plane seen in Indonesian flight when the pilots attempted to rescue the plane is evident in publicly available flight data for the Ethiopian aircraft.
Air traffic controllers in Ethiopia said they saw the oscillating trajectory before the plane crashed. The pilot recalled that he had problems controlling the aircraft, but did not mention which systems were causing problems.