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In Ethiopia Crash, Faulty Sensors on Boeing 737 Max Are Suspected In Ethiopia Crash, Faulty Sensors on Boeing 737 Max Are Suspected
(about 1 hour later)
A similar series of events involving faulty sensor data and an automated system suspected in bringing down a Boeing plane in Indonesia may have also caused the crash of the same type of jet in Ethiopia in March, according to people who have been briefed on the contents of the black box in Ethiopia. Black box data from a doomed Ethiopian Airlines flight suggests that the crash was caused by a faulty sensor that erroneously activated an automated system on the Boeing 737 Max, a series of similar events suspected in the Indonesian disaster involving the same jet last year.
Data from a vane-like device, called an angle-of-attack sensor, incorrectly activated the automatic, computer-controlled system, called MCAS, which pushed the nose of the plane down, eventually leading to a crash that killed all 157 people aboard. Data from a vane-like device, called the angle-of-attack sensor, incorrectly activated the computer-controlled system, according to three people who have been briefed on the contents of the black box in Ethiopia. The system, known as MCAS, is believed to have pushed the nose of the plane down, leading to an irrecoverable nose-dive that killed all 157 people aboard.
The black box, also called the flight data recorder, contains information on dozens of systems aboard the plane. The black boxes on both planes, Boeing’s latest generation of the 737, survived the crashes, allowing investigators to begin piecing together what caused the disasters. Both investigations are ongoing and no final determinations have been made. The black box, also called the flight data recorder, contains information on dozens of systems aboard the plane. The black boxes on both planes, Boeing’s latest generation of the 737, survived the crashes, allowing investigators to begin piecing together what caused the disasters. Both investigations are continuing and no final determinations have been made.
There are two angle-of-attack sensors on the Boeing 737 Max, one attached to the fuselage on the pilot’s side and another on the co-pilot’s side. Investigators in Indonesia, who have produced a preliminary report and released some of the information from the box, saw that one sensor produced a reading that was at least 20 degrees different from the other as the plane took off and began its ascent. The new connections between the two crashes adds to the pressure on Boeing, which faces scrutiny over the design and certification of the plane. Boeing played a major role in approving the 737 Max, as regulators delegated significant responsibility and oversight to the manufacturer.
The system was programmed to use data from only one of the sensors, which on that flight was malfunctioning. With the bad data, MCAS was activated, erroneously pushing the nose of the plane down. The pilots on the Indonesian flight tried repeatedly to override the system, but after about 12 minutes lost their battle and the plane crashed. The design and certification of the plane is the subject of multiple government inquiries. The Justice Department is investigating the plane’s development, while the Transportation Department’s inspector general is looking into the certification process. The inspector general has issued a subpoena to at least one former Boeing engineer for documents related to the 737 Max, according to a person familiar with the investigation.
MCAS was originally designed to activate based on data from a single angle-of-attack sensor, which measures the level of the jet’s nose relative to oncoming air. Air-safety experts, as well as former employees at Boeing and the supplier that made the sensor, have expressed concern that system had this single point of failure, a rarity in aviation.
Such sensors are highly reliable and have been used on passenger jets for years, but like any aircraft component, they can fail, the engineers said. Because the sensor is fallible, it is surprising that Boeing enabled it alone to activate a system that automatically pushes the aircraft toward the ground, said one former engineer who helped build the sensors at Rosemount Aerospace, a subsidiary of the industrial giant United Technologies based in Burnsville, Minn.
In a tacit acknowledgment that the initial design was flawed, Boeing unveiled a software update this week that would make the system rely on both sensors, instead of just one. If the two sensors disagree by a certain amount, MCAS will not engage.
Boeing said it could not comment on the black box findings until investigators release their official report, per international aviation agreements. A United Technologies spokeswoman did not immediately respond to requests for comment.
The sensors, which are effectively wind vanes on the jet’s nose, have malfunctioned in the past, for a variety of reasons, including bird strikes, according to the former engineers at Boeing and Rosemount. They have also been broken by jetways that attach to the plane for passengers to board and exit the plane.
The sensors can also malfunction if water pools around them and then freezes when the plane reaches a certain altitude, the engineers said. The sensors have built-in heaters to prevent freezing at such high altitudes, but they sometimes do not work quickly enough or can fail outright, the Rosemount engineer said.
Investigators in Indonesia, who have produced a preliminary report and released some of the information from the box, saw that one sensor produced a reading that was at least 20 degrees different from the other as the plane took off and began its ascent. With the bad data, MCAS was activated, erroneously pushing the nose of the plane down.
The pilots on the Indonesian flight tried repeatedly to override the system. But after about 12 minutes, they lost their battle and the plane crashed.
None of the people briefed said whether the black box data indicated how or whether the Ethiopian pilots tried to counteract the system. But the same bouncing, bobbing trajectory of the plane seen in the Indonesian flight as the pilots tried to save the plane is apparent in publicly available flight data for the Ethiopian plane.None of the people briefed said whether the black box data indicated how or whether the Ethiopian pilots tried to counteract the system. But the same bouncing, bobbing trajectory of the plane seen in the Indonesian flight as the pilots tried to save the plane is apparent in publicly available flight data for the Ethiopian plane.
Air traffic controllers in Ethiopia also said they saw the oscillating trajectory before the plane crashed. The pilot radioed back that he was having trouble controlling the aircraft, but did not give details on what systems were causing problems.Air traffic controllers in Ethiopia also said they saw the oscillating trajectory before the plane crashed. The pilot radioed back that he was having trouble controlling the aircraft, but did not give details on what systems were causing problems.