Boeing Built Deadly Assumptions Into 737 Max, Blind to a Late Design Change - The New York Times
A year before the plane was finished, Boeing made the system more aggressive and riskier. While the original version relied on data from at least two types of sensors, the ultimate used just one, leaving the system without a critical safeguard. In both doomed flights, pilots struggled as a single damaged sensor sent the planes into irrecoverable nose-dives within minutes, killing 346 people and prompting regulators around the world to ground the Max.
But many people involved in building, testing and approving the system, known as MCAS, said they hadn’t fully understood the changes. Current and former employees at Boeing and the Federal Aviation Administration who spoke with The New York Times said they had assumed the system relied on more sensors and would rarely, if ever, activate. Based on those misguided assumptions, many made critical decisions, affecting design, certification and training.
Au fond, ne s’agit-il pas de l’application à des outils « physiques » des préceptes et méthodes de l’industrie « immatérielle » ? Une idéologie de l’erreur/bug impossible, de la rapidité de mise sur le marché, de l’absence de réelle documentation, notamment d’une documentation qui ne dit pas « comment ça marche », mais « comment c’est conçu et pourquoi ».
While prosecutors and lawmakers try to piece together what went wrong, the current and former employees point to the single, fateful decision to change the system, which led to a series of design mistakes and regulatory oversights. As Boeing rushed to get the plane done, many of the employees say, they didn’t recognize the importance of the decision. They described a compartmentalized approach, each of them focusing on a small part of the plane. The process left them without a complete view of a critical and ultimately dangerous system.
The company also played down the scope of the system to regulators. Boeing never disclosed the revamp of MCAS to Federal Aviation Administration officials involved in determining pilot training needs, according to three agency officials. When Boeing asked to remove the description of the system from the pilot’s manual, the F.A.A. agreed. As a result, most Max pilots did not know about the software until after the first crash, in October.
L’informatique magique dans toute sa splendeur
But the plane wasn’t flying smoothly, partly because of the Max’s bigger engines. To fix the issue, Boeing decided to use a piece of software. The system was meant to work in the background, so pilots effectively wouldn’t know it was there.
That probability may have underestimated the risk of so-called external events that have damaged sensors in the past, such as collisions with birds, bumps from ramp stairs or mechanics’ stepping on them. While part of the assessment considers such incidents, they are not included in the probability. Investigators suspect the angle-of-attack sensor was hit on the doomed Ethiopian Airlines flight in March.
Bird strikes on angle-of-attack sensors are relatively common.
A Times review of two F.A.A. databases found hundreds of reports of bent, cracked, sheared-off, poorly installed or otherwise malfunctioning angle-of-attack sensors on commercial aircraft over three decades.
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