The Inside Story of MCAS: How Boeing’s 737 MAX System Gained Power and Lost Safeguards (excerpt)
(Source: Seattle Times; published June 22, 2019)
By Dominic Gates and Mike Baker
Early in the development of the 737 MAX, engineers gathered at Boeing’s transonic wind tunnel in Seattle to test the jet’s aerodynamics using a scale model with a wingspan comparable to that of an eagle.

The testing in 2012, with air flow approaching the speed of sound, allowed engineers to analyze how the airplane’s aerodynamics would handle a range of extreme maneuvers. When the data came back, according to an engineer involved in the testing, it was clear there was an issue to address.

Engineers observed a tendency for the plane’s nose to pitch upward during a specific extreme maneuver. After other efforts to fix the problem failed, the solution they arrived at was a piece of software — the Maneuvering Characteristics Augmentation System (MCAS) — that would move a powerful control surface at the tail to push the airplane’s nose down.

This is the story, including previously unreported details, of how Boeing developed MCAS, which played a critical role in two airliners nose-diving out of the sky, killing 346 people in Ethiopia and off the coast of Indonesia.

Extensive interviews with people involved with the program, and a review of proprietary documents, show how Boeing originally designed MCAS as a simple solution with a narrow scope, then altered it late in the plane’s development to expand its power and purpose. Still, a safety-analysis led by Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds.

The revised design allowed MCAS to trigger on the inputs of a single sensor, instead of two factors considered in the original plan. Boeing engineers considered that lack of redundancy acceptable, according to proprietary information reviewed by The Seattle Times, because they calculated the probability of a “hazardous” MCAS malfunction to be virtually inconceivable. (end of excerpt)

Click here for the full story, on the Seattle Times website.


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