The Four-Second Catastrophe: How Boeing Doomed the 737 MAX

Andrew Tangel, Andy Pasztor and Mark Maremont 9 hrs ago

Almost as soon as the wheels of Ethiopian Airlines Flight 302 spun free from the runway March 10, the instruments in front of Capt. Yared Getachew went haywire.

© gary he/EPA-EFE/Shutterstock

The digital displays for altitude, airspeed and other basic information showed dramatically different readings from those in front of his co-pilot. The controls in Capt. Getachew’s hands started shaking to warn him the plane was climbing too steeply and was in imminent danger of falling from the sky.

Soon, a cascade of warning tones and colored lights and mechanical voices filled the cockpit. The pilots spoke in clipped bursts.

“Command!” Capt. Getachew called out twice, trying to activate the autopilot. Twice he got a warning horn.

Another powerful automated flight-control system called MCAS abruptly pushed down the jet’s nose. A computerized voice blared: “Don’t sink! Don’t sink!”

The pilots wrestled with the controls, desperate to raise the nose of their Boeing 737 MAX. Three times Capt. Getachew instructed co-pilot Ahmed Nur Mohammed, “Pull up!”

At the same time, a loud clacking warned the preoccupied pilots that the plane was flying too fast.

Four minutes into the flight, the pilots finally touched on the source of their problems, simultaneously calling out “Left alpha vane!”

Erroneous signals from that malfunctioning sensor tricked the onboard computers into believing the jetliner’s nose was angled too high, causing MCAS to push it down again and again.

It was too late. Flight 302 nose-dived at nearly the speed of sound, hitting the ground with such force that an airliner with 157 people aboard was largely reduced to fragments no bigger than a man’s arm.

Five months earlier, Lion Air Flight 610 had plunged into the Java Sea, killing 189 people, under similar circumstances.

Regulators have focused since the crashes on MCAS, its reliance on a single sensor and Boeing’s decision not to tell pilots about the new system. At the root of the miscalculations, though, were Boeing’s overly optimistic assumptions about pilot behavior.

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