Boeing 737 Max and the many human errors that brought it down

The first sign of trouble appeared just after takeoff.

Inside the cockpit of PK-LQP, a brand-new Boeing 737 Max belonging to Lion Air, the stick shaker on the captain’s side began to vibrate. Stick shakers are designed to warn pilots of an impending stall, which can cause a dangerous loss of control. They’re unmistakably loud for that reason.

But the airplane was flying normally, nowhere near a stall. The captain ignored it.

About 30 seconds later, he noticed an alert on his flight display — IAS DISAGREE — which meant that the flight computer had detected a sensor malfunction. This required a bit more attention.

A modern-day passenger airplane is less like a racecar and more like a temperamental printer: you spend more time monitoring and checking systems than you do actually driving the thing. So the captain passed control of the aircraft to the first officer and began the troubleshooting process from memory.

Like all commercial aircraft, the Boeing 737 Max has multiple levels of redundancy for its important systems. In the cockpit, there are three flight computers and digital instrument panels operating in parallel: two primary systems and one backup. Each system is fed by an independent set of sensors. In this case, the captain checked both instrument panels against the backup, and he found that the instruments on his side — the left side — were getting bad data. So with the turn of a dial, the captain switched the primary displays to only use data from the working sensors on the right side of the airplane. Easy

All of this took under a minute, and everything appeared to be back to normal.

At 1,500 feet of altitude, the takeoff portion of the flight was officially complete, and the first officer began the initial climb. He adjusted the throttle, set the aircraft on its optimal climb slope, and retracted the flaps.

Except the airplane didn’t climb. It lurched downward, its nose pointed toward the ground.

The first officer reacted instinctively. He flicked a switch on his control column to counteract the dive. The airplane responded right away, pitching its nose back up. Five seconds later, it dove once again.

The first officer brought the airplane’s nose up a third time. It pitched back down.

There was no memorized checklist that seemed to apply to this situation, so the captain reached for the airplane’s Quick Reference Handbook (QRH). The QRH is a series of simple checklists that are designed to help pilots rapidly assess and manage “non-normal” situations. The idea is that Boeing has thought of every conceivable thing that might happen to one of its airplanes, and it has included all of them in the QRH. Basically, it’s more troubleshooting.

But nothing in the QRH seemed to apply, either.

Over the next six minutes, as the first officer struggled to control the airplane and the captain searched for the right checklist, PK-LQP climbed and dove over a dozen times. At one point, the airplane pulled out of a 900-foot dive at an airspeed of almost 375 mph, which is uncomfortably close to the 737’s “redline” of 390 mph.

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