Much like tapping the brake pedal in a car to disengage cruise control, a sharp tug on the controls of older models of Boeing Co.'s 737 used to shut off an automatic trim system that keeps the plane flying level, giving the pilot control.
But Boeing disabled the "yoke jerk" function when it brought out the 737 Max, the latest version of its top-selling jet — and many pilots were unaware of the change, aviation experts said.
The difference may help explain why pilots struggled to keep their aircraft climbing after takeoff on two fatal 737 Max flights less than five months apart that left a total of 346 people dead.