Well, while we await the full report the (much expanded) Seattle Times piece has a few interesting bits. The AoA sensor on the fatal flight had been recently replaced:
The replacement AOA sensor was a secondhand component supplied by a certified aviation repair shop, Xtra Aerospace in Miramar, Florida.
The part was faulty. On the flight directly before the fatal flight, the replacement sensor was off by 21 degrees from the one on the other side of the plane.
The report states that this difference indicates that the sensor “was most likely inadvertently mis-calibrated” during test and calibration in Florida. Xtra Aerospace’s procedures did not include an extra check required to validate the calibration.
The report notes that the FAA, which is supposed to oversee quality control at component suppliers missed this, and concludes that its “oversight was not effective.”
On Oct. 28, the day before the crash flight, following a series of cockpit warnings about airspeed and altitude, a maintenance engineer installed a new angle of attack sensor.
Though he was supposed to do an installation test to ensure it was correctly calibrated and installed, the maintenance records show no such test, the report found. The engineer did produce several photos of the flight display, which he claimed showed the test had been performed. But investigators could not confirm that the photos were taken in the plane that crashed and clearly suspected they were not.
“The investigation could not determine with any certainty that the AOA sensor installation (was) successful,” the report states.
On the Oct. 28 flight, the 21 degree angle of attack sensor fault set off the same series of events that would show up again a day later on the accident flight. The captain’s stick shaker went off immediately, the airspeed and altitude warnings appeared.
And after the pilot retracted the flaps, MCAS — assuming the angle of attack was too high because of the input from that one bad sensor — activated and began to push the nose of the aircraft down.
Since Boeing hadn’t informed airlines or pilots about MCAS, the captain and his first officer didn’t understand what was happening. But they were lucky in that a third pilot, another Lion Air first officer, was along for the free ride, sitting in the jump seat in the cockpit. That third set of eyes seems to have been crucial in helping the crew troubleshoot, stay calm and find a way out of the situation.
After discussion among the three of them, the captain flipped a pair of switches that cut off electrical power to the tail. That allowed him to regain control. When he flipped them back and the nose-down movements resumed, he cut off power again.
According to procedures, the pilot should have turned the plane around and landed as soon as possible. Instead, the crew flew on to their destination.
Upon landing, the captain reported only the issues that had shown up on his flight display: the airspeed and altitude warnings and a light indicating a difference in the feel of the control column. Fatally, he did not report the activation of the stick shaker, the way the stabilizer had pushed the nose down or his use of the cutout switches to resolve the problem, resulting in an “incomplete report.”
That omission, the report found, was critical to the maintenance engineer not realizing how serious the state of the plane was. It should have been grounded. But the next morning it would take off on its next flight, with the same pattern of faults, a different crew, and a deadly outcome.