The reason they died on activation #21 and not #1 is that the effects are cumulative. The stabilizer position was graphed on that preliminary report (see: pit

The reason they died on activation #21 and not #1 is that the effects are cumulative. The stabilizer position was graphed on that preliminary report (see: pitch trim position). There was a slight trend towards nose down pitch, but no, at the time they lost control there's a sharp decrease in pitch that doesn't correlate with MCAS. If you look at the "trim manual" line you'll see that the pilot flying was continuing to input nose up pitch on the switches to no effect. Something changed and it wasn't simply that the pilot was overridden by MCAS. After 21 even MCAS continued to counter the pitch up inputs as the stabilizer continued to contribute additional nose down pitch. I agree that the jury is still out as to whether it’s a sensor issue per se or some sort of ADC or data transmission issue. To be clear I highly doubt the alpha vane was defective. It's a possibility, but look at that graph. The left "angle of attack indicated" mirrors the right one almost exactly except that there's a near constant twenty degree offset. If that's a sensor problem in two separate sensors I'll pull a Werner Herzog and eat my freaking shoe.