Original sentence: Boeing also offered a free option to enable a cockpit display of actual AoA value.Boeing began software changes with several goals: to make MCAS less susceptible to sensor or computer failure; to ensure the system cannot override pilot control; and to enable an AoA  "disagree" alert on all aircraft, which indicates AoA sensor malfunction.Boeing previously charged for the option, ordered by few airlines, resulting in inoperative disagree alerts on most of the MAX fleet, including both doomed aircraft.Pilots were not informed about MCAS until after the Lion Air accident, when Boeing published an update to the flight manual, enforced by an FAA airworthiness directive
Edited sentence: Ethiopia’s crew went against procedures, when they re-engaged the stab trim system despite Boeing highlighting the caution against doing that.Pilots were not informed about MCAS until after the Lion Air accident, although Boeing didn’t have to inform pilots, in the 737, any uncommanded nose pitch down.The procedure for stopping unwanted trim has been known since 1967