UPDATE 4-Boeing did not disclose 737 MAX alert issue to FAA for 13 months

The U.S. planemaker has been trying for weeks to dispel suggestions that it made airlines pay for safety features after it emerged that an alert designed to show discrepancies in Angle of Attack readings from two sensors was optional on the 737 MAX. Erroneous data from a sensor responsible for measuring the angle at which the wing slices through the air – known as the Angle of Attack – is suspected of triggering a flawed piece of software that pushed the plane downward in two recent crashes. In a statement, Boeing said it only discovered once deliveries of the 737 MAX had begun in 2017 that the so-called AOA Disagree alert was optional instead of standard as it had intended, but added that was not critical safety data.