he never went back and fixed the error. >> narrator: mark forkner wouldn't speak to us. charges in federal court. his lawyer told the "times" reporters that his communications with the f.a.a. were honest and that "he would never jeopardize the safety of other pilots or their passengers." ♪ ♪ when boeing engineers expanded the mcas system, they included a feature that would make it particularly dangerous. >> planes have millions of parts in them. and there's one little one on the 737 that sticks out of the fuselage. >> see that little black circle there? that is called... >> ...the angle of attack sensor. >> on the 737 max, it had the power to trigger mcas. >> it's the a.o.a. sensor that is one of the crucial parameters to the computer to tell the plane that it's in a perilous condition. >> the angle of attack senr would activate mcas by telling the system that the plane's nose was too high and then mcas would try to push the nose down. >> but if this sensor is broken, for whatever reason, mcas never realizes, and so it keeps pushing the nose of the plane down, over and o