[drtillberg]

I've read several of these articles about the MAX and I'm not seeing the explanation for how allowing MCAS to fly the plane only on input from AOA sensors (1, 2 or 5) is different from asking pilots to fly the plane with a fogged-up windscreen. Why not cross-check against the true horizon, for example? Doesn't seem safer to unnecessarily disregard context.

[mikeash]

MCAS only exists to paper over a small handling deficiency. Apparently nobody (at least nobody with the power to force a change) thought that it could pose a safety problem. It’s not safety critical, so who cares if it fails? Except that it can fail in a way that crashes the plane.

[inferiorhuman]

MCAS only exists to paper over a small handling deficiency.

Per the article MCAS was originally intended to handle uncommon edge cases but was extended to cover additional (low speed) deficiencies. This expanded scope is what made MCAS as problematic as it is because it did away with the second input (accelerometer) and expanded the authority dramatically (from something like 0.6 degrees to 2.4 degrees of stabilizer movement).

[salawat]

The problem occurred in that that sensor had a privileged (unoverridable) pipeline to the horizontal stabilizer.

The pilots knew something was going wrong. That wasn't the issue. The issue was that the bloody thing could mistrim the plane to the point of nigh irrecoverability, and no one knew enough about it until two planes full of people plunged out of the sky.

The plane may be able to fly just fine; but the way this thing was developed and brought into mainstream use had critical problems in terms of essential information being communicated.

All the decisions and motivations behind these lack of communication have to some point been traced back to trying to circumvent regulations in order to prop up share price by scoring sales of a new airframe of comparable efficiency to the a320neo.

[chipsa]

True horizon has nothing to do with angle of attack. Angle of attack is the direction the wind is coming from relative to the aircraft. It's possible to have a nose up attitude relative to the horizon, and have the actual aircraft motion be downwards at 10,000 feet per minute.