Free Flight, Free Speech

V12 wrote:How many AoA sensors has madmax ? I hope, minimal 2. Why MCAS software not doing cross check of outputs from sensors and when detect too much differences will not disable itsef with strong aural warnings ?

Like all 737s, the MAX actually has two of the sensors, one on each side of the fuselage near the cockpit. But the MCAS was designed to take a reading from only one of them.

Lemme said Boeing could have designed the system to compare the readings from the two vanes, which would have indicated if one of them was way off.

Alternatively, the system could have been designed to check that the angle-of-attack reading was accurate while the plane was taxiing on the ground before takeoff, when the angle of attack should read zero.

“They could have designed a two-channel system. Or they could have tested the value of angle of attack on the ground,” said Lemme. “I don’t know why they didn’t.”

After the Lion Air crash, 737 MAX pilots around the world were notified about the existence of MCAS and what to do if the system is triggered inappropriately.

Boeing insists that the pilots on the Lion Air flight should have recognized that the horizontal stabilizer was moving uncommanded, and should have responded with a standard pilot checklist procedure to handle what’s called “stabilizer runaway.”

If they’d done so, the pilots would have hit cutoff switches and deactivated the automatic stabilizer movement.

Boeing has pointed out that the pilots flying the same plane on the day before the crash experienced similar behavior to Flight 610 and did exactly that: They threw the stabilizer cutoff switches, regained control and continued with the rest of the flight.


However, pilots and aviation experts say that what happened on the Lion Air flight doesn’t look like a standard stabilizer runaway, because that is defined as continuous uncommanded movement of the tail.

On the accident flight, the tail movement wasn’t continuous; the pilots were able to counter the nose-down movement multiple times.

In addition, the MCAS altered the control column response to the stabilizer movement. Pulling back on the column normally interrupts any stabilizer nose-down movement, but with MCAS operating that control column function was disabled.

These differences certainly could have confused the Lion Air pilots as to what was going on.

Since MCAS was supposed to activate only in extreme circumstances far outside the normal flight envelope, Boeing decided that 737 pilots needed no extra training on the system — and indeed that they didn’t even need to know about it. It was not mentioned in their flight manuals.

For many new airplane models, pilots train for hours on giant, multimillion-dollar machines, on-the-ground versions of cockpits that mimic the flying experience and teach them new features. But in the case of the Max, many pilots with 737 experience learned about the plane on an iPad.


“We would have liked to have had a simulator” from the start, said Jon Weaks, the president of the Southwest Airlines Pilots Association. “But it wasn’t practical, because it wasn’t built yet.”

IAHM-COL wrote:facepalm! an iPad? is it running FG?