Boeing 737 MAX MCAS Nonsense



Southwest Airlines Boeing 737 MAX8 Parking Lot at Chicago Midway Airport (MDW)

Disasters and manias of our time:

  • Fukushima
  • p-hacking in the social sciences
  • SF Transbay Terminal welding and materials failures
  • Bitcoin speculation
  • and now Boeing MCAS.

So, let me get this straight about the Boeing 737 MAX MCAS sensors:

  1. MCAS is non-redundant – it relies on only one of two fuselage-mounted external Angle-of-Attack (AoA) sensors to control the most critical flight control, the stabilizer
  2. that can be damaged or frozen
  3. the 2 sensors can disagree with no warning to the pilot (except with a warning light in an optional package and compatible display device, which even Southwest initially didn’t have)
  4. that are not checked for zero on the ground
  5. and fuselage-mounted AoA sensors don’t provide true AoA except when wings-level
  6. behavior doesn’t match the certification documents, and no training materials provided.



The Angle-of-attack (AoA) sensor is located near the bottom of the foto. Note that it is exposed to physical damage and icing.

and …

  1. MCAS is activated on manual flight, where the pilot wouldn’t expect to have to disengage any “autopilots”. (But they would know what a stickshaker warning is.)
  2. MCAS is activated on flaps-up, thus immediately after takeoff, with little time for correction. Knowing how to disable MCAS would have to be a memory item, since reading the flight manual or checklist could easily take longer than the 25 seconds MCAS needs to hit the stop and become unrecoverable at low altitude (and in fact, one of the pilots was reading the flight manual at the time of impact.)
  3. MCAS can trim the stabilizer full nose-down to the stop (5 degrees) instead of the original FAA-approved 0.6 degrees, and will continuously to do so with a failed sensor like some kind of doomsday machine.

And this wasn’t adequately documented before revenue flying on the most popular airliner ever sold?

What’s interesting is that had a faithful simulator been created, this problem would have been found much earlier. But that would have raised re-certification and training questions.

MCAS was a bad proof-of-concept system, not at all ready for airline use. I can’t believe that not a single Boeing engineer noticed this design error.

Kudos to the crew of the first Lionair incident flight. The 3 pilots exercised good CRM and found the cutout switches in time to save their plane. (I recommended 3-man crewing for SE Asian flights in a previous post.)

“The FAA said it will mandate Boeing’s software fix in an airworthiness directive no later than April.” – but how does that fix the non-redundant sensor?

flyingmag.com: Lion Air Investigation Takes an Unexpected Turn
b737.org.uk: 737 MAX – MCAS
seattletimes.com: Flawed analysis, failed oversight: How Boeing, FAA certified the suspect 737 MAX flight control system
theaircurrent.com: The World Pulls the Andon Cord on the 737 MAX
Capt. Sullenberger on the FAA and Boeing: ‘Our credibility as leaders in aviation is being damaged’
The emerging 737 MAX scandal, explained
737: The MAX Mess (Very detailed notes)
American Airlines extends Boeing 737 Max flight cancellations
avweb.com: International Committee To Review MAX
avweb.com: Will Boeing Ever Dig Itself Out?

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