Remember the 737 MAX, Boeing’s latest edition of the venerable 737 line of commercial airliners?  You are forgiven if the answer is no or vaguely.   The MAX hasn’t flown since it was grounded indefinitely in March 2019 following two accidents that claimed the lives of 346 passengers and crew.

Maneuvering Characteristics Augmentation System (MCAS)

Investigations pointed to the plane’s Maneuvering Characteristics Augmentation System (MCAS) as the primary cause of both accidents.   To increase fuel efficiency,  Boeing equipped the 737 MAX to with larger, heavier, and more powerful CFM LEAP-1B engines and located them higher and farther forward on the wing.  That changed the aircraft’s aerodynamics and created a tendency of the nose to pitch up.

To counter the changed aerodynamics, Boeing developed MCAS to make it handle like other 737s.  That allowed pilots of earlier 737 models to transition to the MAX without additional training.  It was easier to sell the MAX if airlines didn’t have to factor additional pilot training expenses into their calculations when buying the plane.


As incredible as it sounds, pilots didn’t even know MCAS was installed on their aircraft.  During certification Boeing removed a description of MCAS from the MAX flight manuals.  Pilots had no idea how to counteract a malfunction in a system they didn’t even know existed.

Boeing’s other major flaw was tying activation of MCAS to only one of at least two  angle of attack sensors.  A single faulty angle of attack sensor could trigger MCAS in  situations where it was not needed.  That violates the principle of redundancy, a fundamental concept in commercial aviation safety.

FAA Notice of Proposed Rulemaking

Last week. the Federal Aviation Administration (FAA) issued a 36-page notice of proposed rulemaking containing a proposed airworthiness directive (AD) that is designed to return the Boeing 737 MAX safely to the skies.  The document is open for public comment for 45 days.

The AD proposes changes in four areas:  new MCAS flight-control software, flight manual changes, a new MAX display system, and rerouting wiring for the horizontal stabilizer.

The FAA wants new MCAS flight control software installed to prevent any  undesired or inappropriate MCAS activation.  MCAS will now have to receive data from two angle of attack sensors.  Further, before aircraft can return to service, their angle of attack sensors must be tested in operational readiness flights.


Flight manual changes create new procedures to ensure pilots are aware of any sensor data or systems they might have to deal with in an emergency.

A new display and software package will generate an angle of attack disagree alert to warn pilots if there are problems with either or both angle of attack sensors. The FAA wants to ensure there is no possibility of confusion about sensor data going forward.

Changes to the horizontal stabilizer (the horizontal wing on the tail) trim wiring conform to routing standards implemented since the MAX entered service.


Additional Required Actions

Don’t expect the 737 MAX to be flying before the end of the year.  Completion of all these steps would not mean that the 737 MAX can return to commercial service.  The FAA has identified seven other major steps that have to be made before this could happen. These include the review and approval of the proposed future training for flight crews by the FAA Flight Standardization Board (FSB) and the Joint Operations Evaluation Board (the latter including representatives of regulators from Brazil, Canada and Europe).

After those steps, the FAA would then have to rescind its grounding order for the aircraft and issue new airworthiness certificates for each and every new 737 MAX assembled during the period that the type was grounded.

Final Thoughts

I am (or was) a big Boeing fan.  The 787 Dreamliner remains my favorite airliner.  However, Boeing mismanaged the 737 MAX program from the beginning.  Using data from only one angle of attack sensor to activate MCAS and not even mentioning MCAS in the original flight manual were major errors that an airplane manufacturer should never make.

I can only conclude that Boeing was more interested in sales and profits than the safety of the public.  That damning conclusion is reinforced by the Boeing’s insistence on keeping the MAX in the air after the first accident.

The FAA is also deserving of criticism for its laissez-faire approach to regulation that gave Boeing a lot of control over the certification process and its failure to ground the MAX before the second accident.  The FAA was even the last national aviation body to ground the MAX following that accident.  Boeing and the FAA lost a lot of credibility that will be tough to win back.

I’ll probably fly on the 737 MAX once it is recertified, but I may wait a few months to see how things go.  What are your thoughts about the 737-MAX?  Will you fly on it?

All photos from Boeing