Two crashes within a few short months of each other,
hundreds dead, experienced crews aboard each and a known absent control
redundancy? This airplane needs another look by embarrassed regulators.
The Boeing 737 MAX is a further lengthened version of the
most popular airliner ever conceived, the 737. But the differences in the MAX
are more than just size. The MAX is so stretched that a control intervention
system, The Maneuvering Characteristics Augmentation System, was included that
figured into the crash of the LIONAIR JT 610 crash in Indonesia. In that crash,
an angle of attack sensor malfunction was implicated as well as a failure by
Boeing to provide adequate differences training materials (documents to advise
flight crews how operating the MAX differs from other 737s).
While LIONAIR maintenance and pilot error was charged by
Boeing, as it always does after an accident, it turns out that normal emergency
techniques for this control system malfunction do not work.
It appears now that absent proof that foul play or a different
mechanical malfunction brought this airplane down, this Ethiopian Airlines 737
MAX accident must be a trigger for a Special Airworthiness Review to see if the
regulations for certification were not given short shrift.
For example, the Federal Aviation Regulations require
control system redundancy so no single failure can cause a crash. In the new MAX
design, there are two angle of attack sensors but only one supplies the needed
critical information to the flight control computer at any one time. That may
be a violation of the redundancy requirement and both systems operating
properly with a comparator of the health of the two should have been required.
But there appears to be an ugly side to this aircraft. The
Maneuvering Characteristics Augmentation System in the MAX pitches the nose
down when the a system senses an angle of attack higher than required for
normal flight or one that would result in an aerodynamic stall. Since the
system is a required control system for dispatch, by making only one angle of
attack sensor required and indeed used at a time, Boeing hedged on the likely
failure of two AOA’s at the same time and got it certified.
Now the FAA, the agency that certified the aircraft will
fall all over itself to deny that the MAX doesn’t meet the regulations but it
said the same thing when three B-737s crashed from a rudder control problem
that the FAA denied existed. More than 600 people lost their lives while the
FAA defended its actions and stood in Boeing’s shadow until the NTSB
reluctantly and due in part to the work of Arthur Alan Wolk required a reliably
redundant rudder control system.
Until the cause of this latest crash is determined, the MAX
should be grounded and a bottom up review made to see how this new band aid
system fails, how its failure can be annunciated to the flight crew and how it
can be stopped once it runs away.
It is no coincidence that both aircraft crews lost control
close to the ground and unless something else is quickly identified as the
cause, the Maneuvering Characteristics Augmentation System must be a suspect.
Something about the MAX’s design required this unheard of mechanical
intervention in the normal control of the Boeing 737, literally taking control
away from the crew so the airplane doesn’t crash. The fact that it is known
that this supposedly lifesaving system may itself cause a crash makes a careful
re-examination of it appropriate before 600 people are lost instead of the more
than 300 dead already.
Arthur Alan Wolk 3/10/2019
