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