The controversial MCAS system of the Boeing 737 MAX

Given the current situation afterés of the unfortunate accident of Ethiopian Airlines flight ET302 and its apparent connectionón with the Lion Air incident 610 Some months ago, It is relevant to inform about the particularities of the máwith modern avión of Boeing with respect to its predecessors and especially the controversial MCAS system of the Boeing 737 MAX.

post writer by: Juan Matheus

The 737 is he “work horse” the Boeing, it's the avión más sold history and carries produciégoing around 40 años. He's a grandfatherón very versáuseful in the segment of 120-200 passengers and its range has increasingly improved más así as its capacity and the avióunique in general.

Su más recent versionón, the so-called MAX, was Boeing's response to the updateón of your competitor, the Airbus to the A320NEO. Both updates to the program have allowed an aviósingle-aisle, two-engine aircraft capable of transatlantic flightsáAtlantic and many new route possibilities have been opened that were not possible before and the market did not allow for operating smaller aircraft.ás large. Both the 737MAX and Airbus A320/321 NEO programs focused on improving engines.ón and lower fuel consumption, also increasingén the range. In the case of the Airbus NEO it means “New Engine Option”, that is to say “new optionónumber of engines”.

Being an updateón “smaller” to a successful and proven model, Boeing logró build up an impressive order book, with thousands of MAXs to be produced and delivered (más de 5.000). Es, definitely, a successful program. One of the main points to convince the airlinesíwas that the MAX assumesíto a transición simple for the pilots of the 737NG that was sought to replace. It has been reported that the introductory courseóThe flight to the MAX lasted an hour and the flight manual did not includeíand informationón about software changes, among those, the MCAS.

MCAS

EL Boeing 737 MAX in their versions -8 and -9, Carries the new CFM LEAP-1B turbofan engine. This engine is not only 15% más efficient, spaghettién is considerably más grande. Esto obligeó to be placed más ahead than in the NG, causing an unwanted side effect: The MAX trendíto raise the nose too much, engine product sás large located más forward.

as already we have previously discussed, I saw oneón has a áfrom the corner of the attack máximo (called crítico) in which the air passing through the wing profile is “To stop” and turbulence is created and péloss of liftón. If the MAX at takeoff caníto reach fácil and involuntarily áangles of attack críticos, habíto find a way to correct the problem.

Then, Boeing decidió introduce a software called MCAS or “Maneuvering Characteristics Augmentation System”. The goal of the software was to use the sensor readings áangle of attack and “correct” tilt itón of the aircraft if it approached the ácr angle of attackítico. This was done through the use of the stabilizers that are located on the sides of the timón, at the rear. If the nose subítoo much, the stabilizer was going down, carrying out what is called “trimming”.  Reports from pilots suggest that Boeing ignoredó the MCAS in pilot training and it has been possible to know what they thinkíwhat was it “flood crews with informationón unnecessary”.

¿MCAS is responsible for the accidents in Indonesia and Ethiopiaía?

Todavíwe cannot affirm it categoricallyórichly but apparently both incidents wereían related. Data from the black boxes suggests that the pilots struggled to stabilize the ship and the computer insistedó on “stick your nose down”. Although everything avión has today in díto a sensor of áangle of attack, and apparently the designñor of the two sensors in the MAX no varía of the versionón anterior, seemíbecause MCAS software under special circumstances that must be replicated, misinterprets the AoA sensor reading (Áangle of attack) and does not allow the pilot to disengage the autopilotático and make a “override manual”.

In the cabin there is a control to deactivate the MCAS but in the case of Lion Air it seems the crewón was not aware that the system existedíoh and what couldíto disconnect manually. Afterés of that accident Boeing issuedó a mushroomín where training on this function was reinforcedón.

¿Perhaps the crewóET302 n did not retrain?

The CEO of Ethiopian Airlines has said that afterés from that accident, their pilots if they were instructed on MCAS and how to turn it off. Además, before this new accident, Boeing was already working on an updateón the software. This does not allow us to conclude for now that MCAS was responsible, although the err behaviorático of the ancestoróEthiopian flight shows many similarities with Lion Air flight, and the stabilizers were found pointing downwards.

Although we cannot draw definitive conclusions yetía, the order to leave all the MAX on the ground was a wise move. Many analysts and pilots believe that the problem is that these planes are too “computerized”, limiting the work of the pilots and in this case, even preventedéearrings.

The engineeríMany times it must be subject to economic factors.ómonkeys and apparently Boeing preferredó use a solutionón extremely and unnecessarily complex by not sitting down at the drawing board and redesigningñar the fuselage and wing of the 737 to properly accommodate the CFM LEAP-1B and does not giveñar to aerodyneámica. This was going to take más time and possibly, costaría más to the manufacturer and the aerosolídenies, but it seems that it would have been a step closeráIt makes sense.