This Wednesday (27/03) Boeing officials released more details about the new software update for the 737 MAX, after conducting the first tests
The new update will be incorporated to improve the characteristics of the MCAS system (Maneuvering Characteristics Augmentation System), but this is not a problem, Boeing justifies that this system needs to exist to eliminate the possibility of the pilot entering a stall condition during takeoff.
“This combination of changes will eliminate the chance of erroneous data causing an MCAS activation”, said a Boeing executive who declined to be identified.
Boeing has previously pointed out that this new software completely prevents the situation suffered by Lion Air pilots from being repeated again.
"We're going to do everything we can to make sure accidents like this never happen again," said Mike Sinnett, vice president of product strategy and future airplane development.
The First Rule dictates that MCAS will operate by directly analyzing data from at least two angle-of-attack sensors, located on the nose of the 737 MAX. If the inputs between the sensors vary by more than 5,5º, the system will be deactivated.
Basic principle of operation of the MCAS system.
This first rule implemented by Boeing avoids the situation that occurred on Lion Air flight JT610, when the MCAS computer acted to compensate the angle of attack from a sensor that reported an angle of attack greater than 30º, while another sensor reported an angle of just 10º, normal during takeoff.
Interestingly, this should be a basic engineering rule, but Boeing did not implement it before, during the 737 MAX test program, and the FAA certified the software with this flaw.
Most of the “failures” that have occurred with the MCAS system have been due to the characteristics of this first rule.
the second rule it is deeper, as it operates during the time the sensor sends the same position to the computer. If the system reports a high angle of attack for a long time, the MCAS system is deactivated and the parameters are reset. Despite this, if in the initial seconds the two sensors report a very high angle of attack, the MCAS system comes into action to protect the plane from entering a stall condition due to angle of attack.
the third rule is in the list of MCAS commands, now the system does not act on the horizontal stabilizer so quickly, this allows the pilots to understand the system's performance, and implement measures to deactivate the MCAS before the plane loses altitude.
Boeing has also changed some MCAS deactivation possibilities. The pilots can deactivate the system through any command on the control column, in addition, if the pilot is in altitude reduction procedure, as in the landing, the MCAS system does not come into operation.
“The [stick] column will always be able to override the MCAS input with enough maneuverability that the aircraft can still climb”, a Boeing engineer told the FlightGlobal Portal.
Boeing insisted that pilots can disable MCAS by following existing procedures, such as operating the stab trim-disable switches located near the thrust levers. The electrical control system for the trim on the stick will also be capable of disabling any MCAS actuation.
Pilots will have a visual indication on the screens of deviations in the sensors' angle of attack reading, as well as when the MCAS system is activated.
Pilot training must be reinforced and has already been updated by Boeing.
After the FAA approves the fix, Boeing said it will ship the software update to customers. It takes a few days to install and longer for training and testing, the company said.
By the end of this week, Boeing plans to send software updates to airlines, but chose not to disclose a likely date of return of the 737 MAX to commercial flights.
