Changes to the 737 MAX / Additional Updates
Additional Updates
What was addressed prior to the airplane returning to service?
During the review and testing process, a few issues were discovered that did not directly relate to the Maneuvering Characteristics Augmentation System (MCAS) or the accidents. These items were addressed on every airplane before it returned to service.
1 Developed software updates to address theoretical horizontal stabilizer issue
During testing, the team simulated what would happen in the event of various potential fault conditions. These identified a theoretical combination of faults that could lead to a runaway stabilizer condition. Although this condition has never occurred during the 200 million hours of flight operations on any 737 airplane, new software was developed, tested and certified to ensure that it can never happen. Updated software was loaded on all airplanes before they returned to service.
2 Determined solution to modify some wiring to meet regulators’ requirements
The regulators’ comprehensive review process included a robust examination of the airplane’s horizontal stabilizer control system. During the review the team determined that some of the wiring associated with the system wasn’t separated as far apart as required. All airplanes were modified to meet this requirement before returning to service. In some cases, we performed this task for our airline customers; in others, we provided them with all of the technical documentation and materials they needed to do the work themselves.
3 Checking stored airplanes for Foreign Object Debris (FOD)
FOD can be an unintentional byproduct of the airplane production process. During routine maintenance on airplanes in storage, we found some instances of FOD. We immediately inspected all of the stored airplanes for FOD and shared inspection recommendations and detailed instructions with customers storing their own airplanes. We also enhanced our training and procedures to reduce the likelihood of FOD. All airplanes underwent a FOD inspection prior to returning to service.
4 Autopilot updated
The autopilot’s response to slow airspeed situations has been changed such that the autopilot will disconnect upon reaching significantly low speed. The disconnect alerts the flight crew to correct the situation by recovering airspeed manually. Updated software was loaded on all 737-8 and 737-9 airplanes before they returned to service.
Will there be additional changes in the future?
All of our airplane programs include a process for continuous product improvement. Neither of the following items were considered by regulators to be required for the safe return to service but will be addressed as we go forward.
Increased Angle of Attack (AOA) integrity
One regulator requested that we also consider future action to further increase AOA integrity. The regulator did not consider this a requirement for the airplane’s safe return to service. Our teams are developing enhanced angle of attack, a series of advancements including new software monitors to evaluate and detect erroneous angle of attack data. It will simplify how information is presented, and hardware changes will allow crews to inhibit persistent alerts derived from erroneous readings.
Additional crew alerting testing
Following return to service, Boeing and key regulators will continue to engage in studying the human factors associated with the crew alerting features on new models of the 737.