Boeing 737 MAX Needs New Computer Systems to Meet Airworthiness Requirements

The troubled Boeing 737 MAX is one step closer to flying, but will require a complete overhaul on computer systems. The Federal Aviation Administration has submitted a proposed airworthiness directive, which would require new flight control computer software, MAX display system software, and other physical changes.

The Federal Aviation Administration is proposing a number of changes before the Boeing 737 MAX can fly once again, with most taking place in a cockpit. In a proposed airworthiness directive sent to the Office of the Federal Register, the agency is asking Boeing to completely change in-flight computer systems before the aircraft carries commercial passengers once again.

Airworthiness Directive Revolves Around Flight Control Computer and MAX Display System

The new airworthiness directive hinges on the improvement of two computer systems. After investigating the fatal crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 and completing test flights with Boeing, the agency is requesting changes to both the flight control computer and the MAX display system.

The updates would change when the maneuvering characteristics augmentation system (MCAS) can force the aircraft to pitch nose-down. Instead of taking input from a single angle-of-attack sensor (AOA), the flight control computer system would be updated to take readings from two AOA sensors. If it is not fixed, the FAA determined MCAS “could cause the flightcrew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and impact with terrain.”

”These revised flight control laws would use inputs from both AOA sensors to activate MCAS,” the proposed airworthiness directive reads. “This is in contrast to the original MCAS design, which relied on data from only one sensor at a time, and allowed repeated MCAS activation as a result of input from a single AOA sensor.”

The Lion Air 737 MAX-8, registration number PK-LQP, sits at Soekarno-Hatta International Airport (CGK). This aircraft would operate Lion Air Flight 610, which would ultimately crash, killing all 189 souls on board. Photo courtesy: Wikimedia Commons

In addition, the flight control computer update would require systems to alert pilots if there is a disagreement between the two AOA sensors. Investigations into the aircraft discovered some 737 MAX aircraft did not have this feature, which was not included erroneously. The disagreement alert would inform the pilots of potential calibration issues, or even a sensor failure.

“While the lack of an AOA DISAGREE alert is not an unsafe condition itself, the FAA is proposing to mandate this software update to restore compliance with 14 CFR 25.1301 and because 11 the flightcrew procedures mandated by this AD now rely on this alert to guide flightcrew action,” the proposal states. “As a result of the changes proposed in this AD, differences between the two AOA sensors greater than a certain threshold would cause an AOA DISAGREE alert on the primary flight displays.”

Finally, airlines would be forced to change the routing of the horizontal stabilizer trim wires in the aircraft. While it is not necessarily related to the computer overhaul, the change would bring the airframes in compliance with FAA wire separation safety standards.

Changes Could Cost Over $14,000 per 737 MAX

If all the changes in the proposed airworthiness directive are approved, the bill to airlines would cost an estimated $14,160 per aircraft. For Southwest Airlines, holds the largest domestic fleet of 737 MAX-8 airframes, the cost of compliance could come to a total of over $481,000.

None the less, Southwest is optimistic that they will fly the aircraft again before the end of the year. In multiple statements, the airline has committed to working with Boeing and the FAA to get the aircraft back in the operational fleet before 2021.

Once the notice of proposed rulemaking is published in the Federal Register, the public will have 45 days to comment on the recommended changes. While the FAA produced the document early in the spirit of full transparency, the full dockets and comments will be available at regulations.gov.

Feature image courtesy: The Boeing Company