Boeing on Wednesday specified software and flight deck display updates for the 737 Max following a briefing in Renton, Washington, with more than 200 airline pilots, technical leaders, and regulators. The updates, precipitated by two 737 Max crashes over the course of five months, center on the maneuvering characteristics augmentation system (MCAS) and related systems and equipment. The MCAS updates went through hundreds of hours of analysis, laboratory testing, verification in a simulator and two test flights, including an in-flight certification test with Federal Aviation Administration (FAA) representatives on board as observers, said Boeing.
One of the principal changes involves the angle of attack sensors, inputs from both of which the MCAS will now compare. If the sensors disagree by 5.5 degrees or more with the flaps retracted, the MCAS will not activate. An indicator on the flight deck display will alert the pilots.
If the MCAS activates in non-normal conditions, it will only provide one input for each elevated AOA event. Boeing said it knows of no failure conditions where the MCAS will provide multiple inputs. Finally, the MCAS can never command more stabilizer input than the pilots can counteract by pulling back on the column. The pilots can at all times override the MCAS and manually control the airplane. According to Boeing, the updates reduce the crew’s workload in non-normal flight situations and prevent erroneous data from causing MCAS activation.
Flight deck updates now include a formerly optional angle of attack disagree indicator and alert on the primary flight display. Neither Lion Air nor Ethiopian Airlines opted for the equipment in their Max cockpits.
Finally, Boeing has updated the Max’s computer-based differences training and manual review to accompany the software update. Boeing designed the course to provide 737 type-rated pilots with better understanding of the 737 Max speed trim system, including the MCAS function, associated existing crew procedures, and related software changes.
Under the new training regimen, pilots will need to review the flight crew operations manual bulletin, updated speed trim fail non-normal checklist, and a revised quick reference handbook.
Boeing continues to work with the FAA on the certification of the updates. It provided no timeline for expected certification or re-entry into service.