Boeing confirmed Tuesday that it won’t submit final paperwork to the Federal Aviation Administration for a flight control software update for the 737 Max until “the coming weeks” as opposed to the March 29 target it cited last week. The concession came soon after the FAA issued a notice on its Twitter page on Monday suggesting a delay.
“We are working to demonstrate that we have identified and appropriately addressed all certification requirements and will be submitting for FAA review once completed in the coming weeks,” said Boeing. “Safety is our first priority, and we will take a thorough and methodical approach to the development and testing of the update to ensure we take the time to get it right.”
The company has worked on the fix since last November, soon after a Lion Air 737 Max 8 crashed into the Java Sea, killing all 189 aboard. While the so-called shutdown of the U.S. federal government early this year interrupted the process due to a lack of available FAA representatives, the job took on far more urgency with the crash on March 10 of an Ethiopian Airlines Max 8 outside Addis Ababa, killing 157.
On March 27 Boeing 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 center on the Max’s maneuvering characteristics augmentation system (MCAS) and related systems and equipment.
One of the principal changes involves the angle-of-attack (AOA) 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.
In the previous design, certified by the FAA under an amended type certificate, a fault in a single angle of attack sensor could trigger the MCAS to send the airplane into an uncommanded nose-down attitude. Investigators believe both Max 8 crashes happened under similar circumstances and involved repeated automatic MCAS commands.
In the new design, if the MCAS activates in non-normal conditions, it will provide just one input for each indication of an AOA problem. Finally, the MCAS can never command more stabilizer input than the pilots can counteract by pulling back on the control column, meaning 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 a 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.
However, the FAA still appears unconvinced that Boeing has demonstrated the changes are ready to undergo the certification process. “Time is needed for additional work by Boeing as a result of an ongoing review of the 737 Max flight control system to ensure that Boeing has identified and appropriately addressed all pertinent issues,” the agency said. “Upon receipt, the FAA will subject Boeing’s completed submission to a rigorous safety review. The FAA will not approve the software for installation until the agency is satisfied with the submission.”