Boeing has issued a software update to the Maneuvering Characteristics Augmentation System (MCAS) on the 737 MAX.

The 737 MAX’s anti-stall system is being looked at by investigators as a possible factor in the fatal crash of a Lion Air jet in Indonesia in October and an Ethiopian Airlines plane earlier this month, although a Boeing official is quoted by Reuters as saying that the software upgrade is “100 per cent independent of the timing of the Ethiopian accident” and was about making the software more “robust”.

MCAS is designed to activate in manual flight, with the aeroplane’s flaps up, at an elevated Angle of Attack (AOA).

Boeing’s MCAS software update aims to provide additional layers of protection if the AOA sensors provide erroneous data. The flight control system will now compare inputs from both AOA sensors. If the sensors disagree by 5.5 degrees or more with the flaps retracted, MCAS will not activate. An indicator on the flight deck display will alert the pilots.

If MCAS is activated in non-normal conditions, it will only provide one input for each elevated AOA event.

“There are no known or envisioned failure conditions where MCAS will provide multiple inputs, Boeing says.”

Following the update, MCAS can never command more stabiliser input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to have the ability to override MCAS and manually control the aeroplane.

Boeing says: “The software was put 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.”

Boeing is working with the FAA and other regulatory agencies on the certification of the software update.

Boeing has also created computer-based training to accompany the software update.

“We are going to do everything that we can do to ensure that accidents like these never happen again,” Mike Sinnett, vice president for product strategy development is quoted as saying.

Boeing 737 MAX planes remain grounded following the recent Ethiopian Airlines accident.

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