Boeing’s 737 MAX airliner has had a tumultuous time following its worldwide grounding in 2019. The 737 MAX was first delivered to an airline as recently as 2017, with Malaysian airline Malindo Air receiving a MAX8 and putting it into service in 2018.
As of March 2019, 387 of the airliners have been delivered to customers. However, two major accidents prompted authorities and airlines worldwide to ground the plane on an indefinite basis. The first involved the crash of a Lion Air flight travelling from Jakarta, Indonesia, to Bankga Island, also in Indonesia. 189 people died in the crash. The second accident involved an Ethiopian Airlines flight from capital Addis Ababa to Nairobi, Kenya. 157 people died in that crash.
In both cases, there were issues surrounding the reliance on a solitary sensor wrongly triggering a nose-down angle to fix a stall event that was never happening in the first place. In combination with this issue, insufficient training and inadequate instructions have also been cited.
Earlier this week, the United States’ Federal Aviation Administration (FAA) disclosed the specific conditions that Boeing must meet for the 737 MAX to be granted permission to fly commercially again.
In two documents, one labelled an Airworthiness Directive and the other labelled a Review of the Boeing 737 MAX, the FAA lists, in detail, what Boeing must alter in the airliner’s design and manufacturing so that it can fly passengers again.
These changes include the addition of a second sensor, called an Angle of Attack sensor (AoA), so that there is backup in case the first one malfunctions. Further, the two sensors will work in tandem, rather than sequentially. This will allow for the verification of the input from each sensor. In the event where one sensor disagrees with the other, the FAA has demanded a software update which will notify the pilots that this is the case.
The second requirement will see the plane’s Maneuvering Characteristics Augmentation System (MCAS) only engage once it has received input from the AoA sensor, rather than springing into action every single time. The repeated engagement of the MCAS was cited as one of the reasons for the crashes, where manual correction by the pilots was hindered by them having to figure out how to keep disengaging the automatic nose-down angle correction. Post-change, the pilots will be able to fly manually after the first and only MCAS engagement.
The FAA has also asked for changes to the flight deck, horizontal stabiliser trim, flight manuals, and operating procedures. The aerospace company has already overseen several 737 MAX test flights with a percentage of the proposed changes implemented and is aiming to bring the airliner back into commercial use within the current year.