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An Update on the Boeing 737 MAX

Boeing and regulators are soon to roll out a fix for the Boeing 737 MAX to prevent future fatal crashes.

In the past five months, there have been two eerily similar incidents involving the 737 MAX. On October 28, a 737 MAX operated by Lion Air crashed into the sea minutes after taking off from Jakarta, killing
189 people. The plane’s “black box” was only recovered in January. More recently on March 10, another 737 MAX operated by Ethiopian Airlines flying from Addis Ababa to Nairobi crashed and killed 157. According to satellite data and data from the wreckage of the second plane, both flights had similar problems prior to crashing. The planes would veer up and down several times before finally entering a fatal nosedive. While the causes of the crashes still aren’t fully understood, many of the relevant details have become widely known over the past weeks and months.

Not all 737s are MAXs. The first variants of the Boeing 737 flew in 1967, and over the decades new versions have been developed. While the 737 was a very successful plane, in 2010 Boeing was actually planning on creating a totally new aircraft to replace the 737. That changed in 2011, when Airbus announced a new variant of its A320: the A320neo. As demand for the A320neo began to rise, Boeing decided it needed a competitor as soon as possible and designing a new plane would take an entire decade. So they changed plans, opting to create yet another 737 variant. The 737 MAX program had begun.

One of the ground rules for the MAX design was that it had to be as similar as possible to the earlier 737 models. In particular, the piloting experience needed to be similar: otherwise longtime 737 pilots would need to be retrained before flying the MAX, increasing the cost for airlines to deploy the aircraft. However, competing with the A320neo required the MAX to have larger, more fuel-efficient engines than previous generations of the 737. This would cause the MAX to tip upwards far too often, which risks the plane going into a stall.

To correct this issue, Boeing developed the Maneuvering Characteristics Augmentation Algorithm (MCAS). One of its tasks would be to automatically pull the plane downward when the aircraft’s Angle
of Attack (AoA) sensors detected a significant tip upwards. The MCAS would operate silently in the background, keeping the plane at the expected angle, and pilots would be none the wiser. Boeing and
aviation regulators both agreed that MCAS-specific training would not be necessary for pilots. Until the Lion Air crash, most pilots were left in the dark about MCAS.

The 737 MAX entered service in 2017, after just six years of development. Airlines ordered over four thousand of the planes, making it Boeing’s fastest selling plane. However, not all the 4700 had the same features: Boeing and other aircraft manufacturers make lots of money selling optional customizations of their products. The customizations of a 737 MAX could cost as much as two million US dollars: about five percent of the aircraft’s full cost. Many of these features are aesthetic, or for passenger comfort. However, some of these “optional features” are safety features. For example, the Japanese require aircraft to have an extra fire extinguisher in the cargo hold. Airlines not operating in Japan sometimes decide not to pay for this feature.

Manufacturers and airlines alike are pretty secretive about this: Boeing has not made a full list of 737 MAX customizations available to the public. However, it has recently surfaced that some of the
customizations not purchased by Lion Air or Ethiopian Airlines would have been helpful during the crash. One such feature is an indicator showing the reading from the Angle-of-Attack (AoA) sensors. Another is a “disagree light”, which would be activated when the two AoA sensors are providing different readings.

With all these details, a more detailed scene of the crashes begins to emerge. First, the plane starts slightly dipping down, and pilots attempt to pull the plane up again. The plane dips down, and the pilots realize they are fighting an automated system for control. They try yanking the control column to put the machine under manual control. However a few minutes later, the MCAS reasserts control over the jet and it tips down again, perhaps because of a malfunctioning AoA sensor that the pilots had no way to detect.

Prior to the Lion Air crash, the doomed plane had MCAS-related difficulties on 4 flights. One of these non-fatal incidents was just two days prior to the crash. An extra third pilot would correct the problem by disconnecting the MCAS system. However, on March 28 that particular pilot was not onboard, and the remaining crew did not have enough time to debug the problem. They desperately yanked the control
column several times, with as much as 100 pounds of pressure. The MCAS kept tipping the nose down all the same until the plane nosedived right into the sea.

After the crash, several countries around the world have grounded the Boeing 737 MAX. Indonesia’s national airline, Garuda Indonesia, has taken the extra step of canceling its order of 49 additional 737 MAX jets due to low consumer confidence in the plane. Other airlines have not yet followed suit. Some have been keeping quiet on the topic, but WestJet has revealed its reasoning publicly: they are waiting for Boeing to create a solution and for regulators to approve it before making a decision. WestJet may have a long wait ahead of them: Canadian and European regulators are considering doing their own investigations into Boeing’s fix, instead of simply trusting the American Federal Aviation Authority (FAA). The FAA has been criticized alongside Boeing, for allowing aircraft manufacturers to essentially
self-certify their products’ safety. Both Boeing and the FAA have been dealt with several MAX-related lawsuits.

Boeing’s tentative fix involves updating the MCAS system to use both available AoA sensors, rather than just the one. They would alter the MCAS to prevent it from tipping the nose too far down. The AoA disagree light will also become standard, although the AoA indicator will remain an optional purchase. Pilot training for the 737 MAX will also be improved.

Investigation of the crash is still ongoing: whether or not Boeing’s fixes will be adequate remains unclear. It remains to be seen if thousands of the MAX will one day dominate our skies, or if the model will never fly again.

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