Boeing and Airbus are mortal rivals. Boeing designed the 737 back in the 60s, and made the landing
gear short as most airports back then lacked infrastructure needed to
load passengers and cargo into aircraft that sat higher off the ground. Thus they designed the 737 to sit low to the ground. Then came the 737 classic, with bigger and more efficient engines, (Larger engines = higher bypass ratio = more fuel-efficient), still
small enough to fit under the wings, negating the need to make the landing
gear taller and a whole lot of recertification. Then came the Airbus A320, which sold like hot
cakes. Boeing needed a competitor, so along came the 737NG, same
story as the 737 classic. And then came the A320neo, with higher bypass engines, and once again Boeing needed a competitor so the 737
MAX was born. Principally, to fit the Boeing 737 MAX’s larger engines under the wings while keeping the airframe low to the ground, Boeing moved them forward and upwards. The
low-slung design also suited
low cost carriers which don’t use airport infrastructure (lifts, stairs, jetbridges, etc) to save costs.
The larger engine nacelles can create significant lift at higher angles of attack due to their placement relative to the centre of lift produced by the wings, which can cause the
nose to pitch up during flight in certain situations, increasing the likelihood of an unintended and unrecoverable stall which would change the flight characteristics of the aircraft and require recertification and retraining. To avoid this, Boeing created to the MCAS (Manoeuvring Characteristics Augmentation
System) software to detect this pitch-up and push the
nose back down, so the MAX behaved and flew exactly like a 737NG,
classic and all earlier iterations. But Boeing, in their
silly rush to compete with the A320neo, coded MCAS to read off
one angle of attack (AoA) sensor, and didn’t tell anyone about it’s existence, so pilots knew nothing about it because if they did, they’d need retraining and the MCAS would require certification.
Early reports from Indonesia's Lion
Air investigation suggest that a faulty sensor reading triggered the MCAS suddenly after takeoff. It's known that a similar event may had occurred in the recent Ethiopian Airlines
crash. Basically the pilots had no knowledge of the software and how to override it since they simply weren’t told about it. The Boeing 737 MAX is very
safe now, thankfully.
