The Air Force is operating the MCAS-equipped KC-46 without incident or concern; there is nothing intrinsically wrong with the software. But porting it to the civilian 737 MAX led to disaster.

The Boeing KC-46 Pegasus is a U.S. Air Force aerial refueling and strategic military transport aircraft, which debuted with the service in 2019. The winner of the KC-X tanker competition to replace the aged Boeing KC-135 Stratotankers, the new KC-46 is expected to be a bulwark of the tanker fleet for decades, with the Air Force expected to procure nearly 200 of the new aircraft before 2027—assuming certain structural problems can be addressed. Notably, the KC-46 is the aircraft for which Boeing’s now notorious MCAS software was developed.

How Boeing Won the KC-X RFP

In 2006, the Air Force issued a request for proposal (RFP) for the KC-X program. Two aircraft proposals were ultimately considered, both developed from commercial airlines. The first, proposed in conjunction between Northrop Grumman and European commercial jet manufacturer Airbus, was the KC-45, a variant of the Airbus A330 commercial airliner. The second, proposed by Boeing, was the KC-46, which took a similar tack in developing an aerial refueler from the Boeing 767 commercial airliner. The two proposals pitted the two dominant corporations in commercial aviation against one another for a military contract, in a posture that mirrored the competition that was ongoing in the commercial sector; Airbus had risen from humble origins to encroach further and further upon Boeing’s market share, which had once seemed impenetrable. Now, with the KC-X contract at stake, Airbus threatened to encroach upon the military market, too. But Boeing ultimately won, and began developing the KC-46 Pegasus from the 767.

Introducing the KC-46 Pegasus

In 2018 and 2019, two Boeing 737 MAX 8 crashes would later be linked to a new software, the MCAS (Maneuvering Characteristics Augmentation System). During the investigations and hearings that would follow, the MCAS came to be closely associated with the 737 MAX. But the MCAS was actually designed for a different aircraft: the KC-46 Pegasus.

The MCAS software, in theory, senses when an aircraft is pitching upwards in a manner that risks a stall. When such an attitude is detected the MCAS kicks in to automatically deflect the horizontal stabilizer of the aircraft upwards and push the nose of the aircraft downwards in order to prevent a stall. The technology was developed for the KC-46 to mitigate the manner in which the tanker’s center of gravity shifted when rapidly offloading fuel.

When Boeing was developing the 737 MAX, the company noticed that the modified 737, with larger engines placed forward of the wings, had a tendency to pitch upwards. To correct the tendency, Boeing borrowed the MCAS software that was being developed down the line with the KC-46. However, the software could not simply be ported from the KC-46 to the 737 MAX for two reasons. First, the KC-46’s MCAS uses two angle-of-attack sensors to inform the MCAS, ensuring redundancy; the 737 MAX lacked this feature. Second, the KC-46’s MCAS automatically disengages once the pilot makes an adjustment on the stick.

The two differences made a profound difference in the safety of the aircraft. The Air Force is operating the MCAS-equipped KC-46 without incident or concern; there is nothing intrinsically wrong with the software. But when ported to the 737 MAX, the MCAS caused two plane crashes—grounding the entire fleet and forever marring Boeing’s reputation.

About the Author: Harrison Kass

Harrison Kass is a senior defense and national security writer with over 1,000 total pieces on issues involving global affairs. An attorney, pilot, guitarist, and minor pro hockey player, Harrison joined the US Air Force as a Pilot Trainee but was medically discharged. Harrison holds a BA from Lake Forest College, a JD from the University of Oregon, and an MA from New York University. Harrison listens to Dokken.

Image: Shutterstock / Ian Dewar Photography.

The post There Was Nothing Wrong with Boeing’s “MCAS” Software—Except the Plane It Was On appeared first on The National Interest.