Boeing 737 MAX came without safeguards used in military jet

The MCAS system on the 737 MAX, which Boeing has redesigned after two fatal MAX crashes that killed 346 people, is similar to a system Boeing had previously developed for the KC-46 military refueling tanker.

The military version was designed to receive information from multiple sensors and was limited in forcing the nose of the plane down to prevent the pilot from losing control of the plane.

But when Boeing built its new 737 Max passenger plane, it did not include the same safeguards.

A Boeing software fix for the MAX will mean its flight control system will now function more like the military version of MCAS. It will now use data from two, rather than only one, angle of attack sensors, which is intended to make the plane less vulnerable to a single malfunctioning sensor. It will also make the system push the plane downward less frequently and with less force.

Boeing said in a statement that the MCAS for the two planes were designed differently because of different sizes, weight distributions, and missions.

"The KC-46 tanker does use a Maneuvering Characteristics Augmentation System (MCAS) flight control law. However, the architecture, implementation, and pilot interface of the KC-46 tanker MCAS are different than that of the 737 MAX. The systems are not directly comparable," the company said in a statement.

The Boeing tanker is a version of the 767 jet modified to carry fewer passengers but a large amount of cargo and 210,000 pounds of fuel, according to a company fact sheet.

The Federal Aviation Administration, which certifies US civilian aircraft, did not immediately comment when reached Monday morning on why it required a different standard than required by military reviewers.

Over the weekend, the Wall Street Journal reported details of differences between the military and MAX versions of the MCAS system.

Preliminary reports into the two crashes, of Lion Air and Ethiopian Airlines flights, describe the automated system repeatedly pushing the plane's nose downward, plunging them into fatal and unrecoverable dives. Further reviews of the crashes, FAA procedures, and Boeing's actions are ongoing.

Boeing's past public statements suggest it will soon submit the software fix and other changes to the Federal Aviation Administration, which certifies civilian aircraft in the US, and its counterparts worldwide. In the meantime, the MAX remains grounded worldwide, the longest grounding of a major aircraft.