(CNN) Boeing built its 737 MAX passenger jet without safeguards the US military required for a similar flight control system on a different Boeing-made plane, a source with knowledge of the MAX system told CNN.

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.

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.

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