Three months of public catastrophes led to what many believe was a necessary first step in addressing the Boeing Co.’s severe quality and safety issues. In a message to employees on Monday, much-scrutinized Boeing CEO Dave Calhoun announced he is stepping down from his role at the end of the year. Calhoun said his decision was influenced largely by the fallout of the technical fiasco of Alaska Airlines Flight 1282, where the door plug blew off the plane 16,000 feet above Oregon in January. “I have been considering for some time, in discussion with our board of directors, the right time for a C…