So “long accepted” that it goes back well-before the origin of the English language. It reflects the societal insignificance of females historically, to the extent that when it became necessary to have a term for the other gender, it was always by something concatenated to the term for “man”. This reflected the fact that social power in those days was predominately a function of muscle mass. We are centuries removed from muscle being the determinant of power in society, but our language has not kept up.
This not about “hurt feelings”, any more than giving a freed slave “40 acres and a mule” made him an equal member of 19th century society. It has long been established that a society’s language both reflects and affects it. As long as its language describes more than half of its members using adjectival forms of “man”, there is the implication that they are a subgroup, not an equal party.
It’s high time that we eschew gender implications where none exists. We have perfectly good gender-free nouns for nearly every job in aviation. Our federal documents should reflect that.