I'm not in the habit of scaling exams, although I'm aware that the practice is widespread and highly recommended in some circles (such as grading on a curve). To my recollection, none of my college instructors scaled exams or wrote any policy about such on their syllabi. I'm wondering if one did commit to an official policy of scaling exams, what would a reasonable written policy look like?
The goal here would (hypothetically) be similar to Krantz in How to Teach Mathematics (Sec. 2.10): "My main goal in formulating my grading policies is to make the greatest number of students feel that they have been treated fairly (and, not incidentally, to reduce student complaints)." Secondarily (and again hypothetically), to defend against possible future administrative complaints that the instructor is not matching some recommended grade proportions (same section by Krantz).
Please assume that the individual exams are adequately fair assessments themselves (not broken, vague, or overly-hard questions, cover same topics covered in class and homeworks, sufficient time permitted, significant advance time taken assessing questions and grading rubric, etc.).
Background: I'm at an open-admissions community college where high failure rates are historically common, often half or more of many math or computing courses. Among the things I'm worried about if I started doing that are: Would there be any lower bound to what might wind up being passing work?
For example, I had a colleague at a different university (top-20 in U.S.) who got in trouble a number of years ago in that, when pressed by students on his scaling policy, said that if every single student got a zero on a exam, then the scaling process would turn all of them into 100% marks. Surprisingly, the students successfully organized a total boycott of the final exam, and my friend followed through and gave 100% marks to everyone as per his word. (This turned out to be quite embarrassing for him.)
So I'm wondering what kind of formal, mechanical policy for scaling would prevent no-lower-bound situations similar to this one?