I suggest that if too many fail any course then there is something wrong with selection, course, examination, system - conversely if all pass then there is likely to be something wrong as well - If the training/examination system works correctly then a pass rate of 70-90% should be acceptable and indicates a correct balance between all the elements.
Examinations are as much about checking that the selection/training system is working as checking that the student is competent. It is of course more efficient and fair for all concerned if those that cannot attain competence are removed from training before the final examination stage - so my 70-90% is a course pass rate, not a final examination pass rate.
Cheers