The phrase "impartial manner" means being fair and unbiased, treating everyone or all sides equally without any personal preferences or favoritism. Full definition
Mentoring sessions conducted in a fair and impartial manner with restraint from promoting individual breeding programs and / or promotion of individual dogs or bias toward other breeding programs. (italiangreyhound.org)
Julie Allison, an attorney for the home, said in a statement Friday, «We will be addressing these matters in court, and we look forward to sharing all of the evidence that has been obtained and that will be considered in a fair and impartial manner by the judge.» (nbcmiami.com)
You can, of course, write on a piece of paper that this «truth commission» will be fair and non-partisan and always examine the best evidence in a totally impartial manner. (politics.stackexchange.com)