I knew someone who took an urn of ashes up in his his small airplane to be spread over an area the deceased requested. Everything went well until the pilot opened a side window and attempted to spread the ashes upon which the ashes blew back into the cockpit making a huge revolting mess inside.
It’s best to use a tube running out of a side window, and to aim it away from the leading edges. Ashes are very brasive and will strip your paint. Not to mention the indignity inflicted upon the deceased.