Seniority represents both direct and indirect discrimination and once tested in the Courts should become history
From October 2011 the 2006 Age Discrimination Act will be fully implemented and the 5 year period for companies and unions to become fully compliant will be over.
Pure seniority based selection procedures in all industries, not just aviation, will become a thing of the past, and not before time, for all the good reasons mentioned in a few of the previous posts.