challenge it then! Why do you think perhaps that it’s not been challenged yet?
the most litigious country in the world (USA) still seem to have seniority within their major airlines. From where I sit in my armchair, my legal opinion is that it’s clear there isn’t a case to answer. Seniority is another word for loyalty in the legal world, and it’s been shown under U.K. case law that rewarding employees based on loyalty is in fact legal (or more accurately not illegal). See rolls Royce vs Unite the union for the case i refer.
You are (wrongly) making the assumption that seniority is age discrimination when it is crystal,clear it is not. There are pilots at BA that joined at 20 years old that are mega senior but still much younger than DEPs that joined post military service. How would you square that circle?
the merits and pitfalls of a system will be debated long after Corona is a distant memory, but I bet my pension there’s no legal challenge (who would even bring a case anyway?) in my lifetime.
remind me how the 65 mandatory retirement for pilots legal challenge went...