Psr777
Using seniority in selection for promotion is probably indirect discrimination against women under the sex discrimination legislation brought in 30 years ago. As far as I am aware, no one has brought a case challenging this.
Although we do not yet have any case law to prove one way or the other, my own view is that selection for promotion based on length of service (ie those with the longest service automatically get the first opportunity to be promoted) is probably direct age discrimination under UK law.
It would be a brave pilot who challenged this in the courts. However, case law from other industries might take the matter out of airlines' hands.
RHRP