The trouble is, the group any FRI would be aimed at are already pensionable under legacy schemes; leaving means a pension uplift that the FRI would have to counter for every year retained before you even start a retention intitiative - £50k isn't even close.
I personally like the idea touted by a brilliant mind in Manning a few years ago - if it costs £X millon to train a pilot, then pay 1/2 £X million to retain an experienced one for, say, 10 years.
Apparently it wouldn't pass The Sun Test...but everyone leaving does???