Well I think all so-called final salary pensions are fractional at best i.e. have long been restricted by pensions law to something like 40/60ths (2/3) max of final salary. I think some or all NATS members are on 56ths but not more than 37/56ths max I would imagine.
The point is that NATS scheme is currently one of the best in the country and long may it remain so courtesy of strong lobbying for the "right thing" through thick and thin by right thinking members and citizens,
anotherthing 
The day it gets sold down the river (frozen or closed to new entrants or wound up in favour of a cheaper scheme) by the trustees/directors and/or ERG at CAA will be a sad day indeed. I'd rather see ATC charges doubled before that day, but I'd worry about where the extra money might actually end up ... and that is sadder still, I suppose.