The whole system was set up pre expeditionary RAF, it is geared to the 9-5ers who can do all the additional cr?p to get promoted.
The guys (and gals) who are away 6-8 months of the year on deployment do not get the chance to do the meals on wheels or scouts etc.
In my opinion the best way for NCA to get on the promotion ladder is to go down the instructional route as a lot of Sqn PICs are instructor posts.
The ground crew has the same problem, much more likely to get promoted on a MU than a Sqn
R1a