I left in 1977 well before the second pension was introduced . I paid GPNI during my service and, as far as I am aware, the rate we paid was exactly the same percentage of our pay as that paid by civilians. There was one difference - our pay was much less than what a civilian aircraft engineer earned - presumably because we received 'free' food and lodgings.
For those who served from 1978 when SERPS began, there being no pension for a 12 year or less engagement, there is no "occupational pension" entitlement so how could anyone on such an engagement be considered "contracted out"?