i believe the PC9s and Alpha jets are mainly operated out of Boscombe down which s the RAFs research base if you like,they were evaluate and test upgrade configurations.One of the PC9s is an ex Saudi aircraft which was included as part of a research contract to test certain parts or specs of a potential upgrade of the Sauid Tornado fleet.im not sure about the other PC9?the alphas were bought by the RAF to evaluate them against the British hawk in which the hawk emerged as the winner of that evaluation.they have all sorts of aircraft at boscombe, including a venerable Havard trainer from WW2 which is still carrying out that role to this day which is quite an achievement!