SASKATOON9999
Luton airport does not have its own rail station. EDIT Stansted and Gatwick on the other hand, being well designed and well run airports do have their own rail station
STN + LGW are built on broadly flat areas. LGW had a railway line there before it was built.
LTN is, if memory serves in the two weeks since I was last there, built on a hill and the railway line is in the valley.