Hi Sonia,I think you have to have permission from the next of kin. Did your Grandad have a wife and is she still living. If you go to www.raf.mod.uk/community/support you will find a form to fill in to access his service records. I think there are two forms to fill in, one for if you have permission from next of kin and for if you dont. I sent for my Father's records last year and got them back in about a month. It costs £30. I don't know what their turnround time is now. Good luck.
Good news, your Grandma as his widow will not have to pay the £30. Ring: RAF Disclosure Section, Room 221b Trenchard Hall, RAF Cranwell, Sleaford, Lincs, NG34 8HB.Tel 01400-261201I found them to be very helpful.Best of luck.