Still knocking a few ideas about at the moment. Did look at the Transponder Landing System. Seems like a cracking piece of kit but expensive. The military are all going across to JPALS in several years' time, which is a GPS based system, but looking for something sooner. Have a dog legged approach to the non-instrument runway here due to LHR, so ILS is unsuitable. Most inbounds are gucci biz-jets so most of them are GPS equipped. Don't worry, there'll be plenty of work going into planning of procedures, acqusition and sustainment etc.