CDAs
CDAs are in place at Heathrow, Gatwick and Stansted, they have been for years. The BAA, NATS, DfT, Airlines and the CAA all co-wrote the Arrivals Code of Practice in 2002. Since then CDAs have become the primary noise reduction measure for arriving aircraft. Since the code was originally written it has been 'adopted' by other UK airfields, Europe and beyond. Eurocontrol have started a group looking at harmonising CDAs across Europe and using the Code of Practice as the guideline document. As Flightman points out, version 2 is at the printers and will hit the streets imminently.
Other work involving CDAs are at Manchester (at night at the moment), Luton on both 08 and 26, as part of their recent airspace extension, NEMA (P-RNAV) but also radar vectored approaches. Also as part of Sustainable Aviation, Commitment 15 is looking at a CDA outreach programme across the UK by the end of 2006. This programme is in progress, and will have updates by the end of the year.
In it's most basic form, a CDA is keeping an aircraft as high as possible for as long as possible. It's not rocket science!
In summary, CDAs are here to stay and they will affect controllers and operators. Doing nothing is no longer an option!
PS. Accountants love CDAs, as they save fuel, emission &, engine wear.