I can accept that whichever way it goes will be a lot of changing in systems but isn't that a lot easier now using computers. This morning I was reading a post on another site regarding a Melbourne-Mildura flight. The poster used the codes MEL-MIA which to me (IATA based) would be Melbourne-Miami. Sure Mildura is YMIA for ICAO but YMEL is Melton Airfield, Vic. So the poster has just used the ICAO codes minus the "Y" and come up with a route that has confused both ICAO & IATA 'followers.' Now if both codes were the same, and codes for LONDON (City not Airport) were not required within the ICAO based system, then it wouldn't be needed to be put into ICAO system. Same as YMIA for Melton Airfield would not be needed for the IATA system. I don't see that it would confuse the whole idea if there were various codes that were not being used by one or the other. Specific Airline codes are gradually changing to 3 rather than 2 figures/letters AA to AAL, BA to BAW, for instance), so changes can be made when required. I still say that it would be beneficial to have only one code for each Airport. Maybe as ICAO is an "Governments official" organisation then it would make sense that the ICAO codes are the ones to stay and IATA should just have to agree to use the same codes. I don't suppose it will ever happen as even car manufacturers can't agree on which side of the steering column the windscreen wiper control should be on, but it would be nice if people/organisations/manufacturers could get together and sort things out.