Ever since Delta and US Airways agreed to swap slots in August, observers have been reading the tea leaves for merger implications. US Airways traded slots at New York's LaGuardia Airport for slots at Washington Reagan National and Narita. It also traded a Rio route authority for an unrestricted Brazil route authority. The deal requires regulatory approval. Delta already has multiple Brazil authorities, and is not impacted by having one limited to Rio. US Airways, however, could fly from Charlotte to either Rio or Sao Paulo, or could alternate service. Already, the deal has led US Airways to say it will give up its Philadelphia-Beijing authority, preferring to focus on Phoenix-Tokyo as its Asian gateway. US Airways is weakened in the New York area, but Parker noted that even today it has just 4% of the traffic. (Delta dominates LaGuardia, with American second.) But US Airways becomes stronger at National, with more than 50% of traffic. Theoretically, it could become tougher for US Airways to get regulatory approval to merge with United, which has a hub at Washington Dulles. -- Written by Ted Reed in Charlotte, N.C. .