The report defines the economic implications to government and local agencies of modifications to airports, terminals, and enroute support facilities as a result of the introduction of a United States supersonic transport aircraft (SST) into scheduled commercial service by United States and foreign carriers. Costs associated with modifications to the ground environment and enroute support services which advanced, high-capacity commercial transport aircraft may require are identified. Only those improvement programs beyond the normal planning responses to increased traffic and technology advancements are attributed to the larger, faster airliners which will fly within the next 9 years. The costs of these aircraft-sponsored modification programs are allocated among the four competing aircraft: stretched subsonic (DC-8-63), high-capacity subsonics (B-747 and L-500), Concorde, and United States SST. (Author).