NY -- Standard&Poor's CreditWire 6/23/97 – Standard&Poor's today has assigned its single-'A'-minus rating to Philadelphia, Penn.'s $350 million airport revenue bonds series 1997A&B and 1998A issued for the Philadelphia Airport System. Standard&Poor's also has affirmed its single-'A'-minus rating on the city's $211.36 million outstanding airport revenue bonds, also issued for the airport system. The outlook is stable. The rating assignment reflects the following credit strengths: -- Strong local demand as evidenced by solid origination and destination travel patterns within the service area, and -- An affordable capital improvement program funded through a mix of bonded indebtedness, passenger facility charges, and grants-in-aid. These strengths are somewhat offset by concerns over carrier concentration, with US Airways