More than a year after an unsolicited proposal was first submitted, the Subic Bay Metropolitan Authority (SBMA) has formally launched the Swiss challenge for the ₱6.2-billion Subic Bay International Airport (SBIA) project, opening the door to rival bidders for an airport that would complement the seaport facilities in the former United States (US) naval base in Zambales province.In an invitation posted on the website of the Public-Private Partne…