Singapore  carriage of transponders The Singapore Maritime and Port Authority (MPA) issued a circular stating that, with effect from 1 January 2012, all power-driven vessels regardless of size will be required to be fitted with a working transponder as a port entry requirement. The transponder may be one of the following types: (1) IMO AIS Class A; (2) IMO AIS Class B; or (3) MPA HARTS. Port Marine Circular 10/2010 (6/7/10). Note: For some unknown reason, the circular fell off the MPA website. Therefore, I have posted a Copy on my site. Since the MPA site does not explain the unposting, we do not know if it was accidental or if the original posting was in error.