cut-n-paste from a NBAA update email:
"NBAA recently became aware that a U.S. Part 91 flightcrew was grounded in Europe following a safety assessment of a foreign aircraft (SAFA) check, despite the fact that both pilots held valid second-class medical certificates. While possession of a valid second-class medical certificate is sufficient to exercise the privileges of a commercial pilot certificate in the U.S., the requirement is inconsistent with ICAO standards and recommended practices. NBAA urges pilots exercising commercial and airline transport pilot privileges flying internationally to possess a current first-class medical certificate."
"NBAA recently became aware that a U.S. Part 91 flightcrew was grounded in Europe following a safety assessment of a foreign aircraft (SAFA) check, despite the fact that both pilots held valid second-class medical certificates. While possession of a valid second-class medical certificate is sufficient to exercise the privileges of a commercial pilot certificate in the U.S., the requirement is inconsistent with ICAO standards and recommended practices. NBAA urges pilots exercising commercial and airline transport pilot privileges flying internationally to possess a current first-class medical certificate."