New York City Mayor Eric Adams is under FBI investigation for free flight upgrades, RadarOnline.com has learned. Adams reportedly received free upgrades from Turkish Airlines that bumped him up to first class status. According to the New York Times, federal investigators are looking into Adams’ mayoral campaign — and have zeroed in on free airfare upgrades. The embattled politician received complimentary upgrades on the highest seat class available for commercial passengers on international flights. The probe is part of a broader corruption inquiry involving Adams, aides to the mayor and a top…