Helicopter Sikorsky S-55C Serial 55-1206 Register 51206 used by Royal Thai Army. Built 1958. Aircraft history and location Aircraft History 51206 Royal Thai Army 1958-07-18Sikorsky S-55C, c/n 55-1206, ff? reg Sikorsky as N9F, 1958 accepted RTA as 51206, 18Jul58 left factory gates 23Jul58. Send Updates Use APP to upload photo @ (optional) When Now? / / Send